The endocrine basis of breeding behaviour in the feral pigeon (Columba livia): I. Effects of exogenous hormones on the pre-incubation behaviour of intact males

Anim . Behav., 1969,17, 286-306

THE ENDOCRINE BASIS OF BREEDING BEHAVIOUR IN THE FERAL PIGEON (COL UMBA LI VIA) : I. EFFECTS OF EXOGENOUS HORMONES ON THE PRE-INCUBATION BEHAVIOUR OF INTACT MALES BY R. K . MURTON, R . J. P. THEARLE & B. LOFTS

Ministry of Agriculture, Fisheries and Food, Infestation Control Laboratory, Worplesdon, Surrey, and Department of Zoology, University of Hong Kong

It has long been known that androgens will restore male-type sexual activity to castrates (Beach 1948 ; Collias 1950), increase social status and aggressiveness (Bennett 1940) and even induce male-like behaviour in females (Leonard 1939 ; Shoemaker 1939). Conversely oestrogens are well known to 'feminize' male birds and to eliminate male attributes (Bennett 1940 ; Davis & Domm 1941), though it is also true that there are many exceptions to these generalizations . There are also circumstances when direct hormone responses do not seem to be involved ; for example, either sex may exhibit a duality of behaviour which can loosely be termed male or female in type, and this led Morris (1954, 1955) to refer to 'pseudo-female behaviour' when males engage in soliciting and other female-like actions . This kind of sexual inversion seems to occur in conflict situations (Hinde 1966) . Castration of pigeons markedly reduces sexual behaviour but copulation (Carpenter 1933a) and courtship feeding (Carpenter 1933b) are not completely eliminated and there are many other, apparently conflicting, observations of this kind . Such results have been considered to support the view that hormones function only in predisposing a particular excitatory state, within which inherent neural mechanisms operate . While this may well be true, in experiments involving castration the possibility that pituitary gonadotropins might directly have facilitated certain displays seems to have been overlooked. That both oestrogen and androgen secretions potentially exist in either sex has also long been appreciated ; for instance, the avian testis is known to produce oestrogen which, acting synergistically with prolactin, is necessary for brood patch development in hypophysectomised male birds (Bailey 1952) . In spite of such observations it has been usual to consider oestrogen production by males as an accidental consequence of the common evolutionary history of the sexes without ascribing to it a positive ethological or endocrine function, Indeed, in a review Van

Tienhoven (1961) stated `whether or not oestrogen plays a role in the regulation of some of the reproductive functions of males cannot be stated definitely until evidence of oestrogen secretion during various parts of the reproductive cycle has been obtained' . We believe that we now have such behavioural and endocrine evidence enabling us to suggest important functions for oestrogen in the normal reproductive cycle of male pigeons, and this is partly shown here . With regard to the hormone basis of much avian behaviour the studies of Lehrman and his associates (see Lehrman 1961 for summary) and Hinde and his co-authors (see Hinde 1967 for summary) are exceptional in developing and extending the pioneer investigations of workers like Beach (1948) and Collias (1950) and in giving quantitative results . In particular, they have emphasized how specific external stimuli may cause specific hormone secretions . Lehrman has not, however, been concerned to examine the reproductive organs of his subjects in order to correlate hormonal and behavioural states with gonad histology . Similarly endocrinologists, who have for many years appreciated the gross effects of exogenous hormones on the gonad-pituitary axis have not been concerned to define the behaviour of their animals . In short, there is now a need to correlate the endocrine basis of the avian reproductive cycle with behavioural manifestation and to link both with gonad and pituitary cytology . This then has been our aim in the present studies and we have begun by trying to define the effects of exogenous hormone treatment on normal intact male pigeons . For this purpose we have been able to build on the studies of Fabricius & Jansson (1963) . The present paper deals with the effects of the three gonadal steroids (androgen, oestrogen and progesterone) and three pituitary hormones (follicle stimulating hormone, luteinizing hormone and prolactin) on the normal pre-incubation behaviour of the pigeon, Gonad histology 286



MURTON et al. : THE ENDOCRINE BASIS OF BREEDING BEHAVIOUR IN PIGEONS

and endocrine implications will be dealt with fully in subsequent papers, but certain findings are mentioned and discussed when necessary for a proper appraisal of the present results . Methods Procedure Subjects were selected from mixed stocks of adult feral pigeons Columba livia held in large outdoor aviaries with a breeding house attached . Their previous breeding history was unknown and many were presumably experienced . Birds were chosen with uniform plumage and physical characteristics, those most nearly resembling wild-type or of the blue-chequer variety being preferred. An initial attempt was made to obtain an equal sex ratio, sexing by physical characters being possible to a moderate extent . Subjects were then kept singly in cages arranged in pairs with an opaque removable partition . The cages were in an indoor room kept at about 18° to 20°C and with a daily 17-hr photoperiod. Cages were so arranged that the birds could not see each other, although they could hear nearby,birds. After one week all the birds were laparotomized ; an incision was made between the eighth and ninth ribs under Nembutal and open ether anaesthesia, and the gonads were examined and measured in situ . Only males with testes larger than 19 . 0 x 6 . 0 mm were retained . Females with largest follicles greater than 5 . 5 mm in diameter or smaller than 0 . 5 mm were discarded (see Table II) . The remaining birds were considered to be as uniformly in reproductive condition as was practicable and were allocated to pairs of cages measuring 102 cm wide x 46 cm deep x 41 cm high, though each bird was still kept separate .

2 87

After a recovery period of three days the partition was removed on a Monday and the birds left together until the male gave the bowing display. If this was not achieved within 15 min the birds were tested again later in the day and if necessary kept separate for a further week when another attempt was made . Occasionally an apparently normal male did not perform even after several attempts and it was then discarded. Satisfactory subjects were kept separate through the remainder of the week (Tuesday-Sunday) during which time experimental treatments were begun . The experimental schedule is shown in Table I . Throughout the period of pairing, nest material, in the form of small twigs and pine needles, was available in both the male's and female's cage and in addition a nest-bowl was left in the female's compartment . As many experiments were conducted spanning a long period it was not practical to commit every weekend to injection and observation, but it will be seen that the procedure has not detracted from the results, although it did cause some setback to the cycle on the Monday, when observations were resumed, and this is reflected in some of the figures (e .g . Fig. 1). Behavioural analysis . During the daily 30-min periods of observation three pairs were watched simultaneously in cages arranged one above the other . As any particular display occurred it was allocated to an appropriate 2-min sub-period . Thus if preening occurred at some stage during the 2 min it was scored as a positive record irrespective of how many times it occurred . In some instances it was possible to record the total frequency of a display and full display

Table I. Experimental Schedule Second and third weeks

First week Monday

Initial test pairing

Thursday

a .m . All birds killed

Males given daily hormone injections ; birds kept separate

a .m. Males given daily hormone injections p .m. Birds paired (d' x Y) for 30-min observation period

No injections ; birds kept separate

No injections ; birds left paired

Tuesday Wednesday

I

Friday Saturday Sunday

Fourth week

288

ANIMAL BEHAVIOUR, 17,

sequences, depending on how much activity was taking place . The results are mostly considered as the number of 2-min periods (15 being the maximum for one day) for which a particular display was recorded . For all experiments there were six pairs of birds, except one experiment involving LH injections where only five pairs were studied. Thus for each day there was generally a total of 90 observation periods each of 2 min and 900 (6 x 150) for the whole experiment . This observation technique is the one used by Fabricius & Jansson (1963) based on original work by Carpenter (1933a) and Beach (1951) and it can be considered to be well tested . The tables and histograms give the mean score for each display for groups of birds receiving any particular hormone treatment . These data are not appropriately treated by t-test assumptions and the 1-tailed probabilities quoted have been obtained using the Mann-Whitney U test . In some cases there was a wide variation in the scores following hormone treatment, whereas untreated controls were reasonably uniform in their responses . This method of recording tends to underestimate the differences between treatments because a display which was reduced in frequency using the 2-min score system usually also occurred much less frequently within each period . Thus the total number of instances, could this have been recorded, would have shown more marked differences between many of the treatments . For those data which were specially collected to define chains of behaviour, as in Table VII, a chi-square test has been used . The totals column in Table VII is also an indication of the frequency of the displays, these observations being made as often as possible without reference to any particular 2-min period. These figures are thus additional to the data depicted in the other tables and histograms. Hormonal treatment. The males of each group (six pairs in all but one of the groups) received 14 hormone injections made alternately into the left or right pectoral muscle, the amounts per injection being : Group 1 . 0 . 5 ml saline only (controls) . Group 2 . 2 mg testosterone proprionate in 0 .4 ml arachis oil . Group 3 . 2 mg oestradiol benzoate in 0 . 4 ml arachis oil . Group 4 . 2 mg progesterone in 0 . 2 ml arachis oil with 10 per cent benzyl alcohol,

