Rate Of Pecking Research Articles

Behavioral, physiological, and endocrine responses of starlings to acute increases in density

One potential stressor to vertebrates both in the wild and in captivity is the presence of numerous individuals in a confined space. To examine the effects of increased conspecific density in birds, we simultaneously measured cardiac, behavioral, and endocrine responses of European starlings ( Sturnus vulgaris) to acute crowding. A cage containing a resident bird was outfitted with a trap door that allowed for the introduction of intruder birds (one, three, or five birds) without human interference. The resident bird was implanted with a subcutaneous heart rate (HR) transmitter, behavior was videotaped through a two-way mirror, and blood samples were taken at the end of each treatment to determine plasma corticosterone (CORT) concentrations. Resident starlings significantly increased both general activity and aggressive behaviors while decreasing preening following the initiation of elevated conspecific density. Intruder starlings increased feeding, drinking, and aggressive pecking rates, but postintrusion feeding rates decreased as intruder number increased. Preening decreased in both residents and intruders following the intrusion. HR increased in the resident starlings at the time of intruder introduction, with an increase in the magnitude of this response directly correlating with increasing intruder number. The CORT response to increased density was dependent on social role (resident or intruder), since increasing density did not alter CORT levels in resident birds, but resulted in elevated CORT 30 min following the five-intruder introduction in the intruder birds. Together, these data suggest that increased conspecific density is a significant acute stressor in starlings which is capable of inducing aggression in both residents and intruders. Furthermore, it elicits different responses from different physiological and behavioral systems, and behavioral responses such as feeding and general activity may be density-dependent. The data specifically illustrate that cardiac and behavioral activation can be independent of CORT release, and the CORT response of starlings to increased conspecific density is dependent on social role and degree of the increase in density.

Elemental versus configural perception in a people-present/people-absent discrimination task by pigeons.

In the present experiment, we investigated whether pigeons rely exclusively on elemental information or whether they are also able to exploit configural information in a people-present/people-absent discrimination task. Six pigeons were trained in a go/no-go procedure to discriminate between 800 color photographs characterized by the presence or absence of people. The people-present stimuli were designated as positive, and the people-absent stimuli were designated as negative. After training and a subsequent generalization test, the pigeons were presented with both familiar and novel people-present stimuli containing human figures that were distorted in one of seven different ways. All the pigeons learned the initial discrimination and also showed generalization to novel stimuli. In the subsequent test, performance on all types of distorted stimuli was diminished in comparison with that on the intact original pictures from which they had been derived. At the same time, however, peck rates clearly exceeded the level of responding found for regular people-absent stimuli. This result strongly suggests that responding was controlled by both the constituting target components and their spatial relations and, therefore, points to the dual importance of elemental and configural information.

Economic and biological influences on key pecking and treadle pressing in pigeons.

Pigeons were studied on a two-component multiple schedule in which the required operant was, in different conditions, biologically relevant (i.e., key pecking) or nonbiologically relevant (i.e., treadle pressing). Responding was reinforced on a variable-interval (VI) 2-min schedule in both components. In separate phases, additional food was delivered on a variable-time (VT) 15-s schedule (response independent) or a VI 15-s schedule (response dependent) in one of the components. The addition of response-independent food had different effects on responding depending on the operant response and on the frequency with which the components alternated. When components alternated frequently (every 10 s), all pigeons keypecked at a much higher rate during the component with the additional food deliveries, whether response dependent or independent. In comparison, treadle pressing was elevated only when the additional food was response dependent; rate of treadling was lower when the additional food was response independent. When components alternated infrequently (every 20 min), pigeons key pecked at high rates at points of transition into the component with the additional food deliveries. Rate of key pecking decreased with time spent in the 20-min component when the additional food was response independent, whereas rate of pecking remained elevated in that component when the additional food was response dependent. Under otherwise identical test conditions, rate of treadle pressing varied only as a function of its relative rate of response-dependent reinforcement. Delivery of response-independent food thus had different, but predictable, effects on responding depending on which operant was being studied, suggesting that animal-learning procedures can be integrated with biological considerations without the need to propose constraints that limit general laws of learning.

Good foragers can also be good at detecting predators.

