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The performance of nest building by domestic hens: is it more important than the construction of a nest?
Anim. Behall., 1989,37,210-214
The performance of nest building by domestic hens: is it more important than the construction of a nest? B. 0. HUGHES, I. J. H. DUNCAN & MARGRETTA AFRC Institute of Animal Physiology and Genetics Research, Edinburgh Midlothian EH25 9PS, U.K.
F. BROWN Research Station, Roslin,
Abstract. Domestic hens were presented with three different types of littered nest: a flat litter surface (A), a preformed hollowed nest (B) and a preformed nest with an egg (C). Nests B and C had been previously constructed by the hen under test. The overall duration of pre-laying behaviour was greater in nest type C than in both nest types A and B. Of the three nest-building behaviour patterns, gathering, in which the hen moved litter nearer to her body with head and beak movements, and litter-placing, in which she picked up particles of litter and dropped them over her shoulder, increased in the preformed nests compared with the control. Rotating, in which the hen crouched on the nest, rotated and scraped outwards with her feet, did not differ between treatments. Thus, nest-building behaviour was not inhibited by the existence of a preformed nest. This finding does not support the hypothesis that animal welfare in intensive housing can be safeguarded merely by providing that environment which would have been created by the animal’s own activities. Rather, it suggests that performance of behaviour can in itself be reinforcing and that provision is required for such behaviour to be carried out. This finding may also have important implications for general motivational theory.
The concept of behavioural ‘need’ (the notion that animals’ welfare may suffer if they are unable to carry out particular behaviour patterns) was first set out in the report of the Brambell Committee (Command Paper 2836 1965) very much under the influence of W. H. Thorpe. The concept has since received a good deal of attention and criticism from applied ethologists, who have generally regarded it as having merit and utility, but requiring to be placed on a much more secure scientific footing (for example, see Dawkins 1983; Duncan 1987; Hughes & Duncan 1988). It has been enshrined in the European Convention on Animal Welfare and is one of the U.K. Farm Animal Welfare Committee’s objectives as providing animals in intensive husbandry systems with the ‘freedom to perform most normal patterns of behaviour’. The concept that the performance of behaviour, per se, may be important to animals has been questioned by Baxter (1983). He has postulated that behaviour, in this context, serves two main functions. (1) It contributes to biological fitness and, in domestic animals, to productivity. (2) It returns, through its functional consequences, the animal’s control system to a homeostatic set point and thereby switches off motivation. For welfare to be achieved, behavioural control 0003-3472,'89/020210+05$03.00/0
systems should remain at, or be allowed to return to, their set points. However, welfare is often at risk in intensive conditions because animals have not evolved in these environments and there is therefore a mismatch between the control system and the environment. Baxter (1983) gives appetite as a possible example. Many animals housed over long periods in intensive environments with access to food ad libitum become obese; this may be because the animals have not adjusted to the lower maintenance requirements so the set point for satiety is now at an inappropriately high level. Baxter (1983) then goes on to argue that, in relation to point (2) above, animal welfare in intensive environments may be safeguarded just as effectively by providing animals with the functional consequences resulting from the behaviour which they would have performed, rather than allowing them actually to perform the behaviour. He cites, as an example, nest building in sows, Sus scroja. The nest serves a number of functions, providing insulation, warmth, softness and protection for the piglets and support and cushioning for the udder of the sow. If all these functions could be provided by an artificial nest for sows then, Baxter argues, the sow would not be motivated to build a nest and the behaviour would not occur. One of the problems with Baxter’s hypothesis is
X‘ 1989 The Association for the Study 210
of
Animal Behaviour
Huglws et al.: Nest building !I!> domestic hens that it is difficult to disprove. Even if an artificial nest, believed to meet all the functions specified for the natural nest, was constructed but the sow continued to display nest-building behaviour, one could not state with certainty that the hypothesis had been disproved. It might be that the natural nest served other functions, as yet unidentified. which were not met by the artificial nest. However, the domestic fowl, Gullus gal/us domesticus, provides a particularly suitable model to examine this question. The hen, housed under semi-intensive conditions, with access to an approcomplex priate substrate, shows a relatively sequence of pre-laying behaviour and builds a new nest each time she lays an egg. This nest, though generally rudimentary, is built in a similar location time after time, often using the same materials (Wood-Gush 1975). Because many hens lay a long series of eggs on successive days it is easy to collect data, in contrast to sows, which farrow only two or three times per annum. In particular, the nest built by the hen herself on one day can be presented to her again on the following day, when it should more fully meet her requirements than it did originally. The experiment described in this paper was designed to test the hypothesis that the proximate function of nest-building behaviour is to construct a nest suitable for egg laying. The null hypothesis was that hens would display a similar pattern of nest building and pre-laying behaviour, regardless of whether they were presented with a featureless area of litter or with a preformed nest. Because it is not certain what a hen would regard as a preconstructed nest site, they were offered on separate occasions both a preformed empty nest and a preformed nest containing one egg.