2

Group 5 . 1 mg NIH-LH in 0 . 5 ml saline (5 males only) . Group 6 . 1 mg NIH-FSH in 0 . 5 ml saline . Group 7 . 2 mg Armour prolactin in 0 . 4 ml saline. A fairly long pre-treatment with the various hormones was given to ensure plenty of opportunity for their effects to be manifested when behaviour observations were started, though other work by Vowles & Harwood (1966) on the effects of hormones on aggressive behaviour in Streptopelia risoria suggests that this may have been unnecessary . Results 1. The Normal Pre-incubation Behaviour of the Controls A brief description of the behaviour patterns measured is given below : BOWING . While walking the bird bows towards the ground, utters the 'bow-call' and rises onto its toes, at the same time stretching its neck, spreading and raising its tail. During bowing the bird frequently rotates ('pirouetting') . ATTACKING INTENTION . Standing in a normal position, the bird pecks towards its opponent without actually attacking . ATTACKING. The bird grasps its opponent's feathers (usually in neck or head region) and sometimes beats it with its wing . Alternatively, the wing may be flicked at the opponent with or without delivering a blow and the pecking movements may be absent . DRIVING . The male chases the female very closely, almost treading on her tail . STRUTTING . With neck raised one bird (usually the male) walks round the other . BEGGING. One bird (usually the female) pecks gently at the base of the other's bill . COURTSHIP FEEDING. In response to begging by the female, the male opens his bill and allows the female to insert her bill and be fed (the action resembling the movements involving in feeding of nestlings) . Sometimes a female will feed the male and following certain hormone treatments the male will offer to feed the female in the absence of preliminary begging . SOLICITING . The female squats, spreads her wings and tail, and `invites' the male to mount . MOUNTING. The male jumps onto the back of the female, making treading movements and spreading his wings. COPULATION . Self-explanatory. NEST DEMONSTRATION . The bird squats, repeatedly nods its head towards the floor,



MURTON et al. : THE ENDOCRINE BASIS OF BREEDING BEHAVIOUR IN PIGEONS vibrates the wing nearest to its partner and utters the 'nest-call' . At low intensity the display may involve wing vibration only, without the bird crouching . NIBBLING . One bird gently manipulates the feathers of the other (usually in the head region), normally during nest demonstration . PUSHING. While one bird is nest demonstrating, the other makes efforts to push it off the nest site . Sometimes the pushing bird rushes the full length of cage at the individual giving the nest demonstration . MOULDING . Whilst on the nest, the bird rotates its body and scratches with its feet . PECKING . The bird pecks at the floor or other objects without actually taking anything into its beak. PECKING AT TWIGS . As for pecking, but directed only at twigs or other nest material . TWIG CARRYING. The bird picks up a twig and carries it in the direction of the nest . (If a bird picks up a twig, adjusts it into a carrying position and then drops it, this has been referred to as twig manipulation.) NEST BUILDING . One bird carries a twig to the other on the nest and either drops it in front of the sitting bird or places it in the nest . The sitting bird will then pick up the dropped twig and place it in the nest, or arrange the twig already in the nest . Sometimes one bird will nestbuild without the co-operation of its partner . DISPLACEMENT PREENING . The bird rapidly touches the scapulars with its bill, which is then withdrawn quickly. PREENING . The bird engages in proper feather maintenance . FOOD PECKING. The bird pecks at or picks up food, but does not attempt to eat it (false feeding) . FEEDING. Self-explanatory . STANDING . Self-explanatory. Fabricius & Jansson (1963) should be consulted for a full description of the normal preincubation behaviour cycle and also for a full definition of the terms used to describe the various displays . Unlike the above authors, the term courtship-feeding is employed here instead of billing, it being a truer description of what happens . Pigeons often fondle each others' bills when engaged in nibbling without true courtshipfeeding occurring and this could more appropriately be termed billing . There are two dominating sequences of behaviour ; the first leading to copulation through

289

displacement preening and courtship feeding ; the second leading to nibbling and twig carrying via nest demonstration . Although each activity may be followed or preceded by several others, these two chains of behaviour predominate . Fabricius & Jansson also state that the actions which compose the courtship pattern seem to form three fairly distinct groups : the first of these consists of primarily aggressive behaviour represented by bowing, attacking intention and attacking (driving is associated with this group more closely than with any other) ; the second group is sexual behaviour proper, consisting of displacement preening, begging, courtship feeding, soliciting, mounting and copulation ; and the third group is formed by nest demonstration, pushing, twig carrying and nest building . The present observations on the six control pairs mostly support these conclusions and although at times a mixture of different types of activity did occur, the gradual transition from one behaviour group to the next was clearly apparent . Fabricius & Jansson state that the first response shown by the female to bowing is almost invariably pecking, that pushing was only observed in females, that begging only occurred in females, and that copulation does not occur until about the 4th or 5th day of the cycle . In the present study pecking was never recorded for the female as a response to bowing ; pushing was observed in all six males ; begging was observed in three males ; and copulation occurred in three pairs on the 1st day and in two pairs on the 2nd day . Driving was recorded much less frequently than by Fabricius & Jansson . According to these authors, females carry twigs earlier than the males, but in the present study only one of the control females was first to initiate the behaviour . Both twig carrying and nest building become common in the male only when the female is well established in nest demonstration on the nest site, and the male than spends long periods collecting twigs and carrying them to the female for nest building . Our observations were somewhat obscured because twig carrying in controls seemed to reach a peak on days 6 and 7 after pairing when the birds were together over the weekend and no observations were made. The appearance of twigs in the bowl on day 8 showed that nest building had taken place . Even so, in the pairs which showed this behaviour before the 6th day, it was always the male which did so first . The general sequence of events seen throughout the cycle was also apparent, to a lesser



290

ANIMAL BEHAVIOUR, 17, 2

extent, in the 30-min observation periods ; bowing and aggressive behaviour occurred as soon as the birds were paired, leading onto courtshipfeeding displays and finally to nest demonstration . At the beginning of the cycle aggression and courtship-feeding dominated, but gradually gave way to more nest demonstration until, towards the end of the cycle, a brief bowing display would lead almost at once to nest activities . 2 . Pre-incubation Behaviour of Hormone-Treated Birds In the control birds there was a fairly clear-cut pattern of events with one group of behaviour sequences leading on to another throughout the cycle (bowing-courtship-feeding-nest demonstration-nest building) . When the male of a pair had been treated with a hormone this pattern became less well defined ; this was true for all six of the hormones under investigation, although perhaps rather less so for androgen and luteinizing hormone . With each of the six hormones we formed a general impression of the change in behaviour, regardless of points of detail . With LH, the birds behaved much as did the control birds but were less active ; although most of the behaviour sequences occurred, they were weaker and less pronounced than in the control birds . With FSH

the most outstanding feature was the general increase in aggressive activity on the part of the male ; this was also true for androgen but the aggressive behaviour tended to lessen after the first few days, and this was not always the case with FSH . With oestrogen there was a great emphasis on nest demonstration and associated behaviour, particularly in the males ; this emphasis was so great as to affect the whole behaviour cycle . With both prolactin and progesterone there were wider variations in behaviour among the six pairs, but the general impression was one of severe reduction of all sexual behaviour sequences, with the birds behaving like well-established pairs. Table II shows the number of pairs in each group that produced eggs and the time that the eggs were laid, and reflects the effect of the hormone treatments ; both prolactin and progesterone treated groups differ significantly from the control group in the number of eggs laid and the time of laying (P<0 . 05, 1-tailed), while the difference between the control group and FSH or oestrogen groups is not significant (time of laying ; FSH P = 0 . 09, oestrogen P = 0 .09, 1-tailed). All eggs were laid from the 8th day (from pairing) onwards and no observations were made on days 13 and 14 (observations

Table H. Reproductive Conditions of Females Used in Hormone Experiments Mean diam. of largest follicle (mm) Hormone treatment Start

End (birds that did not lay)

Control

4 .2 (2.0-5 . 0)

LH

Egg laying

Mean oviduct weight (g) (birds that did not lay)

No . of birds that laid

No . of eggs laid

Day (after pairing) of first egg

7 .75 (4 . 0-11 . 5)

4

8

9

4.1 (2.0-5 .5)