The degree to which foraging and vigilance are mutually exclusive is crucial to understanding the management of the predation and starvation risk trade-off in animals. We tested whether wild-caught captive chaffinches that feed at a higher rate do so at the expense of their speed in responding to a model sparrowhawk flying nearby, and whether consistently good foragers will therefore tend to respond more slowly on average. First, we confirmed that the time taken to respond to the approaching predator depended on the rate of scanning: as head-up rate increased so chaffinches responded more quickly. However, against predictions, as peck rate increased so head-up rate increased and mean length of head-up and head-down periods decreased. Head-up rate was probably dependent on peck rate because almost every time a seed was found, a bird raised its head to handle it. Therefore chaffinches with higher peck rates responded more quickly. Individual chaffinches showed consistent durations of both their head-down and head-up periods and, therefore, individuals that were good foragers were also good detectors of predators. In relation to the broad range of species that have a similar foraging mode to chaffinches, our results have two major implications for predation/starvation risk trade-offs: (i) feeding rate can determine vigilance scanning patterns; and (ii) the best foragers can also be the best at detecting predators. We discuss how our results can be explained in mechanistic terms relating to fundamental differences in how the probabilities of detecting food rather than a predator are affected by time. In addition, our results offer a plausible explanation for the widely observed effect that vigilance continues to decline with group size even when there is no further benefit to reducing vigilance.

The functional response in three species of herbivorous Anatidae: effects of sward height, body mass and bill size

Summary The functional response, i.e. the quantity of food consumed per unit of time as a function of food availability, is a central process in foraging ecology. The application of this concept to foraging by mammalian herbivores has led to major insights into the process of resource acquisition, but it has so far been little used to understand foraging in avian herbivores. In this study, we describe the functional responses of three grazing Anatidae, the wigeon Anas penelope L. (mean body mass in this study 620 g), the barnacle goose Branta leucopsis B. (2000 g), and the greylag goose Anser anser L. (3500 g). We measured instantaneous intake rates on eight grass heights from 1 cm to 12 cm, as well as pecking rates and peck sizes, and used the Spalinger–Hobbs model developed for mammalian herbivores to explore the mechanisms limiting intake in these three species. Greylag geese increased their intake rate with increasing food availability (a Type II response), wigeon showed a weak quadratic (Type IV) response, and intake rate by barnacle geese did not vary significantly across the range of variability we offered the birds. Intake rates differed markedly between individuals, especially in greylag geese, where body mass explained much of the variation. For individuals in all three species, peck sizes strongly influenced instantaneous intake rates, and the size of the bill (width in particular) appeared to be an important determinant of peck size. Peck sizes increased with sward height (although only very weakly in wigeon), but so did cropping time for wigeon and barnacle geese, which led to a significant decline of intake rates on the tallest grass, at least in the small wigeon. For these very selective small herbivores, the time to crop a mouthful was therefore a significant limiting factor for the birds’ instantaneous intake rate (in addition to peck size and swallowing time). This differs markedly from the situation in mammalian herbivores where bite size (through chewing time) is the principal controlling process in food concentrated patches, a result that we found in greylag geese. We discuss the differences in foraging between the three species in relation to their principal food resources, body mass and bill morphology.

Operant discriminative learning and evidence of subtelencephalic plastic changes after long-term detelencephalation in pigeons.

We analyzed operant discrimination in detelencephalated pigeons and neuroanatomical substrates after long-term detelencephalation. In Experiment I, experimental pigeons with massive telencephalic ablation and control pigeons were conditioned to key peck for food. Successive discrimination was made under alternating red (variable-ratio reinforcement) and yellow (extinction) lights in one key of the chamber. These relations were interchanged during reversal discrimination. The sessions were run until steady-state rates were achieved. Experiment II analyzed the morphology of the nucleus rotundus and optic tectum in long-term detelencephalated and control birds, using a Klüver-Barrera staining and image analyzer system. Detelencephalated birds had more training sessions for response shaping and steady-state behavior (p<0.001), higher red key peck rates during discrimination (p<0.01), and reversal discrimination indexes around 0.50. Morphometric analysis revealed a decreased number of neurons and increased vascularity, associated with increases in the perimeter (p<0.001) in the nucleus rotundus. In the optic tectum, increases in the perimeter (p<0.05) associated with disorganization in the layers arrangement were seen. The data indicate that telencephalic systems might have an essential function in reversal operant discrimination learning. The structural characteristics of subtelencephalic systems after long-term detelencephalation evidence plastic changes that might be related to functional mechanisms of learning and neural plasticity in pigeons.

Effects of D-amphetamine in a temporal discrimination procedure: selective changes in timing or rate dependency?