MATERIALS
AND
METHODS
The 12 hens were 40-week-old ISA Browns (medium hybrid brown egg layers) which had all previously taken part in an experiment on nest-site selection and had subsequently been housed for some weeks in single battery cages, so were experienced in laying in a number of different types of nest site. About a week before each bird was tested she was placed with two others in a pen (2.4 x 2.4 m) with a littered floor, food hopper, drinking trough and littered open nestbox in order to accustom her to the type of environment in which
211
she would be tested. Most hens laid in the nestbox provided; any that did not were picked up while displaying pre-laying behaviour and placed gently in the box so that they became used to laying there. The test-pen was next to the home-pen and was of similar dimensions. It had a painted concrete floor and a nest site in the corresponding corner to that occupied by the nestbox in the home-pen. The nest site was an open wooden box (0.39 x 0.39 m with sides 0.10 m high) filled with wood shavings similar to those in the nestbox in the home pen. This site met the criteria set out by Appleby & McRae (1986) for a minimal nest site. A video camera was mounted in another corner of the pen and all behaviour displayed on the nest site was recorded for later analysis. The test-pen into which the hen was placed contained the nest site in one of three states which comprised the three treatments. In treatment A the box contained wood shavings levelled out to form a relatively flat surface about 6 cm below the top of the sides. In treatment B the box contained a nest previously constructed by that particular hen on an earlier occasion, often, but not always, on the previous day. The nest typically took the form of a hollow with a raised rim consisting of a mixture of wood shavings and feathers. In treatment C the box contained a nest previously constructed by that hen together with the egg she had laid in it (C). The presentation of nests took the form of a 3 x 3 Latin Square design with three hens being presented with all three types of nest in turn and in a different order. Only one nest of one type was presented to a hen on any one day. On occasion, the test ended sufficiently early for a second hen to be tested later on the same day. The hen’s laying record in her home-pen was monitored and on a test day she was placed in the pen at least 2 h before her expected time of lay, though sometimes the elapsed time before oviposition proved to be much longer. This period had to be considerable in order to avoid the possibility that she had already begun to display pre-laying behaviour in the home-pen. The experiment was carried out in four blocks, with each of the three hens in each block being presented with all three types of nest in turn and in a different order. If a nest was to be retained and presented to the same bird on a following day the box in which it had been built was carefully lifted without disturbing the nest and stored for later use. All groups of three tests were preceded by one dummy test, during which the bird was not observed, in order to
Animal Behaviour.
212
37, 2
Table 1. Prelaying behaviour of hens presented with three different types of nest: nest entries (~number of events &-SE), overall time from first entry to oviposition and its various components (min: RUSE)
A (flat Nest entries Overall time from nest entry Sitting Standing Gathering Rotating Litter placing Egg rolling Preening Pairwise
* Wilcoxon Friedman
B (preformed
8.413.6
1.1
0.6kO.3
7 22 I5 17 8.5
P (A versus NS
NS NS
< 0.02
tests were carried out on all A versus test indicated a statistically significant
provide a preformed nest should the sequence of three begin with a B or a C condition. A period of at least 24 h elapsed between the dummy test and the subsequent actual test. All analysis of behaviour was carried out by the same person and was limited to behaviour observed on the nest. The time which elapsed between first entry to the nest and oviposition was recorded, together with the number of nest entries. The categories of behaviour observed on the nest comprised: standing, sitting, rotating, gathering, litter placing, egg rolling and other (crouching, preening, scraping, sleeping). The activities of standing, sitting, crouching, preening and sleeping are self-explanatory. Rotating consisted of the hen sitting or crouching on the nest, rotating and scraping her feet out sideways. During these movements the keel was thrust down into the substrate and the rear part of the body was raised. Gathering consisted of any movements of the head and beak which resulted in litter being brought nearer to the hen’s body, and comprised three patterns described by Duncan & Kite (1989) namely ‘pecking’, ‘litterraking’ and ‘litter-gathering to the breast’. Litter-
P
3.3kO.5
43.7f7.l 21.346.1 2.710.5 6.7+ I.6 98+ I.9 2.3 10.7 0+X*0.4
0.7kO.3
nest entry
C (preformed nest) plus egg)
nest)
4.1+
33.1 *TV1 10.8k2.5 2.9kO.9 6.2k2.4 Il6+2.6
tests*
Overall time from Sitting Gathering Litter-placing
nest)
NS
81~0fll.9 47.4 f 9.9 3.7& I.3 8.9+ I.3 8,7+ I.8 3.7+ 1.3 5,5+ 1.4 2.3* 1.8 B)