13 .5 (12 . 5-14 . 5)

3

5

8

7 . 35 (6 .58-8 . 12)

FSH

3 .25 (2 .0-4. 5)

12.9 (7 .0-16. 5)

2

3

12

7 .98 (4 . 17-11 .22)

Prolactin

2 .75 (2 .0-5 .0)

12 .7 (9 .5-17.0)

1

1

13-15

7 .23 (3 .71-9 . 58)

Androgen

4.0 (2 . 5-5 .5)

9 .75 (4 . 0-15 . 5)

4

6

12

7 .91 (6 . 44-9 . 38)

Oestrogen

2 .3 (0 . 5-3 .5)

10. 5 (7 . 0-14 . 5)

2

3

13-15

5 .26 (1 . 58-8 . 47)

Progesterone

3.0 (0 .5--4 .5)

8.9 (5 .0-15 .0)

1

1

13-15

2 . 93 (0 . 93-7 . 20)

Ranges liven in parentl

6 . 66 (6 . 48-6 . 83)



MURTON et al. : THE ENDOCRINE BASIS OF BREEDING BEHAVIOUR IN PIGEONS

being completed on day 12) though a record was taken on the 15th day, before the birds were killed . Observations made after eggs were laid have not been included in the histograms and tables . The diameter of the largest follicle and the oviduct weight at the end of the experiments (Table II) for those birds which did not produce eggs gives an indication of the degree of reproductive development. The numbers of birds which did not lay are too small to give significant differences between treated groups and controls, but if one considers the females from the prolactin and progesterone groups (where only one bird laid in each group) it can be seen that the progesterone birds were not so close to laying as the prolactin birds (largest follicles P<0 .05 ; oviducts P < 0 .05 1-tailed) . The effects of hormone treatment on particular acivities are described below . A. Bowing, Attacking and Driving Luteinizing Hormone . The total incidence of bowing (Figs 1 and 2) and attacking (Fig . 3) by males was very slightly lower than in the controls (not statistically significant) but this caused a tendency for the females to show less inclination to retreat and instead to respond by themselves bowing (Fig . 2) . Soliciting did not

N ~ O .~ N~~ O 00 00

N rn 00

L .H.

FSH

PROL .

29 1

0

O O 00

AND.

OEST.

R

0

to 00

PROD.

Fig. 2 . Mean incidence of bowing display by paired males (solid columns) and females (hatched columns) depending on hormone treatment of the males. Birds were paired for 30 min per day over 10 days and the scores refer to the mean number of 2-min sub-periods per bird during which the behaviour was recorded . Probabilities (Mann-Whitney U test) are detailed . See `Methods' for further details .

7 6

co 0

M

0

0 n

In

O N 0 0 A

N 0

10

0 0 v

N

O

N O

N N

6 6

0

AND .

OEST

0

0

0

5 4 3 2

0

L I I I I I l I I I 1 ;234567891 01 112

Day Fig. 1 . Daily incidence of bowing display by paired males subjected to different hormone treatments . Birds were paired for 30 min per day begining on day 1 . The scores represent the mean number of 2-min sub-periods during which the behaviour was recorded. See under methods for further details. Controls -•--, LH - - - p - - FSH -p-, androgen --- 9---,

I CONT.

L .H.

PROL.

PROG .

Fig . 3 . Mean incidence of driving (solid columns) and attacking (hatched columns) in paired males subjected to different hormone treatment . Notes as for Fig. 2,



292

ANIMAL BEHAVIOUR, 17, 2

appear as a response to bowing until later in the cycle (Table III) . Males tended to become more aggressive again towards the end of the cycle, but this was not associated with pushing from the female, as Fabricius & Jansson found for untreated birds; While the frequency of attacks was the same as in the controls, driving occurred rather more often (Fig. 3) . LH subjects differed from control birds in that bowing was more frequently followed by attacking (Table VII) . Follicle Stimulating Hormone. Males showed a marked increase in the total incidence of driving (Fig . 3), which in some pairs inhibited further progression of the cycle for several days . But the group exhibited a wide variation in responses so that while two pairs did distinctly more bowing and a third exceedingly more three pairs did not differ significantly from controls . This aggression lessened after a few days, but bowing again attained a high peak during the second week (Fig . 1), particularly in one pair ; this was not associated with pushing from the female (Fig . 4) . The usual response of the female to aggressive displays was to retreat, but sometimes to solicit (Table III) which then normally resulted in the male mounting (but not copulating) . Later in the cycle the female frequently bowed in response to the male's bowing causing a high incidence of this display (Fig . 2) . Periods of bowing, attacking and driving were of longer duration than in the controls : in bowing the call was louder and the up-and-down movements

more exaggerated, whilst during attacking the male often violently pulled the female's nape feathers and persisted in his attacks even though the female retreated . In these circumstances attacking and driving were not always easy to distinguish . Androgen . Males showed some increase in bowing in the early stages of the cycle ; this then decreased after the first 2 or 3 days (Figs I and 2) and thereafter was mostly confined to the opening of each observation period . But there was sufficient to cause a slight peak during the 2nd week and, as with LH and FSH, this was not the result of more pushing by the female (Fig . 4) . The frequency of attacking was similar to that of controls, as was driving (Fig . 3). One pair did very much more bowing, attacking and driving than the others . As with FSH, the duration of bouts of these displays and the persistence with which attacks were mounted was greater than in the control birds . Oestrogen . Males displayed little aggression (Figs 2 and 5) and bowing was mainly confined to the opening of each observation period . Attacking was reduced (Fig . 3) and did not occur at all after the first few days . In contrast females displayed a somewhat increased aggression, manifested by bowing (Fig . 2) and exhibited a degree of `maleness' absent from the controls and the females paired with the other hormone treated males .

Table III. Mean Number of Observation Periods in which Various Courtship Behaviours were Recorded Depending on Hormone Treatment of Males Begging Hormone treatment

Courtship feeding

a

Soliciting

Mounting Copulation

I

Y

a

Control

0.8

9 .8

7.8

0.8

11 .2

5 .0

0.0

3.5

LH

0.6

12 .8

10 . 4

0.8

7.8

2.2

0.2

1 .4

FSH

1 .7

9 .5

13 . 0

0 .0

7 .0

3.0

0.0

1 .5

Prolactin

0 .8

6.8

4.5

0 .0

3.5 (<0 .032)

3.0

0.0

2.2

Androgen

2.0

16 . 7

16 .2

3.5

6.2

3 .3

0 .0

2 .0

Oestrogen

0.0 (<0 . 05)

5 .8

9 .3

2.3

5.3

4 .2

0.3

1 .8

4.0

5 .3

7 .0

0 .3

0 .5 (<0 . 01)

0.5 (<0 . 05)

0 .0

0.3 (<0 . 05)

Progesterone

Figures in brackets give statistically significant 1-tailed probabilities calculate4 from Mann-Whitney U tests . Nonsignificant probabilities are not shown,



MURTON et al. : THE ENDOCRINE BASIS OF B1tEEDING BEHAVIOUR IN PIGEONS m v) O W O 0 0

CONT

L .H .

m 0 O N P O O

n

FS H

It O O O O 0 0

It

_p

~ m O O A

PROL. AND.

v

N

O N O O

OEST

v O O O

PROG.

Fig . 4 . Mean incidence of pushing in paired males (solid columns) or females (hatched columns) depending on hormone treatment of the males . Notes as for Fig. 2.