Two experiments evaluated rate dependency and a neuropharmacological model of timing as explanations of the effects of amphetamine on behavior under discriminative control by time. Four pigeons pecked keys during 60-trial sessions. On each trial, the houselight was lit for a particular duration (5 to 30 s), and then the key was lit for 30 s. In Experiment 1, the key could be lit either green or blue. If the key was lit green and the sample was 30 s, or if the key was lit blue and the sample was 5 s, pecks produced food on a variable-interval 20-s schedule. The rate of key pecking increased as a function of sample duration when the key was green and decreased as a function of sample duration when the key was blue. Acute d-amphetamine (0.1 to 3.0 mg/kg) decreased higher rates of key pecking and increased lower rates of key pecking as predicted by rate dependency, but did not shift the timing functions leftward (toward overestimation) as predicted by the neuropharmacological model. These results were replicated in Experiment 2, in which the key was lit only one color during sessions, indicating that the effects were not likely due to disruption of discriminative control by key color. These results are thus consistent with rate dependency but not with the predictions of the neuropharmacological model.

Habitat selection and conservation of Sharpe's longclaw (Macronyx sharpei), a threatened Kenyan grassland endemic

Montane grassland is a severely threatened habitat in Kenya. Despite a high level of faunal endemism, it has received very little conservation attention. We investigated habitat selection in a threatened grassland endemic bird species, Sharpe's longclaw (Macronyx sharpei) (family Motacillidae), in order to understand its likely response to land-use changes. Between November 1995 and May 1996, we studied 41 territories of this species on the Kinangop Plateau in central Kenya. With an overall density of 0.4 birds ha−1, longclaws lived in permanent groups of two to seven individuals. They were sedentary and territorial, with a mean home range size of 0.5 ha. The species avoided non-grassland areas entirely, and within grassland showed a strong preference for short grass with tussocks. Territory sizes and foraging ranges were smaller, and rates of pecking for food higher, in this grassland type than in open short grass or long grass. Land use changes, in particular conversion to cultivation or woodlots and ploughing up of grassland to remove tussocks, pose a serious and immediate threat to this species. Dairy farming is potentially compatible with grassland conservation, and conservation-friendly livestock rearing needs to be promoted through economic incentives, awareness-raising and technical advice.

Timing and Foraging: Gibbon's Scalar Expectancy Theory and Optimal Patch Exploitation

We present a study that links optimal foraging theory (OFT) to behavioral timing. OFT's distinguishing feature is the use of models that compute the most advantageous behavior for a particular foraging problem and compare the optimal solution to empirical data with little reference to psychological processes. The study of behavioral timing, in contrast, emphasizes performance in relation to time, most often without strategic or functional considerations. In three experiments, reinforcer-maximizing behavior and timing performance are identified and related to each other. In all three experiments starlings work in a setting that simulates food patches separated by a flying distance between the two perches. The patches contain a variable and unpredictable number of reinforcers and deplete suddenly without signal. Before depletion, patches deliver food at fixed intervals (FI). Our main dependent variables are the times of occurrence of three behaviors: the “peak” in pecking rate (Peak), the time of the last peck before “giving in” (GIT), and the time for “moving on” to a new patch (MOT). We manipulate travel requirement (Experiment 1), level of deprivation and FI (Experiment 2), and size of reinforcers (Experiment 3). For OFT, Peak should equal the FI in all conditions while GIT and MOT should just exceed it. Behavioral timing and Scalar Expectancy Theory (SET) in particular predict a Peak at around the FI and a longer (unspecified) GIT, and make no prediction for MOT. We found that Peak was close to the FI and GIT was approximately 1.5 times longer, neither being affected by travel, hunger, or reinforcer size manipulations. MOT varied between 1.5 and just over 3 times the FI, was responsive to both travel time and the FI, and did not change when the reinforcer rate was manipulated. These results support the practice of producing models that explicitly separate information available to the subject from strategic use of this information.

Pecking preferences in hatchlings of the Australian brush-turkey, Alectura lathami (Megapodiidae): the role of food type and colour

Chicks of megapodes, including the Australian brush-turkey, Alectura lathami, live independently, without parents to show them where and what to eat. This paper represents the first investigation of how megapode chicks find and identify food. The specific questions addressed are: whether naive brush-turkey hatchlings are able to differentiate between food and objects that do not give a nutritional reward; whether they possess a preference for certain types of food; and which factors are most likely to trigger feeding in hatchlings. The three questions were approached by pairwise choice tests of two types. In Type 1, chicks were offered mealworm larvae, fruit cubes, seeds and non-nutritious objects (pebbles); in Type 2, chicks were offered beads of four different colours (red, green, blue and yellow). The median peck rate at pebbles was always significantly lower than that at mealworms, fruit or seeds. Mealworms received significantly more pecks than seeds or pebbles. Chicks showed no clear preference for any colour. All chicks also directed some pecks at ‘other items’ that appeared to display a strong contrast against the background of the box they were kept in, either in colour (e.g. dark knotholes in light brown wood) or in shape (three-dimensional, such as claws and faeces). Hatchlings seem to direct their initial pecks at objects that have certain characteristics in common, such as contrast, movement (for live prey) and reflective surfaces (for fruit or seeds). Preference for these rather general characteristics may be adaptive considering that chicks can hatch in various habitats and different months of the year, making the types of food available at hatching unpredictable.