T 1 35 14 I8
B. B versus effect.
P (B versus 10.01 NS
<0.5 NS C and A versus
co.01 io.01 NS
< 0.02 NS
i 0.02 NS
C)
T
P (A versus
I 0 15.5
to.01
6.5
10.01
C comparisons
C)
NS
where
the
placing involved the hen picking up litter in her beak and, in a rather slow deliberate movement, turning the head and neck towards the back of her body and dropping the material over her shoulder where it would fall on to her back or on to the side of the nest. Scraping involved sideways movements of the feet with no rotational movement of the body. The results were examined for statistical significance using the Friedman two-way analysis of variance for overall effects and the Wilcoxon matched pairs test for paired comparisons. These are appropriate tests where data are related and are not normally distributed. RESULTS
The various component behaviour patterns are given in Table I, which shows significant differences between treatments for overall time from first entry to oviposition, sitting, gathering and litterplacing. Total time from first entry to oviposition (Fig. 1) progressively increased from treatment A to treatment C, while the coefficient of variation
Hughes et al.: Nest building b)l 200. C . 180.
160.
140. 120;f‘ 5 E
. . IOO-
6
F 80.
.
. . .
.
.
A .
60.
40. . 20. 0
.
. m Nest type A
. . . Nest type B
J Nest type C
Figure 1. Scatter diagram of time from initial nest entry to oviposition. Individual values (0) with means and SE (0) for the three types of nest are given.
remained almost constant. The differences between C and A, and between C and B were significant, but not that between A and B. Sitting was significantly different in the three types, contributing 33% of the total time on the nest in A, 49% in B and 59% in C. Of the three litter-manipulating behaviour patterns, rotating showed no significant effect of treatment, while gathering and litter-placing both increased significantly in the preformed nests. When paired comparisons were tested, litter-placing was performed significantly more in B than in A, and in C than in A. Gathering occurred significantly more often in C than in B. Birds spent significantly more time sitting in C than in A. Egg rolling was a relatively important activity in C but could not, of course, occur in A or B. Scraping and sleeping occurred so rarely they are not shown. DISCUSSION There was a significant
difference
between treat-
domestie
hens
213
ments in the duration of pre-laying behaviour which, in the circumstances of this experiment, can be regarded as synonymous with time from first entry to oviposition; it was longest when birds were given a nest containing an egg and shortest when only the flat litter surface was presented. This longer duration of pre-laying behaviour could have been due to its earlier onset or to delayed laying. Although we think that the latter is unlikely, nevertheless it should be investigated in future studies. This increase in duration was apparently attributable both to the existence of a preformed nest (B) on which the hens spent 32% longer and also to the presence of an egg (C), for the hens spent 145% longer on a nest with an egg present than on the flat litter surface (A). It has long been known that nests with eggs are more attractive to domestic hens than nests without and that they are more likely to lay in nests with eggs than in other possible nest sites. This fact has been used to encourage laying in nests in practical husbandry systems but, as far as we are aware, this is the first report to demonstrate that hens spend longer on such nests before laying their egg. However, the hypothesis under investigation is that the form of the nest influences nest-building behaviour and, in order to test this, pre-laying behaviour must be partitioned into its various components. The number of nest entries did not differ between the three groups, in spite of its apparent preponderance in group A. Sitting behaviour was greater in B than in A and greater still in C. Two elements of nest building, gathering and litter-placing, lasted longer in B and longer still in C. Such findings are counterintuitive; it is difficult to explain why nest building should be more marked when the nest is already preformed. These findings appear to be contrary to Baxter’s (1983) hypothesis in that they suggest that, at least for domestic fowls, nest-building behaviour is motivated by factors other than the functional consequences of that behaviour. There was some evidence of feedback effects: rotating lasted longer on the flat litter surface, though the difference was not significant, and the duration of the other elements of nest building was greater on the preformed nests. What is especially dramatic is the evidence that, overall, performance of the behaviour was not inhibited by the existence of a nest which had already been provided by each bird for egg laying; such a finding must lead us to reject the hypothesis
