Social influences on reproductive physiology and ethology of budgerigars (Melopsittacus undulatus)

SOCIAL INFLUENCES ON REPRODUCTIVE PHYSIOLOGY AND ETHOLOGY OF BUDGERIGARS (Melopsittacus undulatus) BY

B. F . BROCKWAY*

Laboratory of Ornithology, Cornell University, Ithaca, N . Y.

Introduction

Lehrman, 1959) . For Budgerigars, not only is the presence of a nest box apparently necessary, but the spatial relationship between the nest entrance hole and perch seem similarly important . Unpaired females, able to see and hear each other, occupied suitable nest boxes and all given the additional opportunity to hear male vocalizations laid within 18 days of the experiment . Those unable to hear male vocalizations engaged in some next box occupation but did not lay within 30 days (Brockway, 1962a) and had only moderately developed ovaries and oviducts then . Thus, while interactions with a mate or suitable nest boxes are not a sine qua non for egglaying, the vocal presence of the opposite sex does stimulate female nest box behaviour . ovarian development and egg-laying (presumably through hypothalamic-hypopheseal action) in females provided with suitable next boxes under typical aviary lighting conditions . Further, the vocal and visual stimuli of other females, with about 14 hours of light per day when suitable nest boxes are provided or vocal stimuli of other females with 24 hours of darkness per day when nest boxes are not provided, do not appear to stimulate ultimately full ovarian development and oviposition in the absence of male vocalizations . So far, attention has been focused on reproductive stimulation of individuals by others such as a mate or possible mate, Ficken et al. (1960), using unpaired male-female combinations provided with suitable nest boxes, demonstrated that being able to see and hear or only hear other such combinations was associated with full ovarian development, egg-laying, and spermatogenesis ; whereas the gonad development of both sexes was significantly less in those male-female combinations isolated both visually and vocally from others . Presumably some social factor(s), in addition to the presence of a member of the opposite sex, a suitable next box, and the opportunity for interactions between the male and female of a combination is necessary for breeding in "isolated" situations . Pair formation, probably necessary for breeding,

Melopsittacus undulatus, a colonial, nomadic

parrot of the sub-family Psittacinae, inhabits the dry grasslands of Australia . Domesticated strains breed rapidly throughout the year and no seasonal cycles of gonad recrudescence or regression have been found (Brockway, 1962b) . It is common avicultural knowledge that pairs isolated from the sight and sound of others do not breed readily, if at all . Social stimulation of breeding has been investigated in other species of birds . Presence of a mate (Burger, 1942 ; Polikarpova, 1940), sight of another individual or self (Matthews, 1939), and presence of hormonally stimulated males (Shoemaker, 1939) have been shown to stimulate ovarian development and egg laying in Starlings (Sturnus vulgaris), House Sparrows (Passer domesticus), "pigeons", and canaries (Serinus canarius) respectively. Caging male Starlings with females seems to stimulate testis development (Burger, 1953) . Vaugien (1951) demonstrated that vocalizations of other Budgerigars stimulates ovarian development and egg-laying of females kept within dark boxes 24 hours a recognizes darkness as a stimulating factor perhaps simulating the lighting conditions inside the nest box . In support, I have observed that female Budgerigars, not provided with nest boxes under aviary conditions of approximately 10 to 14 hours of light per day and able to hear and see both sexes, do not lay nor are their ovaries well developed. Thus, in two situations, both possessing male vocalizations but differing in amount of light per day, only in Vaughan's "dark situation" did females lay . Although pairs caged together under the above aviary lighting conditions perform precopulatory behaviour and copulate, and males typically show live sperm upon milking (Brockway, 1962b), if such pairs are not provided with nest boxes, ovarian development is nil . Suitable nesting conditions are important for ovarian development and egg-laying in many other species of birds (Lack, 1953 ; Marshall, 1959 ; *Present address : Department of Zoology and Entomology, The Ohio State University, Columbus, Ohio . 493