Day Fig. 5 . Daily incidence of bowing display by paired males subjected to different hormone treatments . Notes as for Fig . 1 . Controls -6---, prolactin - - - 0---, progesterone -o-, oestrogen --- 9--- . Prolactin . There was a marked similarity in behaviour between males treated with prolactin and progesterone . Under both hormones there was considerable variation among the individual

293

pairs, and bowing was considerably reduced when compared with controls (Figs 2 and 5), with little or no bow-call and a relatively small `dipping' action . With prolactin three of the six pairs were largely inactive for the first 5 days and even during the 2nd week produced only an initial bow at the start of each observation period. In one pair the male showed agonistic behaviour for the first few days (mainly bowing with an occasional brief attack) but subsequently little activity . The male of the fifth pair engaged in much bowing, attacking and driving for the first 3 days and then no activity for the next 2 ; in the 2nd week he gave only the initial bowing at the start of each observation period . The last male undertook considerable bowing, attacking and driving at the start of the first observation period, but only occasional bowing after this (this pair behaved very much like control birds throughout the cycle). It will be seen from Fig . 3 that, because only three males showed any tendency to attack, the frequency for attacking for the whole group is much lower than with control birds ; though driving seemed to occur more often the difference is not significant . The duration and persistence of all bowing, attacking and driving movements was low when compared with FSH treated birds . Progesterone . Three of the six males exhibited little sexual aggression (see p. 303) throughout the whole observation period apart from an occasional bow. Another male did some attacking on the 1st day and was then largely inactive until the 2nd week when attacking and driving (but not bowing) became very high in frequency . The male of the fifth pair engaged in much bowing, attacking and driving on the 1st day, but only weak initial bowing after that. In the last male there were periods of bowing, attacking and driving during the first 5 days (and no other activity), but only initial bowing during the 2nd week . Periods of bowing, attacking and driving were all of very short duration but, largely because of the behaviour of two males for which attacking and driving were particularly frequent, the overall incidence of both attacking and driving is high for the group (see Fig . 3) and appears similar to the FSH treated birds . This gives a false impression however, because the persistence of the attacks in no way compared with that shown under FSH treatment . Female responses. There was little evidence of aggression in the females with any of the hormone treatments with the exception of oestrogen where, as has been remarked, the females seemed





294

ANIMAL BEfAVIOUk,

to acquire a dominance not seen in the others. But there was a marked tendency for females to bow in response to the intense aggression of the males under FSH treatment and also partly to those males given androgen. It is not clear why such completely different male behaviour elicited bowing in the female . B. Begging, Courtship Feeding, Copulation and Displacement Preening Courtship feeding in controls was mainly confined to the early stages of the cycle (1st or 2nd day) . It was initiated by the female begging in response to displacement preening by the male, and was often repeated several times to form a sequence of behaviour, interspersed with begging by the female and displacement preening by both sexes and culminating with the female soliciting and the male mounting . Once nest demonstration became established, courtship feeding became rare and did not often occur more than once in each half-hour observation period (often near the start) . With most of the hormone treatments (Table III), courtship feeding was not particularly restricted to the first part of the cycle but occurred interspersed with other activity during most of the 2 weeks of observation, often in short bursts and not in repeated chains . Courtship feeding was often incomplete, being more like nibbling or `billing', food rarely being passed . Luteinizing Hormone. Courtship feeding rarely involved the passing of food and did not occur in long repeated sequences . Begging and soliciting were frequently ignored by the male, even though the female persisted in both these displays regularly (Table III) . There was a slight tendency for the males to lose some initiative to the females . Because the male so often ignored soliciting by the female, the frequency of both mounting and copulation was much reduced (Table III) . In the begging and courtship feeding sequences, displacement preening occurred in both males and females (but rather more in males) as in controls, but there was more displacement preening throughout the cycle not associated with courtship feeding behaviour. The actual incidence of displacement preening in females was the same as in control birds ; that of males was higher (Fig . 6) . Follicle Stimulating Hormone . The normal appearance of courtship feeding near the beginning of the cycle was not manifested, and although courtship feeding did occur frequently (Table III), the sequences were at first of short

17,

2

~tO N N

o v O N

9O

p N

N h V N

0O

0 0

0

0

0O A

0 0

35

~ M

M

O 0O

A

30

25

20

10,05F

A

59

PA

2 I CONT

L .H.

FSH

PROL . AND. OEST PROG .

Fig . 6. Mean incidence of displacement preening in paired males (solid column) or females (hatched column) depending on hormone treatment of male . Notes as for Fig. 2.

duration, and long ones did not appear until later. Similarly mounting and copulation were often late in appearing in the cycle . Once again begging and soliciting were frequently ignored by the male, but in one pair the male usually begged and initiated courtship feeding and tended to ignore the female when she begged . Displacement preening occurred in both sexes during the courtship feeding sequences, and there was an increase compared with control birds (Fig . 6), mainly because of the high incidence in the early stages when the male was still aggressive . Androgen. Courtship feeding normally appeared before nest demonstration except in one pair, for which there was no courtship feeding until the 5th day although the male nestcalled on the 1st day . Early courtship-feeding sequences were mostly of short duration, longer and more typical sequences appearing relatively late ; none the less the frequency of courtship feeding was high (Fig . 6 and Table VII) . Begging was frequently ignored by the male and this probably accounts for the large increase in females compared with controls (Table III) . Some of the males begged occasionally and



MtJRTON

et a!. :

THE ENDOCRINE BASIS O1F BREEDING $EHAVIOUR IN

two of them solicited fairly frequently . Displacement preening occurred throughout the cycle but, as in the controls, was mainly associated with courtship feeding . The increase in the amount of displacement preening over controls was, as with FSH, mainly owing to its high frequency during the early (aggressive) stages of the cycle (Fig. 6) .

Oestrogen . The males commenced nest demonstration very early so courtship feeding was reduced in these early stages, primarily because there was not a period of courtship feeding as a preliminary to nest demonstration . Later, courtship feeding became frequent (Table III), but apart from a few long sequences it was mainly confined to short bursts between nest demonstration. The frequency of begging and soliciting by the females was reduced when compared with controls (Table III), but there was not the tendency for either to be ignored by the males (as in some other hormone treatments) so that mounting and copulation were not significantly reduced . Soliciting by males was apparently increased (not statistically significant) ; indeed this was one aspect of their noticeable 'femaleness' . Furthermore, males often initiated courtship feeding. Early stage displacement preening activities were either reduced or absent, but they remained associated with begging and courtship feeding . It is likely that the reduction of agonistic tendencies in the males caused the low frequency of displacement preening in the females (Fig. 6) . Prolactin . Courtship feeding was comparatively infrequent (Table III) and on only four occasions were there long sequences . Two pairs did not engage in courtship feeding at all during the 2 weeks' observations ; one pair only attempted it once. Of the remaining three pairs, one showed some courtship feeding from the 9th day onwards (but got no further in the cycle than this, and was completely static by the last day) and the other two engaged in bursts of courtship feeding between nest demonstration during the 2nd week . Begging by the female was frequently ignored or led to nibbling and not proper courtship feeding ; soliciting and copulation were rare, except in one pair (Table III) . Displacement preening was not typically associated with courtship feeding, in fact, it was often absent at such times. Progesterone. Courtship feeding often appeared only as billing. In only one pair were there ever long sequences . In one pair courtship feed-

PIGEONS

293

ing was absent, and in two others it was confined to two brief billings in the 1st week and one short bout during the 2nd week respectively . Often courtship feeding was initiated by the males and the amount of begging from the females was reduced ; mounting and copulation were rarely observed (Table III) . The amount of displacement preening was much reduced and was less commonly associated with courtship behaviour (Fig. 6) . C. Nest Demonstration The frequency of nest demonstration in males over the observation period, for the six hormone treatments and the controls, is depicted in Figs 7, 8 and 9 . In the controls there was an increase during the first 5 days and a decrease during the last 5 days (days 1 plus 2 compared with days 5 plus 8 ; U = 4, P<0 . 05, 1-tailed : days 5 plus 8 compared with days 11 plus 12 ; U = 5 . 5, P = 0 . 05, 1-tailed). Not one of the hormone treatments follows this pattern . In all but the oestrogen-treated subjects there was a considerable reduction during the 1st week (severe suppression with progesterone and prolactin treatment) . During the 2nd week FSH and LH produced a pattern similar to the controls while with prolactin nest demonstration remained low in frequency. With androgen, however, although the total scores for the observation periods were similar to controls (Fig. 9), daily scores were consistently lower 1413 12 11 10 9

7 6

.

5 4

2 I 0

1 3

1

4

'

5

1 1 1 1 1 1 '

6

7

8

9

10

11

12

Day Fig. 7 . Daily incidence of nest demonstration by paired males subjected to different hormone treatments . Notes as for Fig . 1 . Controls --0 -, LH . . . o-, FSH --p-, androgen . . . 0---.



ANIMAL BEI#AVIOUk, 19, 2

206

Day Fig. 8 . Daily incidence of nest demonstration by paired

males subjected to different hormone treatments. Notes as for Fig. 1 . Controls-*-, oestrogen --- 0---, prolactin -0-, progesterone --- 0---.

v

N N

00

CONE

L .H .

h N O 00 V

N

rc

m o

N

Q M 00

O 00

FSH PROL .

AND.

g

o

0 N

0 0

M_ N 0 0

0 0

OEST PROG.