214
Animal
Behazjiour,
that the proximate function of pre-laying behaviour is to construct a nest suitable for egg laying. The evidence from this study suggests that the performance of nest-building behaviour, regardless of its consequences, is reinforcing and is thus important to the fowl. The findings are consistent with Herrnstein’s (1977) proposition that ‘behaviour is itself a potent source of reinforcing stimuli, depending on the motivational state of the organism’. Supporting evidence that the performance of nest-building behaviour may in itself be reinforcing comes from Hinde’s (1958) study of canaries, Serinus canarius. When he deprived nesting canaries entirely of nest-building material, they developed habits which allowed at least some of the nesting behaviour to be shown and he concluded that the mere performance of nest-building behaviour has some reinforcing value even if no nest is built. In later experiments, Hinde & Steel (1972) found that elements of behaviour performed early in the sequence of canary nest building, such as pulling and gathering material, were maintained even when actual nest construction was prevented, suggesting that their performance may have been reinforcing. The present findings have important implications for the welfare of animals in intensive husbandry systems, both from a theoretical viewpoint, for they suggest that it may not be sufficient to provide animals with an environment which is adequate in its functional aspects (they may also require provision for the performance of behaviour), and also from the more practical standpoint of designing enclosures for laying hens. Although these findings suggest that the ability to perform behaviour is reinforcing in the context studied here, many questions remain unanswered. Is it also true of other behaviour and therefore a general rather than a specific conclusion? If needs are not met do animals suffer? If a need to perform pre-laying behaviour does exist, as this work suggests, could these needs be met by providing sufficient space and a suitable surface on which to stand? How motivated are hens to search out
37, 2
manipulable material? A start has already been made on answering these questions; it has been shown, for example, that hens prefer a nesting site with a substrate in which they can perform moulding with body and feet movements to one with loose material which they can manipulate with their beaks (Duncan & Kite 1989). ACKNOWLEDGMENTS This study was supported by a Commission from the Ministry of Agriculture, Fisheries and Food. REFERENCES Appleby, M. C. & McRae. H. 1986. The individual nest box as a super-stimulus for domestic hens. App/. Anim. Behav. Sci., 15, 169-176. Baxter, M. 1983. Ethology in environmental design for animal production. Appl. Anim. Ethel., 9, 207-220. Command Paper 2836. 1965. Report of the Technical Committee IO Enquire into the Werare of’Animals kept under Intensive Livestock Husbandry Systems. London:
Her Majesty’s Stationery Office. Dawkins, M. S. 1983. Battery hens name their price: consumer demand theory and the measurement of ethological ‘needs’. Anim. Behav.. 31, 1195-1205. Duncan, I. J. H. 1987. The welfare of farm animals: an ethological approach. Sci. Prog., OxJ, 71, 319-328. Duncan, I. J. H. & Kite, V. G. 1989. Nest-site selection and nest-building behaviour in domestic fowl. Anim. Behav, 37,215-23 1. Hermstein, R. J. 1977. The evolution of behaviorism. Am. Psychol.,
32, 593-603.
Hinde, R. A. 1958. The nest-building behaviour of domesticated canaries. Proc. zoo/. Sot. Lond., 131, I48. Hinde, R. A. & Steel, E. 1972. Reinforcing events in the integration of canary nest-building. Anim. Behav., 20, 5 14-525. Hughes, B. 0. & Duncan, I. J. H. 1988. The notion of ethological ‘need’, models of motivation and animal welfare. Anim. Behav., 36, 1696-1707. Wood-Gush, D. G. M. 1975. Nest construction by the domestic hen: some comparative and physiological considerations. Neural and Endocrine Aspects of Behaviour in Birds (Ed. by P. Wright, P. G. Caryl & D. M. Vowles), pp. 35-49. Oxford: Elsevier. (Received
16 December MS.
1987; revised 18 February number: 3131)
1988,
The performance of nest building by domestic hens: is it more important than the construction of a nest? B. 0. HUGHES, I. J. H. DUNCAN & MARGRETTA AFRC Institute of Animal Physiology and Genetics Research, Edinburgh Midlothian EH25 9PS, U.K.