494

ANIMAL BEHAVIOUR, XII,

may be hindered by the absence of other pairs . Perhaps members of "isolated combinations provide insufficient vocal or other reciprocal behavioural stimulation . To investigate these, the effects of only being able to see others, and the nature of interpair stimulation involved in breeding, the following study was made . Materials and Methods The Birds All the 11 to 2-year-old birds used had no known breeding experience . They were allowed to pair 3 days before the beginning of the study and then separated, being reunited when the experiment started . Gonads were examined by laparotomy and males milked for sperm (see Brockway, 1962b) just before pair formation . Only females with non-developed ovaries (ovocytes of 1 . 0 mm . or less in diameter) and males showing sperm upon milking were used . All milked sperm appeared motile when placed in a 0 . 85 per cent . sodium chlorine solution and did not stain with Nigrosin-eosin according to the method outlined in Lake (1954) . They were, accordingly presumed to be not dead sperm . Birds were fed ad libitum a diet consisting of French's Parakeet Seed, French's Conditioning Food, cuttle bone, quartz gravel and fresh water . Treatments Four situations were arranged with 4 pairs per situation : (1) those that could both see and hear others, (2) those that could only see others, (3) those that could only hear others and (4) those that could neither see nor hear others ("isolated" situation) . For the "see only" situation, 4 Hartshorne Sound Chambers* with glass windows were used . The parameters of visual contact were made identical for both (1) and (2) . The cages in both situations were arranged in a hollow square, each pair thus having the opportunity of viewing the other 3 in its situation . Cages in the "hear only" situation were separated by sheets of masonite . The "see and hear" and "hear only" cages were placed together in one room, giving each individual the opportinity to hear the same number of others . The "isolated" cages were placed in widely scattered rooms in another building . Cages in all situations were of identical size, provided with standard 64 x 6; x 91 *For details of construction contact Mr . James M . Hartshorne, Laboratory of Ornithology, Cornell University, Ithaca, New York,

4

inch next boxes having an entrance diameter of I I inches, and received 14 hours of light per day . Ninety days after this experiment started it was found that the nest hole entrance had been placed too low relative to perch level, thus inhibiting female nest box activities and egglaying (Brockway, 1962a) . So, entrances were raised at this time and the experiment allowed to run for another 30 days . The experiment was then repeated using different birds and suitable nest hole entrance heights . Both experiments were arbitrarily terminated when one-quarter of all females had laid . The first experiment lasted 120 days whilst the second took only 38 days . Obviously, both experiments are not identical and data from both were analysed separately . Some comparisons between the two, especially in items measured weekly, can be made ; and therefore results of both experiments are presented together where appropriate . Measurements All pairs were observed for 3 hours twice weekly . Sexual behaviour of both sexes, amount of male "Warble", and female nest box examinations and occupation (see Brockway, 1962a) were averaged per hour for each day of observation . Males were milked for sperm weekly during experiments . All gonads and accessory sex ducts were preserved in Bouins solution at the end of the experiments and examined later. Egg-laying was also recorded, Since some females laid and some did not, ovary and oviduct weights varied too much to permit analysis . Data were analysed by means of Analysis of Variance (Snedecor, 1956), Chi-square and Student's T test (Simpson, Roe & Lewontine, 1960) . Effects of sigh or sound were analysed by comparing the 2 experimental groups having the factor against the other 2 lacking it . The null hypothesis was rejected at a P (probability) level of less than 5 per cent . Results (1) Testes and Vasa Deferentia Tables la and lb show that the effects of sight of other pairs and sound of other pairs were significantly associated with heavier weights of both organs . Furthermore, any effect due to differences between the 2 experiments was insignificant . Results of weekly sperm milkings were roughly graded into 4 categories and assigned the following numerical values : (a) presence of milky white fluid plus sperm, 7 ; (b) presence of sperm with sparse clearer fluid, 5 ; (c) presence of sperm without visible fluid, 3 ; and



495

BROCKWAY : REPRODUCTIVE PHYSIOLOGY AND ETHOLOGY OF BUDGERIGARS Table Ia . Effects of Sight vs . Sound of Other Pairs on Testes Weights. No . of males

Mean wt. (mg.)

Situation Expt . I

Exp. 2

Exp . I

Expt. 2

Hear and see

4

4

293 . 9

268 . 4

Hear only

4

4

240 . 4

235 . 5

See only

4

4

193 . 6

184 . 3

!