Fig. 9 . Mean incidence of nest demonstration in paired males (solid column) or females (hatched column) depending on hormone treatment of male . Notes as for Fig . 2.

during the first 5 days (days 4 plus 5, androgen compared with controls ; U = 7, P<0 . 05, 1-tailed) although nest demonstration was maintained at a high level during the last 5 days (Fig . 7) . Fig. 9 summarizes the incidence of nest demonstration by females, the daily pattern being similar to that noted for the males . Luteinizing Hormone. Nest demonstration occurred in all the pairs, but often consisted of wing vibration without squatting, and early in the cycle, was confined mainly to short periods of activity . It was frequently initiated by the females. The participants appeared unsettled so that nest demonstration failed to become well established (one pair went through a fairly normal sequence of events, resembling controls, during the 2nd week after remaining inactive for the first) . Follicle Stimulating Hormone. It has already been mentioned that increased aggression delayed the normal cycle with FSH. Even though nest demonstration sometimes appeared early in the cycle, it was usually wing vibration only and, in some cases was started by the female and not the male. During the 2nd week, nest demonstration became more normal in that squatting more often occurred, but was often intermittent, being interrupted by other behaviour patterns . The general behaviour of the birds was rather unsettled, as with LH . Androgen. The birds went through a fairly normal cycle after the initial bowing display period, though the transition from one behaviour pattern to the next was not absolutely clear . As with LH and FSH, the birds tended to be unsettled, so that sequences were not kept up for long periods . There was some resemblance to the controls in that nest demonstration normally followed after spells of courtship feeding and appeared fairly early in the cycle, but the males frequently engaged in nest demonstration for short periods only, and interrupted this behaviour by leaving the nest and walking around sometimes bowing, causing the display to be intermittent . Males retained a high level of dominance even when nest-calling so that females had difficulty in themselves starting nest demonstration on the nest bowl ; in one pair the female showed a marked reluctance to approach the male until the 9th day . In both males and females nodding and wing vibration tended to be common before true nest demonstration developed, but the males initiated the display at all times .

MUkTON et at. : THE ENDOCkt 1NB BASIS Op BItEDINCI BEIIAVIOUk IN PIGEONS

Oestrogen. As has already been stated, nest demonstration assumed great importance in these birds . From Fig. 8 it can be seen that during the first 5 days, the amount of nest demonstration was similar to that in the control birds . In the last 5 days nest demonstration was maintained at a level considerably higher than in the control birds (U = 4 . 5, P<0.05) . The male normally started nest calling early (1st or 2nd day) and persisted in this behaviour throughout the 2 weeks . At first the display was largely confined to the floor and only in the 2nd week did it become established on the nest . Females also engaged in much nest demonstration, but had great difficulty in shifting the males from the nest . When one bird of a pair was established on the nest, its partner spent much time in trying to get onto the nest or behaving in an agitated and irregular manner causing the time available for other displays to be reduced . Prolactin. Nest demonstration was generally suppressed. One pair did not engage in the display at all ; three pairs exhibited intermittent and weak nest demonstration during this time . In the last pair nest demonstration by the male started on the 1st day (after initial aggressive behaviour), was well established by the 3rd day and continued for the rest of the observation time (interrupted by bursts of courtship feeding) : practically no nest demonstration occurred in the female during the whole period . Most nest demonstration in all pairs consisted of wing vibration without squatting . Progesterone. The earliest record of proper nest demonstration was the 4th day ; previously only very slight wing vibration was noted . In two pairs it did not occur at all and in three pairs it took place only during the 2nd week . Nest demonstration was often just wing vibration, and was frequently undertaken away from the nest . It occurred in short spells punctuated by other activity . In the pairs where nest demonstration did occur, it was normally initiated by the male . D. Nibbling and Pushing Nibbling and pushing are normally closely correlated with nest demonstration . From Fig . 10 it will be seen that FSH and prolactin suppressed, while oestrogen increased the incidence of nibbling by females . A result that could not be anticipated was that FSH did not decrease nibbling by the male but androgen did have this effect during the first week (U = 7, P<0 . 05,

297

50

40

30

20

to

Fig. 10. Mean incidence of nibbling in paired males (solid column) or females (hatched column) depending on hormone treatment of male . Notes as for Fig . 2.

1-tailed) . Pushing by males was reduced by LH, progesterone and prolactin treatments. E. Twig Carrying and Nest Building In control birds twig carrying and nest building reached a peak shortly before egg-laying, after nest demonstration was well established in both sexes . Normally the male began by collecting twigs whilst the female was on the nest ; subsequently females also collected nest material . Both these actions were very much reduced with all hormones except FSH (Table IV) . As with control birds the accuracy of the figures for twig carrying and nest building is open to question owing to the continuous pairing of the birds for days 6 and 7 . Nevertheless, the figures do reflect the general trends of behaviour . Luteinizing Hormone . Twig carrying appeared earlier in the cycle than with the control birds and was started by the females who tended to do more than the males . The total incidence was much reduced as it also was for nest building which was seen only three times in all five males and not at all in the females . Follicle Stimulating Hormone. In five of the FSH treated pairs the pattern of twig carrying and nest building was similar to the controls during the 2nd week, although the amount was reduced . In one pair the male frequently engaged

ANIMAL BEHAVIOUR, 17, 2

298

Table IV. Mean Number of Observation Periods in which Nesting Behaviours were Recorded Depending on Hormone Treatment of Males Twig carrying

Nest building

a

y

a

y

a

y

Control

8.3

3 .2

7.8

5 .2

4.3

4.8

LH

1 .0

1 .8

0 .4 (<0 . 01)

0 .0

0 .2 (<0 .05)

1 .4

FSH

9 .8

1 .3

5 .0

1 .7

1 .3

3.5

Prolactin

1 .0

2.7

0. 3 (<0 .01)

0 .0

1 .5

0 .3

Androgen

0 .2 (<0 . 05)

1 .2

0.2 (<0 .01)

0.2

0.8 (<0.05)

1 .0

Oestrogen

0.8 (0 .05)

3.0

0. 7 (<0.01)

0.7

1 .0

2.5

0. 5 (<0 . 05)

0 .7

0 .2

0 .2 (<0 .05)

0 .8

Hormone treatment

Progesterone

0.0 (0 .001)

Moulding

Statistical probabilities as for Table II .

in twig carrying from the 2nd day onwards and also _did some nest building without any of the usual preliminary behaviour . The high figures for FSH seen in Table IV are partly due to the abnormal behaviour of this one male but even omitting these data the figures would still come closest to the control birds . Androgen. Nest building and associated behaviour was greatly reduced in these birds even though both sexes engaged in much nest demonstration behaviour. With only two pairs was there any attempt at true nest building (once by a male and once by a female) and two females were seen to manipulate twigs . The fact that the males tended to hold the nest position reduced their twig collecting activities. Oestrogen . Twig carrying by the females reached almost the same level as in the controls and was mainly confined to the 2nd week . In contrast, twig collecting by the males and nest building by both sexes was much reduced-the males being mainly engaged in nest demonstration. Prolactin. Nest building proper occurred only in one male, although one other male did some twig carrying during the 2nd week . Three females engaged in twig manipulation during the 1st week . The behaviour of one female was unusual, this being the bird whose partner started nest demonstration on the 1st day and maintained it throughout the 2 weeks . During the first few

days this female spent a considerable time manipulating and carrying twigs but this was not continued. Progesterone. Only one female attempted nest building on a single occasion . Three other pairs manipulated twigs a few times, but without the normal preceding behaviour. F. Other Activities Preening is to some extent a measure of nonactivity, and it was not much seen when birds were engaging in sexual displays . In individuals that were slow in starting their cycle or in which other displays were poorly developed, the amount of preening tended to increase (Fig . 11). Displacement preening was defined as the rapid touching of the scapulars without proper feather maintenance. Both types of preening occurred between bouts of aggression, for example, under FSH or androgen treatment . In general it was easy to distinguish between the two types, but there were occasions when prolonged bouts clearly started as displacement preening and developed gradually into true preening . Prolactin and progesterone reduced sexual activity, and in both these groups there was much standing with little activity . Yet, the progesterone treated birds showed no significant decrease of true preening (Fig. 11) but a significant decrease of displacement preening (Fig . 6), whereas the prolactin treated birds did not differ from controls in the amount of either kind of preening .



MURTON et at. : THE ENfSOCRIN$ PASTS OF DREMNG PPI4AVIOtJIt IN PIGEONS N rn N M 00

0 to O O

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Table V. Mean Number of Observation Periods in which Feeding and False Feeding were Recorded Depending on Hormone Treatment of Males Feeding Hormone treatment

False feeding

a

Y

a

Control

3.3

4.8

3.5

LH

8.6

18 . 8

3 .0 2-4

FSH

6.5

6 .8

3 .7

12 . 8

9.8

5 .5

5 .8

Prolactin

? 5 .2

1 .7 (<0 .05)

(<0-05)

Androgen

10 . 3

11-5

3-0

4-2

Oestrogen

7.2

8-7

2-5

4.2

14-5

9.5

1 .0

Progesterone

1-3 (<0 .05)

Statistical probabilities as for Table II . CO NT.