F. BROWN Research Station, Roslin,
Abstract. Domestic hens were presented with three different types of littered nest: a flat litter surface (A), a preformed hollowed nest (B) and a preformed nest with an egg (C). Nests B and C had been previously constructed by the hen under test. The overall duration of pre-laying behaviour was greater in nest type C than in both nest types A and B. Of the three nest-building behaviour patterns, gathering, in which the hen moved litter nearer to her body with head and beak movements, and litter-placing, in which she picked up particles of litter and dropped them over her shoulder, increased in the preformed nests compared with the control. Rotating, in which the hen crouched on the nest, rotated and scraped outwards with her feet, did not differ between treatments. Thus, nest-building behaviour was not inhibited by the existence of a preformed nest. This finding does not support the hypothesis that animal welfare in intensive housing can be safeguarded merely by providing that environment which would have been created by the animal’s own activities. Rather, it suggests that performance of behaviour can in itself be reinforcing and that provision is required for such behaviour to be carried out. This finding may also have important implications for general motivational theory.
The concept of behavioural ‘need’ (the notion that animals’ welfare may suffer if they are unable to carry out particular behaviour patterns) was first set out in the report of the Brambell Committee (Command Paper 2836 1965) very much under the influence of W. H. Thorpe. The concept has since received a good deal of attention and criticism from applied ethologists, who have generally regarded it as having merit and utility, but requiring to be placed on a much more secure scientific footing (for example, see Dawkins 1983; Duncan 1987; Hughes & Duncan 1988). It has been enshrined in the European Convention on Animal Welfare and is one of the U.K. Farm Animal Welfare Committee’s objectives as providing animals in intensive husbandry systems with the ‘freedom to perform most normal patterns of behaviour’. The concept that the performance of behaviour, per se, may be important to animals has been questioned by Baxter (1983). He has postulated that behaviour, in this context, serves two main functions. (1) It contributes to biological fitness and, in domestic animals, to productivity. (2) It returns, through its functional consequences, the animal’s control system to a homeostatic set point and thereby switches off motivation. For welfare to be achieved, behavioural control 0003-3472,'89/020210+05$03.00/0
systems should remain at, or be allowed to return to, their set points. However, welfare is often at risk in intensive conditions because animals have not evolved in these environments and there is therefore a mismatch between the control system and the environment. Baxter (1983) gives appetite as a possible example. Many animals housed over long periods in intensive environments with access to food ad libitum become obese; this may be because the animals have not adjusted to the lower maintenance requirements so the set point for satiety is now at an inappropriately high level. Baxter (1983) then goes on to argue that, in relation to point (2) above, animal welfare in intensive environments may be safeguarded just as effectively by providing animals with the functional consequences resulting from the behaviour which they would have performed, rather than allowing them actually to perform the behaviour. He cites, as an example, nest building in sows, Sus scroja. The nest serves a number of functions, providing insulation, warmth, softness and protection for the piglets and support and cushioning for the udder of the sow. If all these functions could be provided by an artificial nest for sows then, Baxter argues, the sow would not be motivated to build a nest and the behaviour would not occur. One of the problems with Baxter’s hypothesis is
X‘ 1989 The Association for the Study 210
of
Animal Behaviour
Huglws et al.: Nest building !I!> domestic hens that it is difficult to disprove. Even if an artificial nest, believed to meet all the functions specified for the natural nest, was constructed but the sow continued to display nest-building behaviour, one could not state with certainty that the hypothesis had been disproved. It might be that the natural nest served other functions, as yet unidentified. which were not met by the artificial nest. However, the domestic fowl, Gullus gal/us domesticus, provides a particularly suitable model to examine this question. The hen, housed under semi-intensive conditions, with access to an approcomplex priate substrate, shows a relatively sequence of pre-laying behaviour and builds a new nest each time she lays an egg. This nest, though generally rudimentary, is built in a similar location time after time, often using the same materials (Wood-Gush 1975). Because many hens lay a long series of eggs on successive days it is easy to collect data, in contrast to sows, which farrow only two or three times per annum. In particular, the nest built by the hen herself on one day can be presented to her again on the following day, when it should more fully meet her requirements than it did originally. The experiment described in this paper was designed to test the hypothesis that the proximate function of nest-building behaviour is to construct a nest suitable for egg laying. The null hypothesis was that hens would display a similar pattern of nest building and pre-laying behaviour, regardless of whether they were presented with a featureless area of litter or with a preformed nest. Because it is not certain what a hen would regard as a preconstructed nest site, they were offered on separate occasions both a preformed empty nest and a preformed nest containing one egg.