I

732 I 4 86 . 5 I *Analysis of Variance. **Due to difference between the 2 experiments . ***Probability level .

No hear or see

p ***

Sight

5 . 83

<0 . 025

Sound

15 . 71

<0 .001

0 . 18

>020

Expt'l**

4 I

Effect

Table 1b. Effects of Sight vs . Sound of Other Pairs on Vas Deferens Weights . No . of males

Mean wt . (mg.)

Situation Exp . I

Exp.2

Exp .1

Exp .2

Hear and see

4

4

92 . 8

183 .2

Hear only

4

4

61 . 7

39 . 3

See only

4

4

43 . 4

41 .0

No hear or see

4

4

28 . 5

20 . 6

Effect 1

p ***

Sight

12 .62

Sound

20 .76

Expt'l * *

1

<0 .01 <0 .001

1 . 13

>0 . 10 I

*Analysis of Variance . * *Due to difference between the 2 experiments. ***Probability level . ;d) no sperm or fluid, 1 . All males with opportunity to hear others remained in category (a) throughout both experiments . Some males in "see only" and "isolated" situations continually failed to show sperm upon milking after the second or third week of either experiment . No male failing to show sperm at some time during either experiment showed sperm at any later time . Results for the sixth week of both experiments showed that the opportunity to hear others was significantly associated with high levels of sperm milking results, whereas the opportunity to see other pairs was not (see Table II) . Again, any effect due to difference between the 2 experiments was insignificant . (2) Male "Warble" This "chatter" so commonly associated with Budgerigars is performed mostly by males and consists of predominantly Loud Warble plus Soft Warble . Both vocalizations are described by Brockway (1962b) . No bird not having performed Loud Warble was ever heard to do Soft Warble, but the reverse often occurs . This is

important for when some individuals are loud warbling, it is virtually impossible to hear any soft warbling being done in a nearby cage . Therefore collective "Warble" was measured and this because : (A) it was the only vocalization group whose amounts differed notably among experimental situations and, (B) Loud Warble is mimetic in nature (Brockway, 1962b) . How much "Warble" each female had the opportunity to hear is presented in Table III . Females in the "see and hear" and "hear only" situations had opportuniies to hear roughly 23 minutes "Warble" per hour . In the "see only" and "isolated" situations, cages must be separately considered . Females in 2 "see only" cages could hear roughly 9 minutes per hour of "Warble" ; while the other 2 were presented with roughly 0 . 3 minutes per hour of "Warble" . In the "isolated" situations, females were presented with roughly 0 . 55 to 0 . 01 minutes per hour of "Warble" . Only among those males performing mean bouts of 9 minutes per hour or more, were any found to perform extensive precopulatory behaviour and show sperm upon milking .



496

ANIMAL BEHAVIOUR, XII, 4 Table H. Effects of Sight vs. Sound of Other Pairs on the Presence of Sperm .* No . of males Exp . 1

Situation

Mean Sperm Index**

Exp. 2

Exp . 1

Exp . 2

P ****

Effect

Hear and see

4

4

6 .5

7 .0

Sight

2 . 90

>0 . 20

Hear only

4

4

6 .5

7.0

Sound

26 . 17

<0 . 01

See only

4

4

3 .5

5.5

4

4

2 .0

2.5

1 . 72

>0 .20

No hear or see

Expt'l***

j *Analysis of Variance . **Milky fluid plus sperm, 7 .0 ; clearer fluid plus sperm, 5 .0 ; only sperm, 3 . 0 ; and no sperm, 1 .0 . * **Due to difference between the 2 experiments . ****Probability level . Table III . Amount of Male "Warble" Heard by Paired Females .* Pairs able to see and hear others

All females heard a mean of 23 . 21

Pairs able to hear others only

All females heard a mean of 23 . 21

Pairs able to see others only Cage

Mean

1 2 3 4

9 . 91 9 . 10 0 . 07 0 . 58

Pairs able not to hear or see others -

Cage

Mean

1 2 3 4

0 . 03 0 .08 0 . 55 0 .001

*Mean amounts in minutes per hour for total experiment .