L .H.

FSH

PROL . AND .

OEST. PROG .

Fig. 11 . Mean incidence of true preening in paired males (solid column) or females (hatched column) depending on hormone treatment of male . Notes as for Fig. 2.

As displacement preening is frequently associated with courtship feeding, which was less often recorded in the prolactin treated subjects (Table III), it is at first difficult to account for displacement preening as the consequence of conflicting motivation. However, progesterone treated males engaged in much begging (Table III) as a preliminary to courtship feeding which could imply a more permissive role on the part of the male leading to greater compatability and a consequent reduction of conflict-this would be in keeping with the disinhibition hypothesis (see Hinde 1966) . Feeding, like true preening, was most apparent when sexual motivation was low . It will be seen from Table V that most of the hormonetreated birds fed more often than the control birds. When there were intermittent displays isolated from the normal sequence, the amount of feeding rose, as it also did when sexual activities were suppressed as under prolactin and progesterone administration . The high figure for females with LH-treated males is largely due to one bird which fed constantly during periods of non-activity in the 1st week . Pecking at food, which for convenience is called false feeding in the Tables, seems sometimes to have been displacement pecking (see

below), sometimes an intention to feed and sometimes an intention to collect twigs . Certainly it occurred most frequently as a preliminary to twig carrying and nest building, and in most groups the amount of food pecking was reduced compared with controls . With prolactin considerable food pecking occurred in association with feeding or when birds were otherwise inactive. Pecking occurred in aggressive situations (attack intention) or as intention to collect nest material. In most of the hormone treated groups there was rather more pecking than in the control birds (Table VI) . In the controls most pecking was done at twigs and was associated with twig carrying and nest building, but in the other groups there was rather more pecking not associated with these activities . With both LH and FSH there tended to be some pecking by either sex when its mate was nest demonstrating and this did not lead to twig collecting, and the same was true for the females of the oestrogen group . The high figure for males with FSH is partly caused by the single male who engaged in much twig carrying and nest building in the early stages of the cycle (see above) . With androgen, pecking was infrequent as was twig carrying and nest building . In the prolactin group most pecking was at twigs and was associated with nest building activities, but there was some aggressive pecking during the early stages not related to twig collection and which often occurred when the birds were otherwise inactive .



ANIMAL BEHAVIOUR, 17, 2

300

Table VI. Mean Number of Observation Periods in which Shutting and Pecking were Recorded Depending on Hormone Treatment of Males Strutting Hormone treatment

a

Control

2 .8

? 0 .5

LH

0.8

0. 6

5 .4

7.4

FSH

3 .0

1 .0

9.8

7.3

Prolactin

0.8

0 .0

3.0 (<0.05)

5 .7

Androgen

3 .7

1.3

3.0

2.8 (<0 . 05)

Oestrogen

1 .3

0.3

5 .0

0.0 (<0.05)

0 .0

9 .3

Progesterone

a

Pecking Y

5.5

6.2

17 . 0 (0 •0 01) 7.0

Statistical probabilities as for Table II. Strutting appeared to be a semi-aggressive display seen mostly in the male, either immediately before or after mounting, or after he had been pushed off the nest (Table VI) . Discussion The aim of the experiments was to help understand the natural behavioural cycle, particularly its dependence on specific hormonal states and to reconcile these with the histological condition of the testes. The results have been described in detail because a fair degree of complexity was encountered and other workers may well wish to re-assess our conclusions on points of detail . Males with inactive gonads do not normally respond to females with sexual displays or at least they show markedly reduced responses (Carpenter 1933a and b) and so hormone release must produce an appropriate internal state for the various sexual displays to be expressed . The exact mode of action remains enigmatic though hormones presumably often function by raising the excitability of the central excitatory mechanism (Beach 1942 ; 1944) . Whether the areas stimulated within the brain are so extensive as to involve the whole nervous system (Kawakami & Sawyer 1959) or whether hormones act on central nervous mechanisms specific for the behaviour pattern concerned (Tinbergen 1951) is not clear, though the latter view now seems outmoded . Lehrman (1955) and Hinde (1966) give evidence that some behaviour patterns may

depend more on interactions between neural centres and sensitized peripheral organs than on a direct origin and organization from neural centres . By electrical stimulation of specific points in the pre-optic nuclear complex, Akerman (1966) was able to induce characteristic motor components of the aggressive elements of the introductory bowing display and also nest demonstration, and produced different levels of integration depending on the site of stimulation. In the present experiments the various hormone treatments did not alter the normal sequence within any of the particular behaviour chains as defined by Fabricius & Jansson (1963) (see p. 289), although the different behaviour sequences could be truncated, manifested incompletely, or not at all . Thus a behaviour pattern such as copulation did not appear out of context following nest demonstration . On the other hand, hormone treatment clearly facilitated the expression of particular behaviour patterns, for example, oestrogen enhanced nest demonstration actions at the expense of aggression or sexual behaviour proper . In the normal cycle the different behaviour chains are not absolutely rigid, for example, bowing may be followed by attack or by nest demonstration though the various pathways which can be followed are each relatively stereotyped . Table VII demonstrates for some of the more important displays how hormone treatment increased the probability of a behaviour sequence following a particular pathway and it will be referred to below . The appearance of territorial behaviour, singing, sexual chasing and the initial male advance to the female leading to copulation, are generally considered to be strongly influenced by androgenic hormone . It is also generally considered that androgen release by the Leydig cells of the testicular interstitium is mediated by LH . Accordingly we expected that the behaviour of males treated with androgen would resemble that of normal subjects at the beginning of the cycle and that LH would give similar results, except possibly after a time delay . It was surprising to find that FSH produced all the elements of a heightened sexual-aggressive motivation and that LH was less effective in this respect . More precisely FSH, but not LH, significantly increased the incidence of driving (Fig . 3) . The causal factors involved in the bowing display seem to be those for attacking, fleeing and mating (Davies, in press) . Bowing, by combining submissive postures, seems to function as a ritualized appeasement display .



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ANIMAL BEHAVIOUR,

Thus tail fanning and head lowering may represent braking movements . It is to a large extent a conflict behaviour . FSH appeared to increase the sexual-aggressive component of the bowing display leading to more driving and strutting, while the fleeing component was reduced, that is there was an overall increase of sexual-aggressive chasing. The total frequency of the bowing complex was lower with LH (not statistically significant) but attacking more often followed bowing than in the other groups, including the control birds and those birds treated with androgen (Table VII) . Table VII shows, how the LH subjects exhibited a sequence running from bowing to attack, attacking then being followed by more bowing whereas under FSH attacking led noticeably to driving. This was also true for androgen treated birds which otherwise much resembled the control birds and progressed to the nest demonstration phase . In androgen subjects bowing was less often followed by attack than in those given LH (Table VII) . Thus androgen produced behaviour sequences most resembling controls in that there was a progression towards more sexual behaviour, FSH was less effective in that the aggressive components of the sexual displays were more pronounced which inhibited the full expression of courtship feeding, mounting and later nest demonstration, while LH made pure aggressive behaviour more noticeable . The results do not suggest that LH-mediated androgenic type behaviour and FSH seemed much more effective in this respect. The question arises of whether FSH is directly or synergistically responsible for behaviour of androgenic type and whether it facilitates the release of androgen from the Leydig cells . If FSH releases endogenous androgen it might also be reasonable to attribute the high aggressiveness of FSH-treated birds to the fact, that the endogenous androgen so released was more effective than exogenous testosterone proprionate . Current experiments with castrates should show whether FSH causes sexual behaviour in the absence of androgen . It will be noted below that androgen differed from FSH in allowing a much higher incidence of nest demonstration to develop (Fig . 9, Table VII) . It is of interest that LH (Mathewson 1961), but not testosterone (Davis 1957) will elevate the social rank of starlings Sturnus vulgaris. Similarly, Crook & Butterfield (in press) have shown that LH will elevate the rank order of Quelea . The absence of any marked direct influence of LH on, breeding