MATERIALS
AND
METHODS
The 12 hens were 40-week-old ISA Browns (medium hybrid brown egg layers) which had all previously taken part in an experiment on nest-site selection and had subsequently been housed for some weeks in single battery cages, so were experienced in laying in a number of different types of nest site. About a week before each bird was tested she was placed with two others in a pen (2.4 x 2.4 m) with a littered floor, food hopper, drinking trough and littered open nestbox in order to accustom her to the type of environment in which
211
she would be tested. Most hens laid in the nestbox provided; any that did not were picked up while displaying pre-laying behaviour and placed gently in the box so that they became used to laying there. The test-pen was next to the home-pen and was of similar dimensions. It had a painted concrete floor and a nest site in the corresponding corner to that occupied by the nestbox in the home-pen. The nest site was an open wooden box (0.39 x 0.39 m with sides 0.10 m high) filled with wood shavings similar to those in the nestbox in the home pen. This site met the criteria set out by Appleby & McRae (1986) for a minimal nest site. A video camera was mounted in another corner of the pen and all behaviour displayed on the nest site was recorded for later analysis. The test-pen into which the hen was placed contained the nest site in one of three states which comprised the three treatments. In treatment A the box contained wood shavings levelled out to form a relatively flat surface about 6 cm below the top of the sides. In treatment B the box contained a nest previously constructed by that particular hen on an earlier occasion, often, but not always, on the previous day. The nest typically took the form of a hollow with a raised rim consisting of a mixture of wood shavings and feathers. In treatment C the box contained a nest previously constructed by that hen together with the egg she had laid in it (C). The presentation of nests took the form of a 3 x 3 Latin Square design with three hens being presented with all three types of nest in turn and in a different order. Only one nest of one type was presented to a hen on any one day. On occasion, the test ended sufficiently early for a second hen to be tested later on the same day. The hen’s laying record in her home-pen was monitored and on a test day she was placed in the pen at least 2 h before her expected time of lay, though sometimes the elapsed time before oviposition proved to be much longer. This period had to be considerable in order to avoid the possibility that she had already begun to display pre-laying behaviour in the home-pen. The experiment was carried out in four blocks, with each of the three hens in each block being presented with all three types of nest in turn and in a different order. If a nest was to be retained and presented to the same bird on a following day the box in which it had been built was carefully lifted without disturbing the nest and stored for later use. All groups of three tests were preceded by one dummy test, during which the bird was not observed, in order to
Animal Behaviour.
212
37, 2
Table 1. Prelaying behaviour of hens presented with three different types of nest: nest entries (~number of events &-SE), overall time from first entry to oviposition and its various components (min: RUSE)
A (flat Nest entries Overall time from nest entry Sitting Standing Gathering Rotating Litter placing Egg rolling Preening Pairwise
* Wilcoxon Friedman
B (preformed
8.413.6
1.1
0.6kO.3
7 22 I5 17 8.5
P (A versus NS
NS NS
< 0.02
tests were carried out on all A versus test indicated a statistically significant
provide a preformed nest should the sequence of three begin with a B or a C condition. A period of at least 24 h elapsed between the dummy test and the subsequent actual test. All analysis of behaviour was carried out by the same person and was limited to behaviour observed on the nest. The time which elapsed between first entry to the nest and oviposition was recorded, together with the number of nest entries. The categories of behaviour observed on the nest comprised: standing, sitting, rotating, gathering, litter placing, egg rolling and other (crouching, preening, scraping, sleeping). The activities of standing, sitting, crouching, preening and sleeping are self-explanatory. Rotating consisted of the hen sitting or crouching on the nest, rotating and scraping her feet out sideways. During these movements the keel was thrust down into the substrate and the rear part of the body was raised. Gathering consisted of any movements of the head and beak which resulted in litter being brought nearer to the hen’s body, and comprised three patterns described by Duncan & Kite (1989) namely ‘pecking’, ‘litterraking’ and ‘litter-gathering to the breast’. Litter-
P
3.3kO.5
43.7f7.l 21.346.1 2.710.5 6.7+ I.6 98+ I.9 2.3 10.7 0+X*0.4
0.7kO.3
nest entry
C (preformed nest) plus egg)
nest)
4.1+
33.1 *TV1 10.8k2.5 2.9kO.9 6.2k2.4 Il6+2.6
tests*
Overall time from Sitting Gathering Litter-placing
nest)
NS
81~0fll.9 47.4 f 9.9 3.7& I.3 8.9+ I.3 8,7+ I.8 3.7+ 1.3 5,5+ 1.4 2.3* 1.8 B)