(3) Other Male Precopulatory Behaviour Besides "Warble", the male precopulatory repertoire consists predominantly of Nudging the female's bill, (head) Pumping to, Billhooking, head bobbing to, feeding and attempting to mount her . These are interspersed with one another as also with sidling toward and away from her on the perch . (For a more complete description and discussion of precopulatory behaviours, see Brockway, 1962b) . Amounts of Nudging and Nudging-Pumping (these apparently function to increase the tendency of females to solicit for or allow copulation) were measured per male per hour for the duration of both experiments . NudgingPumping is performed by males with greater sexual motivation than is Nudging ; as measured by the degree of persistence in the face of repeated thwarting and the amount of subsequent mounting attempts . Only the second experiment with suitable nest entrance-perch relationships will be discussed here, although the general pattern is identical for both experiments . While only the effects of the opportunity to hear others is significantly associated with more Nudging per hour (see Table IV), both the

effects of seeing and those of hearing other pairs are significantly associated with the more sexually motivated precopulatory displays (see Table V) . A sharp line of demarcation exists between individual means of more than 3 or less than I male precopulatory action per hour throughout the second experiment and the first 6 weeks of the first experiment . To make the relative effects of each situation upon male precopulatory behaviour more meaningful, the number of males performing extensive precopulatory behaviour (more than 3 actions per hour) in each of the four situations of both experiments is considered . Of 8 males per group, 7 in the "see and hear" situation, 6 in the "hear only" situation, and only 3 in the "see only" situation performed extensive precopulatory behaviour. No males in the "isolated" situation did so . There was no difference (P level greater than 30 per cent .) among the total amounts of extensive precopulatory behaviour per hour per male in the first 3 situations . (4) Female Receptivity (Table VI) . This involves female response to extensive male precopulatory behaviour and is numerically



BROCKWAY : REPRODUCTIVE PHYSIOLOGY AND ETHOLOGY OF BUDGERIGARS

497

Table IV . Effects of Sight vs . Sound of Other Pairs on Male Precopulatory Nudging* . Number of males

Mean number of nudges/hr. * *

4

1 . 65

Hear only

4

1 . 19

See only

4

1 . 06

No hear or see

4

0 . 39

Situation Hear and see

I I

I "f"

P ***

Sight

3 . 97

>0 . 10

Sound

6 . 08

>0 . 15

Effect

*Analysis of Variance . **Logto of Nudges per hour + 1 .0 . ***Probability level . Table V. Effects of Sight vs . Sound of Other Pairs on Male Precopulatory Nudging-Pumping. I

Number of males

Mean number of Nudge-pumps/ hr .**

Hear and see

4

1 . 13

Sight

4 . 88

<0 . 05

Hear only

4

0 . 64

Sound

10 . 13

<0 . 01

See only

4

44

No hear or see

4

Situation

P ***

Effects

0

*Analysis of Variance . * *Logio of Nudge-Pumps per hour + 1 . 0 . ***Probability level . Table VI. Effects of Sight vs. Sound of Other Pairs upon Female Receptivity (M .S .C.) 1 and Related Behaviours per hour2 . Experimental situations See and hear others Behaviour

No.*

Mean SE**

Only see others Mean SE**

No .* I

Female M .S .C . Total male precop . Copulation

1

Only hear others No.*

Mean SE**

1 . 5-0 . 30

6

0 . 68+0 . 14

7

0 . 51±0 . 13

3

7

12 . 6+1 . 9

3

8 . 6+0 . 9

6

11 . 7+1 . 2

7

0 .08+0 . 03

3

0 . 61+0 . 38

6

0 . 15_0 .07

-

1-M .S .C . is index of female receptivity . It is the sum of the number of times she solicited for copulation, allowed male mounting or copulation . 2-Experiments lasted 6 weeks . Weekly amounts per hour were added and the sum divided by 6 . *-Number of pairs in which male performed extensive precopulatory behaviour . See text for explanation . **-Standard error of the mean . represented by the number of times each female significantly lower than those for females in the solicited plus the number of times she allowed "see only" situation . No difference exists among her mate to mount or copulate with her per these situations in hourly amounts of male hour . No difference was found (P level greater precopulatory behaviour. No female whose mate than 25 per cent .) in mean acts of female recep- did not perform extensive precopulatory betivity per hour between females in the "see and haviour was observed to solicit for or allow hear" and the "hear only" situations . Female recopulation . Further, "see only" pairs copulated more often than either the "hear only" or "see ceptivity values for both situations in which the and hear" pairs . female and her mate could hear other pairs are