17, 2

behaviour would be consistent with what we believe to be its significance in the normal cycle . In seasonal breeding species like the mallard Anas platyrhynchos blood LH titres are high during the so-called refractory period if the birds are subjected to short photoperiods . At such times, although the pituitary-gonad axis cannot be stimulated to recrudesce by an increased photoperiod, the pituitary is not inactive and the new post-nuptial generation of Leydig cells is becoming charged with cholesterol positive lipids (Lofts & Murton 1968 and in prep.) . LH seems to feature in this post-nuptial rehabilitation of the interstitium at times when sexual behaviour is absent. It would have been surprising to find that any sexual displays were enhanced by LH because there would then have been some difficulty in accounting for their absence after the end of the breeding season, when LH titres may normally be high . Recent work in collaboration with Dr K . D . Bagshawe (in preparation) involving the radio-immunoassay of blood samples from pigeons killed during the bowing or nest demonstration phases of the breeding cycle confirms that virtually no LH is present, the method being extremely sensitive . Exogenous oestrogen produced a marked enhancement of the nest demonstration display of males (Fig. 9) with a reduction in aggressive elements as exemplified by a lowered frequency of bowing and even those partly aggressive displays like pushing which normally occur concomitantly with nest demonstration . Furthermore, nest demonstration followed bowing and other displays much more frequently in the oestrogen-treated subjects (Table VII). Oestrogen also caused a rapid collapse of the testis (with a dense build-up of lipids in the Leydig cells) so that it might be argued that oestrogen had its effects because it inhibited androgen release and enabled a freer expression of the less aggressive phase of the normal cycle (Lofts & Murton, in preparation) . That this is not the explanation is demonstrated by the high incidence of nest demonstration in the 2nd week following androgen treatment . It seems likely that in the normal cycle of the male there occurs an oestrogenprimed phase of behaviour, following the period of most active bowing and preceding or overlapping the phase of intensive nest-building . The nest demonstration display which contains many submissive elements, for example, wing quivering reminiscent of nestling food begging, the lowered head and body, certainly functions to attract the female to the crouching



MURTON et al. : THE ENDOCRINE BASIS OF BREEDING BEHAVIOUR IN PIGEONS male and the nest site he has selected (Murton 1962 ; Fabricius & Jansson 1963) . It is also very likely that the display has evolved by ritualization from the twig-fixing movements used in nest building especially as Goodwin (1956) has shown that in Geopelia humeralis the nod of the nest-calling male ends in the typical movement of a male fixing a twig into its nest . But oestrogen injection, though it facilitated nest demonstration, failed to increase the level of nest building (Table II) ; this is of interest in view of Lehrman's (1958) finding that exogenous oestrogen increased nest building in female ring-doves . However, Lehrman (1961) has reservations regarding the role of oestrogen on male nest building behaviour, and cites Noble & Wurm (1940) who found that in the black-crowned night heron only exogenous testosterone proprionate and not oestrogenic hormone would cause nest building . Warren & Hinde (1959) could only induce nest building in female canaries when they employed nearly lethal doses of the hormone . Fabricius & Jansson (1963) considered that the sight of the nest-calling female often stimulated the male to collect nest material and certainly this is the pattern in the normal cycle . Females at some stage showed a high level of nest demonstration in those groups where the males had been treated with oestrogen or androgen, without the males showing much inclination to collect twigs ; females also indulged in much nest demonstration in those groups treated with prolactin, LH and FSH, in which cases the males displayed more twigcollecting behaviour . Indeed, there was no obvious indication that nest demonstration in the female released twig collecting by the male . Only those males treated with FSH exhibited anything like a normal level of twig-carrying and nest-building activity, all other hormones including oestrogen resulting in a severe depression of this behaviour (Table IV) . FSH also increased the incidence of pecking which in this case, as already stated (p . 299), was an intention movement of twig carrying (Table VI), and this could imply that FSH features in nest-building behaviour in the normal cycle . If FSH does again become important at this stage of the cycle an increase in aggressiveness coincident with nestbuilding might be anticipated . Fabricius & Jansson have already pointed out that in the normal cycle there is a second peak in bowing and attacking (which above were attributed to FSH more than androgen) 3 days before egg laying when nest-building reaches a peak, They

303

infer that this was correlated with an increase in pushing by the female, but in fact, the male' often bows and attacks when the female is showing noticeable submissive posturing . In the brush, turkey the male does not permit the female near the nest mound during the most intensive phase of his building activities (Fleay 1937) . Nest-building is followed 2 to 3 days later by egg-laying and the onset of incubation . The importance of behaviour patterns during nestbuilding in causing oestrogen release in the female leading to ovulation needs no elaboration, Lehrman (1961) has summarized much work, including his own studies, which strongly suggests that the onset of incubation behaviour then depends on progesterone while experimentally exogenous progesterone induces ring-1 doves to incubate eggs placed in their nestbowls . Once incubation commences Lehrman considers that stimuli arising from the act of incubation or of seeing another bird incubate cause prolactin release, so that prolactin is a consequence and not the cause of incubation. Prolactin does facilitate parental care once young are hatched but the hormonal basis of incubation and of care of young are to be considered as quite distinct. The present study was not concerned with events beyond egg-laying but the gonadal and behavioural correlates at the onset of incubation are pertinent . Exogenous progesterone produced a state very reminiscent of pairs of birds which had recently lost their nest and eggs ; for instance, wood-pigeons Columba palumbus which have had their eggs destroyed will sit around in their territory, often with feathers raised and spend much time preening . The birds behave as a well-established pair, often coming close together with few signs of sexual activity . Progesterone has a very marked anti= gonadotropic effect and even more than oestrogen resulted in a rapid collapse of the testes . Yet the birds' behaviour differed from that of two non-reproductively active individuals put together, presumably as a result of the exogenous progesterone. Sexual behaviour was noticeably reduced both in the form of the partly aggressively motivated bowing display and with nest demonstration, where sexual motivation is stronger (Figs 2 and 9) . But, although nest demonstration was reduced in both males and females the incidence of nibbling (this was abnormal, see below) was - very high, this behaviour being typical of pairs showing a high degree of mutual tolerance, This is also



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reflected in the increased tendency for males to beg, even though the amount of courtship feeding was not above normal . In contrast, driving, which can be enhanced by FSH, was prominent (Fig. 3, Table VII) while attacking was maintained at a high level (Fig. 3, Table VII) and pecking increased (Table VI) ; pecking and attacking often occur in winter feeding flocks and at other stages of the cycle . Displacement preening which is indicative of a conflict in motivation was reduced (Fig. 6), whereas true preening was increased (Fig. 11) but not significantly so ; there was little pecking but much true feeding (Table V) . The results are in agreement with the studies of Vowles & Harwood (1966) . These authors found that certain aggressive and defensive movements, particularly pecking and charging (defined as an attack posture plus rushing by Miller & Miller 1958, and similar to driving in the present study), were enhanced by exogenous progesterone, but after some delay as if a second mechanism was activated . This aggression was most noticeable just before egglaying (when endogenous progesterone is supposed to be present) and again when the young hatched . Both prolactin and progesterone stimulated aggressive and defensive behaviour to a model predator but only progesterone maintained these same responses to other pigeons . Progesterone and prolactin are each considered to inhibit FSH activity. Consistent with this suggestion, bowing was inhibited by both these hormones. Attacking and driving were only inhibited by prolactin but as these displays may be specifically enhanced by progesterone there is perhaps no problem in accounting for the different responses . On the other hand certain sexual behaviour patterns like courtship feeding, nibbling and soliciting by males were less inhibited by progesterone than by prolactin, while some, notably begging, were more frequent in progesterone-treated subjects than in the controls . Nibbling appeared to derive from incomplete courtship feeding when the females did not respond to the males' begging . While the result looked like typical nibbling it apparently had a different basis to that normally associated with nest demonstration . The failure of the females to indulge in complete courtship feeding may well have depended on the males' failure to displacement preen, as this movement normally seems to signal the females' advance . Courtship feeding proper, begging by males and even soliciting were apparent following androgen injection (see above) . Thus it is con-