T 1 35 14 I8
B. B versus effect.
P (B versus 10.01 NS
<0.5 NS C and A versus
co.01 io.01 NS
< 0.02 NS
i 0.02 NS
C)
T
P (A versus
I 0 15.5
to.01
6.5
10.01
C comparisons
C)
NS
where
the
placing involved the hen picking up litter in her beak and, in a rather slow deliberate movement, turning the head and neck towards the back of her body and dropping the material over her shoulder where it would fall on to her back or on to the side of the nest. Scraping involved sideways movements of the feet with no rotational movement of the body. The results were examined for statistical significance using the Friedman two-way analysis of variance for overall effects and the Wilcoxon matched pairs test for paired comparisons. These are appropriate tests where data are related and are not normally distributed. RESULTS
The various component behaviour patterns are given in Table I, which shows significant differences between treatments for overall time from first entry to oviposition, sitting, gathering and litterplacing. Total time from first entry to oviposition (Fig. 1) progressively increased from treatment A to treatment C, while the coefficient of variation
Hughes et al.: Nest building b)l 200. C . 180.
160.
140. 120;f‘ 5 E
. . IOO-
6
F 80.
.
. . .
.
.
A .
60.
40. . 20. 0
.
. m Nest type A
. . . Nest type B
J Nest type C
Figure 1. Scatter diagram of time from initial nest entry to oviposition. Individual values (0) with means and SE (0) for the three types of nest are given.
remained almost constant. The differences between C and A, and between C and B were significant, but not that between A and B. Sitting was significantly different in the three types, contributing 33% of the total time on the nest in A, 49% in B and 59% in C. Of the three litter-manipulating behaviour patterns, rotating showed no significant effect of treatment, while gathering and litter-placing both increased significantly in the preformed nests. When paired comparisons were tested, litter-placing was performed significantly more in B than in A, and in C than in A. Gathering occurred significantly more often in C than in B. Birds spent significantly more time sitting in C than in A. Egg rolling was a relatively important activity in C but could not, of course, occur in A or B. Scraping and sleeping occurred so rarely they are not shown. DISCUSSION There was a significant
difference
between treat-
domestie
hens
213
ments in the duration of pre-laying behaviour which, in the circumstances of this experiment, can be regarded as synonymous with time from first entry to oviposition; it was longest when birds were given a nest containing an egg and shortest when only the flat litter surface was presented. This longer duration of pre-laying behaviour could have been due to its earlier onset or to delayed laying. Although we think that the latter is unlikely, nevertheless it should be investigated in future studies. This increase in duration was apparently attributable both to the existence of a preformed nest (B) on which the hens spent 32% longer and also to the presence of an egg (C), for the hens spent 145% longer on a nest with an egg present than on the flat litter surface (A). It has long been known that nests with eggs are more attractive to domestic hens than nests without and that they are more likely to lay in nests with eggs than in other possible nest sites. This fact has been used to encourage laying in nests in practical husbandry systems but, as far as we are aware, this is the first report to demonstrate that hens spend longer on such nests before laying their egg. However, the hypothesis under investigation is that the form of the nest influences nest-building behaviour and, in order to test this, pre-laying behaviour must be partitioned into its various components. The number of nest entries did not differ between the three groups, in spite of its apparent preponderance in group A. Sitting behaviour was greater in B than in A and greater still in C. Two elements of nest building, gathering and litter-placing, lasted longer in B and longer still in C. Such findings are counterintuitive; it is difficult to explain why nest building should be more marked when the nest is already preformed. These findings appear to be contrary to Baxter’s (1983) hypothesis in that they suggest that, at least for domestic fowls, nest-building behaviour is motivated by factors other than the functional consequences of that behaviour. There was some evidence of feedback effects: rotating lasted longer on the flat litter surface, though the difference was not significant, and the duration of the other elements of nest building was greater on the preformed nests. What is especially dramatic is the evidence that, overall, performance of the behaviour was not inhibited by the existence of a nest which had already been provided by each bird for egg laying; such a finding must lead us to reject the hypothesis