498

ANIMAL BEHAVIOUR, XI ,

(5) Female's Nest Box Activities The importance of measuring this behaviour is that under conditions of 14 hours of light per day, as in this experiment, no female has been observed to lay without prior behaviour concerning the nest box . Females begin nest box examinations about 2 weeks prior to laying by approaching and looking inside the nest entrance hole . The amount of time spent with her head inside the entrance increases with subsequent visits . Presently, she crawls inside the nest box in the course of her entrance investigations . At first, she remains inside the box only for a brief time (typically a matter of seconds) but, on subsequent trips, she tends to remain inside the box for increasingly longer periods . Laying females typically spend at least 30 minutes per hour inside the next box during the last 5 or so days prior to the laying the first egg . No female in "isolated" situations of either experiment was seen to occupy or investigate a nest box . The second experiment, with suitable nest hole entrance heights is analysed by means of a Chi-square test and the results presented in Table VII . The effects of being able to hear other pairs are not, whereas the effects of being able to see other pairs are, associated with greater performance of all 4 arbitrarily designated levels of female nest box activity presented in Table VII . (6) Egg-laying Two females in the "see and hear" situation, and 1 female each in the "hear only" and "see only" situations laid prior to termination of the

second experiment. There was no significant difference among these regarding the date of the first egg. Discussion Female's nest box activities, full gonadal development and subsequent egg-laying can occur independently of male and female precopulatory interactions and vice versa (Brockway, 1962a, 1962b) . As both copulation and oviposition must occur for successful breeding, it is notable that both above described categories including male gonadal development seem potentiated most by the opportunity of pairs to hear and to a lesser extent see others . That hearing vocalizations of males other than the mate is not a sine qua non for female gonadal development, oviposition and precopulatory behaviours can be seen from data on "see only" pairs . However, neither are vocalizations of a mate requisite for these (Brockway, 1962a) . But, it must be emphasised that male vocalizations from one source or another do seem a most important stimulus for these female activities. Failure of females of "isolated" pairs to lay when provided with suitable nest boxes may be because they had little opportunity to hear male "Warble" ; they certainly had the opportunity to hear other vocalizations . Further, since males of "isolated" pairs performed little or no visible precopulatory behaviours, their mates were not stimulated to perform such or be sexually receptive . Social stimuli (visual and/or vocal) of other pairs may exert its primary effects on the male

Table VII. Effects of Sight vs . Sound of Other Pairs upon Female's Nest Box Activities.

I

No . of females in each situation performing any level of activity (total N per situation= 4) Effect

Type of activity I

See and hear

See only

Hear only

No see --or hear Sight

Examination

4

4

3

0

F <0 .025

P <025

Occupies box less than 5 min ./hr .

4

3

2

0

<0 . 025

<0 . 25

Occupies box less than 30 min ./hr .

4

3

2

0

<0 . 025

<0-25

Occupies box more than 30 min ./hr .

3

2

1

0

<0 . 05

<0 . 5

No . females laying during Exp. 2

2

1

1

0

I

Sound

*No female has been observed to lay in the presence of nest boxes without performing all levels of next box activities . **By means of Chi-square tests,