17, 2

ceivable that in blocking FSH, progesterone did not suppress the expression of androgenic effects . Consistent with this possibility the Leydig cells did not appear abnormal under progesterone treatment (in preparation) . Prolactin did appear to reduce androgenic-type behaviour and although the mechanism requires definition, it is consistent with the role of prolactin during later brood care . Prolactin also differed from progesterone in its effects on those displays occurring later in the normal cycle. Mounting and copulation were less inhibited by prolactin than by progesterone (Table III). Considering those females which did not lay eggs, Table II shows that follicle size and oviduct weights were lower in females paired with progesterone-treated males, than with males given prolactin, the differences being significant (p . 290) . The only really outstanding difference in the behaviour of the two groups of males was the absence of mounting and copulation in progesterone-treated birds . It therefore seems likely that these actions are specifically involved in stimulating follicle development (oestrogen from developing follicles would normally cause oviduct growth) . On the ethological evidence so far presented these displays appear during the `oestrogen' phase of the cycle and are not directly dependent on androgen or FSH . Histologically the testes of prolactin-treated males contained no tubular lipids so that FSH output and oestrogen synthesis in these had apparently been less affected than with progesterone. Summary 1 . The effects of repeated dosage with exogenous testosterone proprionate, oestradiol benzoate, progesterone, NIH .LH, NIH.FSH and prolactin on the pre-incubation behaviour of intact male Columba livia were investigated . The observation techniques and methods for quantifying the results were those used by Fabricius & Jansson (1963) and the subjects were paired with normal untreated females. 2. FSH enhanced the sexual-aggressive components of the bowing display, particularly driving, while LH increased the probability that attacking would follow bowing . Androgen produced a pattern more nearly resembling the controls in that the bowing display progressed towards the sexual manifestations of mounting, courtship feeding and nest demonstration . Prolactin inhibited bowing, driving and attacking but progesterone depressed bowing while allowing attacking and driving to be expressed,



MURTON et al. : THE ENDOCRINE BASIS OF BREEDING BEHAVIOUR IN PIGEONS

Progesterone also resulted in an increased incidence of aggressive pecking and a decrease of mounting and copulation, reflected in a failure of follicle development in the females . In general, exogenous LH had little influence on the normal cycle of paired birds. 3. Oestrogen suppressed the aggressive components of the pre-incubation displays, but markedly and consistently elevated the nest demonstration behaviour . All other hormone treatments inhibited nest demonstration, except that testosterone did allow it to develop normally in the second-half of the cycle. 4 . All hormone treatments, including oestrogen, inhibited twig collection and nest building but FSH differed from the other hormones, in that it allowed a nearly normal level of nest building, compared with controls, to develop . 5. Progesterone maintained the amount of true preening and suppressed displacement preening ; whereas prolactin-treated subjects did not differ from the controls in this respect . 6. The responses of the females to control and treated males are documented . 7. The implication of the various hormone treatments is discussed in relation to the normal behavioural-endocrine cycle of the pigeon . It is considered that the male pigeon undergoes a cycle which is successively dependent on a changing hormone basis. Initial courtship, in which aggressive components are much in evidence, depends on high FSH/androgen titres . This phase is followed by one in which oestrogen becomes dominant leading to nest demonstration . Oestrogen release from the testis tubules may be facilitated by androgen (although FSH may be needed for oestrogen synthesis) . At the end of the oestrogen phase of behaviour FSH seems to become more involved leading to nest building . This phase is then followed by progesterone secretion and the onset of incubation . Acknowledgments We thank Mr N . J . Westwood and Miss E . Dean who helped with the observations and are grateful to Dr J. H. Crook for critically reading our final manuscript and suggesting various improvements. Mr A. G . Jenson kindly prepared the text-figures . REFERENCES Akerman, B . (1966) . Behavioural effects of electrical stimulation in the forebrain of the pigeon . 1 . Reproductive behaviour. Behaviour, 26, 323-338 . Bailey, R. E . (1952). The incubation patch of passerine birds . Condor, 54, 121-13¢,

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Beach, F . A . (1942) . Central nervous mechanisms involved in the reproductive behaviour of vertebrates . Psychol. Bull., 39, 200-226. Beach, F . A . (1944) . Relative effects of androgen upon mating behaviour of male rats subjected to forebrain injury or castration . J. Exper. Zool., 97, 249-295 . Beach, F . A. (1948) . Hormones and Behaviour . New York : Harper and Brothers . Beach, F. A. (1951) . Effects of forebrain injury upon mating behaviour in male pigeons . Behaviour, 4, 36-59 . Bennett, M . A. (1940) . The social hierarchy in ringdoves . II. The effect of treatment with testosterone proprionate. Ecology, 21, 148-165. Carpenter, C. R . (1933a) . Psychobiological studies of social behaviour in Aves . I . The effect of complete and incomplete gonadectomy on the primary sexual activity of the male pigeon . J. comp . Psychol., 16, 25-96. Carpenter, C . R . (1933b). Psychobiological studies of social behaviour in Aves . II . The effect of complete and incomplete gonadectomy on secondary sexual activity with histological studies . J. comp . Psychol ., 16, 59-97. Collias, N . E . (1950) . Hormones and behaviour with special reference to birds and the mechanisms of hormone action. In A Symposium on Steroid Hormones (ed. E . S . Gordon), pp . 277-329 . Madison : University of Wisconsin Press . Davis, D . E . (1957) . Aggressive behaviour in castrated starlings. Science, 126, 253 . Davis, D . E. & Domm, L . V . (1941) . The sexual behaviour of hormonally treated domestic fowl . Proc . Soc . exp. Biol. Med., 48, 667-669 . Fabricius, E. & Jansson, A-M . (1963) . Laboratory observations on the reproductive behaviour of the pigeon (Columba livia) during the pre-incubation phase of the breeding cycle . Anim . Behav ., 11, 534-547. Fleay, D . H . (1937) . Nesting habits of the brush-turkey . Emu, 36, 153-163 . Goodwin, D . (1956) . The significance of some behaviour patterns of pigeons. Bird Study, 3, 25-27. Hinde, R. A . (1966) . Animal Behaviour . A Synthesis of Ethology and Comparative Psychology . New York and London : McGraw-Hill . Hinde, R . A . (1967) . Aspects of the control of avian reproductive development within the breeding season . Proc . XIV Int. Orn. Congr., Oxford . Kawakami, M . & Sawyer, C. H. (1959) . Neuroendocrine correlates of changes in brain activity thresholds by sex steroids and pituitary hormones . Endocrinology, 65, 652-668 . Lehrman, D . S. (1955) . The physiological basis of parental feeding behaviour in the ring dove (Streptopelia risoria) . Behaviour, 7, 241-286. Lehrman, D . S . (1958) . Effect of female sex hormones on incubation behaviour in the ring dove (Streptopelia risoria) . J. comp . physiol. Psychol., 51, 142145 . Lehrman, D. S . (1961) . Hormonal regulation of parental behaviour in birds and infrahuman mammals . In Sex and Internal Secretions (ed. W. C . Young), pp . 1268-1382 . Baltimore : Williams & Wilkins. Leonard, S. L . (1939) . Induction of singing in female canaries by injection of male hormone . Proc . Soc, exp . Biol. Med., 41, 229-23Q,



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Lofts, B . & Murton, R . K . (1968) . Photoperiodic and physiological adaptations regulating avian breeding cycles and their ecological significance . J. Zool. Lond., 155, 327-394. Mathewson, S . F. (1961). Gonadotropic control of aggressive behaviour in starlings . Science, 134, 1522-1523 . Miller, W. J . & Miller, L. S. (1958) . Synopsis of behaviour traits in the ring dove. Anim. Behav ., 6, 3-8 . Morris, D . (1954) . The reproductive behaviour of the zebra finch (Poephila guttata), with special reference to pseudofemale behaviour and displacement activities. Behaviour, 6, 271-322. Morris, D. (1955) . The causation of pseudofemale and pseudomale behaviour : a further comment. Behaviour, 8, 46-56. Murton, R. K. (1962). The functional basis of some behaviour in the woodpigeon Columba palumbus. Ibis, 104, 503-521 . Noble, G . K. & Wurm, M . (1940). The effect of testosterone proprionate on the black-crowned night heron. Endocrinology, 26, 837-850.

Shoemaker, H . H . (1939). Effect of testosterone proprionate on behaviour of the female canary . Proc . Soc. Exptl. Biol. Med., 41, 299-302 . Tinbergen, N . (1951) . The Study of Instinct. Oxford : Clarendon Press. Van Tienhoven, A. (1961) . Endocrinology of reproduction in birds . In Sex and Internal Secretions (ed . W. C. Young), pp. 1088-1169. Baltimore : Williams & Wilkins . Vowles, D. M. & Harwood, D . (1966) . The effect of exogenous hormones on aggressive and defensive behaviour in the ring dove (Streptopelia risoria). J. Endocrin., 36, 35-51 . Warren, R. P . & Hinde, R. A. (1959) . The effect of oestrogen and progesterone on the nest-building of domesticated canaries . Anim . Behav., 7, 209213 . (Received 25 January 1968 ; revised 10 July 1968 ; Ms. number: 800)