214
Animal
Behazjiour,
that the proximate function of pre-laying behaviour is to construct a nest suitable for egg laying. The evidence from this study suggests that the performance of nest-building behaviour, regardless of its consequences, is reinforcing and is thus important to the fowl. The findings are consistent with Herrnstein’s (1977) proposition that ‘behaviour is itself a potent source of reinforcing stimuli, depending on the motivational state of the organism’. Supporting evidence that the performance of nest-building behaviour may in itself be reinforcing comes from Hinde’s (1958) study of canaries, Serinus canarius. When he deprived nesting canaries entirely of nest-building material, they developed habits which allowed at least some of the nesting behaviour to be shown and he concluded that the mere performance of nest-building behaviour has some reinforcing value even if no nest is built. In later experiments, Hinde & Steel (1972) found that elements of behaviour performed early in the sequence of canary nest building, such as pulling and gathering material, were maintained even when actual nest construction was prevented, suggesting that their performance may have been reinforcing. The present findings have important implications for the welfare of animals in intensive husbandry systems, both from a theoretical viewpoint, for they suggest that it may not be sufficient to provide animals with an environment which is adequate in its functional aspects (they may also require provision for the performance of behaviour), and also from the more practical standpoint of designing enclosures for laying hens. Although these findings suggest that the ability to perform behaviour is reinforcing in the context studied here, many questions remain unanswered. Is it also true of other behaviour and therefore a general rather than a specific conclusion? If needs are not met do animals suffer? If a need to perform pre-laying behaviour does exist, as this work suggests, could these needs be met by providing sufficient space and a suitable surface on which to stand? How motivated are hens to search out
37, 2
manipulable material? A start has already been made on answering these questions; it has been shown, for example, that hens prefer a nesting site with a substrate in which they can perform moulding with body and feet movements to one with loose material which they can manipulate with their beaks (Duncan & Kite 1989). ACKNOWLEDGMENTS This study was supported by a Commission from the Ministry of Agriculture, Fisheries and Food. REFERENCES Appleby, M. C. & McRae. H. 1986. The individual nest box as a super-stimulus for domestic hens. App/. Anim. Behav. Sci., 15, 169-176. Baxter, M. 1983. Ethology in environmental design for animal production. Appl. Anim. Ethel., 9, 207-220. Command Paper 2836. 1965. Report of the Technical Committee IO Enquire into the Werare of’Animals kept under Intensive Livestock Husbandry Systems. London:
Her Majesty’s Stationery Office. Dawkins, M. S. 1983. Battery hens name their price: consumer demand theory and the measurement of ethological ‘needs’. Anim. Behav.. 31, 1195-1205. Duncan, I. J. H. 1987. The welfare of farm animals: an ethological approach. Sci. Prog., OxJ, 71, 319-328. Duncan, I. J. H. & Kite, V. G. 1989. Nest-site selection and nest-building behaviour in domestic fowl. Anim. Behav, 37,215-23 1. Hermstein, R. J. 1977. The evolution of behaviorism. Am. Psychol.,
32, 593-603.
Hinde, R. A. 1958. The nest-building behaviour of domesticated canaries. Proc. zoo/. Sot. Lond., 131, I48. Hinde, R. A. & Steel, E. 1972. Reinforcing events in the integration of canary nest-building. Anim. Behav., 20, 5 14-525. Hughes, B. 0. & Duncan, I. J. H. 1988. The notion of ethological ‘need’, models of motivation and animal welfare. Anim. Behav., 36, 1696-1707. Wood-Gush, D. G. M. 1975. Nest construction by the domestic hen: some comparative and physiological considerations. Neural and Endocrine Aspects of Behaviour in Birds (Ed. by P. Wright, P. G. Caryl & D. M. Vowles), pp. 35-49. Oxford: Elsevier. (Received
16 December MS.
1987; revised 18 February number: 3131)
1988,