BROCKWAY : REPRODUCTIVE PHYSIOLOGY AND ETHOLOGY OF BUDGERIGARS of a pair, resulting in a certain amount of vocalizations presented to a female both by other males and her mate . These may, in turn, somehow stimulate the secretion of male pituitary gonadotrophins promoting directly testicular activity and indirectly vasa deferentia development, and stimulate males to present their mates with other behavioural stimuli leading through mutually stimulating intra-pair interactions to copulation while also promoting female gonadal development and nest box activities . In view of this, let us discuss certain of these factors further . The opportunity to hear other pairs stimulates paired males to perform "Warble" . The mimetic nature of Loud Warble suggests that such interpair auditory stimulation may well be Loud Warble itself. The sight of other pairs seems, to a lesser extent, also to stimulate given males to perform "Warble". The increased variation in amounts of "Warble" per hour among males able only to see other pairs may well reflect the individual variation in the tendency to perform such, exaggerated by a stimulus of lesser impact than hearing the vocalizations of others . It is also possible that performing "Warble", or other vocalizations, may stimulate a male somehow to perform more . A mean of 9 minutes or more of "Warble" by males of pairs in any situation is associated with heavier testes and vasa deferentia, continued sperm production (or availability upon milking) and the performance of extensive visible precopulatory behaviour, as compared with those (2 males in the "see only" and 4 in the "isolated" situations) warbling less . However, no cause and effect relationship among any of these can be as yet claimed . While fewer males of pairs only able to see others performed extensive precopulatory behaviour, those so stimulated (by whatever means and mechanisms) performed just as much as those males in the experimental situations involving the opportunity to hear other pairs ; somewhat akin to a gross "all or none" response. Members of "isolated" pairs engaged in courtship feeding and reciprocal preening (activities tending to cement the pair bond) as did pairs in all other situations, but males infrequently performed precopulatory behaviour . The small amount performed was of types typical of low motivation and occurred mostly during the first week of both experiments . Since all males had the opportunity to see and hear others prior to both experiments, these pre-

499

copulatory activities by males in the "isolated" situations may have been a carry-over from preexperimental conditions . A high index of female receptivity, it might be argued, may reflect a superabundance of female solicitations per hour resulting from a lack of her mate's copulating with her . Thus, a female whose mate was more sexually motivated might show a lower receptivity index than one with a less sexually motivated mate . That such is probably not unduly influencing the indices used in this study is supported subjectively by behavioural observation and objectively borne out by the higher number of copulations per hour in the "see only" situation than in either of the other 2 situations . Also, the amount of male precopulatory behaviour per hour was not significantly different among the situations, indicating a relative "equality" among all males here . Soon I hope to be able to objectively "weigh" the various male precopulatory displays according to relative sexual motivation, thus permitting finer analysis . These data suggest that not being able to hear other pairs is most propitious for female re ceptivity to male precopulatory behaviour ; as if the vocalizations of other pairs somehow inhibits female sexual behaviour to some degree . Why, is presently unknown but females in the situations involving more natural conditions (the opportunity to hear or to hear and see others) did solicit and copulate with their mates . Since more males appear to be stimulated to perform extensive precopulatory behaviour by the opportunity to hear other pairs, this might perhaps help in the long run to offset any decreased female receptivity . In the "see only" situations, females soliciting for, or participating in, copulations were paired with those males having the heavier sex organs, performing extensive precopulatory behaviour and more than 9 minutes per hour of "Warble" . Such auditory stimulation from a mate may play an important role in stimulating reproductive activities of both pair members and it would be interesting to assay the relative effects of auditory stimulations versus that of visible precopulatory activities upon the sexual development of females. Unfortunately, it is currently impossible to examine the latter without the former . Female's nest box activities seem also socially influenced . Whether the experimental results . showing that sight is a greater stimulus than hearing of others, are due to small sample size, to the stimulation provided by being able to see



500

ANIMAL BEHAVIOUR, XII, 4

other pairs or indirectly in that females with less initial "interest" in the box are stimulated by seeing females with more initial "interest" is unknown at present . However, nest box examinations by one female seem to mimetically induce such behaviour in another ; and most nest box activity occurs with females able also to hear male "Warble" . In addition to the stimulus that male vocalizations have upon female's nest box activities, these vocalizations together with the darkness of the box within which she spends much time prior to laying possibly exert great effects on her gonadal development and oviposition . In conclusion, aside from species typical sight and sound having important functions in the reproductive biology of this species, they also seem to have marked differential effects on the sexes . Summary The statements below are restricted to heterosexual pairs of domesticated strains provided with suitable nest boxes under the conditions of this study unless otherwise stated . 1) The effects of being able to hear the Loud Warble of other males appears to stimulate males to warble more than they would otherwise . This also seems to stimulate, or be associated with, continued sperm production (i .e . availability of sperm upon milking) and oviposition . (2) The effects of being able to see or being able to hear other pairs are associated with significantly heavier testes and vasa deferentia . (3) The opportunity to hear large amounts of warbling from other pairs seems to inhibit female receptivity to male precopulatory behaviour, as measured by the number of times females solicited for or engaged in copulation per hour. The opportunnity to hear other males warbling seems to stimulate more males to perform extensive precopulatory behaviour, thus, perhaps, in the long run helping to offset the decreased female receptivity also produced . The opportunity to see but not hear others appears to stimulate reproductive activities in both members of a pair as compared to neither being able to see nor hear others . The opportunity to hear other pairs seems more stimulating in this regard than being only able to see other pairs. (4) The opportunity to see other pairs appears to stimulate female's nest box activities ; however, the opportunity to see and hear other females is less effective in unpaired females than

also being able to hear male vocalizations . The opportunity to see others seems more stimulating to all reproductive activities than not being able to see or hear other pairs . Acknowledgements I am greatly indebted to Drs . A . van Tienhoven and W. C . Dilger for invaluable advice and help during the course of this study ; and also to Drs . Dilger, S . L. Leonard, R . E. Phillips, A. P . Brockway and J . Edwards for reading and valuable criticism of the manuscript . I also want to thank Mr . James Hartshorne for providing the information on, modifying the design of and helping me with the sound chambers used . Thanks are also due the R. T . French Co . of Rochester, N .Y., for generous provision of birds . This study was aided by grants from the American Museum's Frank M . Chapman Memorial Fund and from the Sigma Xi-RESA Research Fund . REFERENCES . Brockway, B . F (1962a) . The effects of nest-entrance positions and male vocalizations on reproduction in Budgerigars . The Living Bird, First Annual of the Cornell Laboratory of Ornithology, 93-101 . Brockway, B. F . (1962b) . Ethological studies of the Budgerigar (Melopsittacus undulatus) . Ph .D . Thesis Cornell University . Burger, J. W . (1942) . The influence of some external factors on the ovarian cycle of the female Starling . Anat. Rec ., 84, 518 . Burger, J . W . (1953) . The effect of photic and psychic stimuli on the reproductive cycle of the male starling, Sturnus vulgaris . J. exp . Zool., 124, 227-239 . Ficken, R . W ., Tienhoven, A . van, Ficken, M . S . & Sibley, F . C. (1960) . Effect of visual and vocal stimuli on breeding in the Budgerigar (Melopsitacus undulatus) . Anim . Behav ., 8, 104-106 . Lack, D . (1933) . Nesting conditions as a factor controlling breeding time in birds . Proc . zool. Soc ., Lond., 106,231-237 . Lake, P. E . (1954) . The relationship between morphology and function in fowl spermatozoa . Proc . 10th World Poultry Congress, 79-82 . Lehrman, D . S . (1959). Hormonal Responses to external stimuli in birds. Ibis, 101, 478-496 . Marshall, A . J. (1959) . Internal and environmental control of breeding . Ibis, 101, 456-478 . Matthew, L . (1939). Visual stimulation and ovulation in pigeons . Proc. roy . Soc ., Lond., B., 126, 557-560 . Polikarpova, E . (1940) . Influence of external factors upon the development of the sexual gland of the Sparrow . Cited in : Lehrman, D. S . (1959) . Hormonal responses to external stimuli in birds . Ibis, 101, 478-496 .

Shoemaker, H . H . (1939) . Effect of testosterone propionate on behavior of the female canary . Proc. Soc. exp . Biol . Med., 41, 299-302 .



BROCKWAY : REPRODUCTIVE PHYSIOLOGY AND ETHOLOGY OF BUDGERIGARS Simpson, G. G ., Roe, A . & Lewontin, R . C . (1960) . Quantitative Zoology . New York : Harcourt Brace Co. Snedecor, G . W. (1956) . Statistical methods. Iowa State University Press, Ames . Vaugien, L. (1951) . Ponte induite chez la Perruche

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ondulee maintenue a l'obscurit6 et dans l'ambience des voliPres . Comp. rend. Acad. Sci., 232, 17061708 . (Accepted for publication 10th August, 1964 ; Ms . number : 472) .