Postfledging crèche behavior in the European shag

Formation of a postfledgling creche in the European shag Phalacrocorax aristotelis on the Cies Islands (northwest Spain) was studied. There was no relationship between the number of birds in a creche and environmental temperature. Moreover, the number of juveniles in the creche was not correlated with adult peck rate per juvenile. Also, predation was not reported on the studied population. Therefore, their postfledging creche did not serve as protection from thermal stress, aggressiveness of adults, or predators. In the creche studied, fledglings are faithful to their perch, which serves as a functional unit where they form a group consisting of stable members. I postulate that there may be advantages in the formation of creches, which allow adults to be able to locate their young and continue their postfledging parental care and also enable chicks to exercise and develop fishing skills. Adults remained in the creche during the entire period, but their number depended on the hour and tide, which would be associated with the effectiveness of fishing according to these factors. Moreover, creches may facilitate finding mates and forming feeding groups.

The social transmission of feather pecking in laying hens: effects of environment and age

Abnormal behaviours, such as feather pecking, can become an even greater problem if they spread through the flock. Domestic hens are a social species and it has been suggested that feather pecking behaviour can be socially transmitted from few feather pecking individuals to many. The purpose of this experiment was to investigate whether feather pecking is transmitted from an experimental strain of high feather peckers to an experimental strain of low feather peckers when housed together. The effects of environment and age were also investigated. Four hundred and twenty chicks were housed in either cages or pens in one of three treatment groups; all high feather peckers, all low feather peckers, and a mixed group of half high feather peckers and half low feather peckers. During the rearing phase, severe and gentle feather pecks were recorded at 13–15 weeks and feather plumage scored at 12 and 17 weeks. At 17 weeks of age, the groups of mixed hens were removed from the study and the remaining hens resorted into the same three treatment groups. During the laying phase, severe and gentle feather pecks were recorded at 30–32 weeks of age and feather plumage was scored at 29 weeks of age. There was significantly less feather pecking and plumage damage in the pens than in the cages. There was no evidence of severe feather pecking spreading from feather peckers to non-feather peckers, even when actual rates of feather pecking were examined rather than only considering the strain of hen. There was some evidence that gentle feather pecking was transmitted in laying hens housed in cages. However, as gentle feather pecking does not lead to plumage damage, this is less relevant to commercial practice.

Does the thermal environment influence vigilance behavior in dark-eyed juncos ( Junco hyemalis)? An approach using standard operative temperature

One might expect that increased thermal stress would cause wintering birds to forage faster in order to meet the increased metabolic demand. Faster foraging should, in turn, lead to a reduction in vigilance, since feeding and vigilance are mutually antagonistic activities. We examined these intuitive behavioral expectations using newly developed standard operative temperature sensors designed specifically to characterize the thermal effect of the microclimate environment (rain excluded) on wintering dark-eyed juncos ( Junco hyemalis). These sensors allowed us to distinguish the behavioral effects of thermal stress from non-thermal effects associated with micrometeorological conditions (e.g. wind noise). Our analysis indicated that neither thermal nor non-thermal aspects of the physical environment influenced the proportion of time spent vigilant by juncos. However, the rate of food ingestion (measured as pecking rate) exhibited a negative correlation with thermal stress per se. This unexpected result may reflect the effect of thermal stress on feeding posture, peripheral muscle cooling, or both. The effect of thermal stress on pecking rate was nevertheless minor in comparison to the effect of flock size, which exerted by far the largest effect on both vigilance and pecking rate. Our overall results suggest that birds experiencing thermal stress will not necessarily lower their vigilance, but rather increase feeding bout length to compensate for the greater metabolic demand. This interpretation is consistent with theoretical models of vigilance in a non-time-limited environment, and may help explain the contradictory results to date on the effect of thermal stress on vigilance.

How to hatch from an egg of great structural strength. A study of the Common Cuckoo

Brood parasitism represents a unique mode of avian reproduction that requires a number of adaptations. For example, to reduce chances of puncture ejection of their eggs by small hosts, brood parasites may have been selected for laying eggs of unusually great structural strength. However, great structural strength of eggshells should hinder hatching. The goals of our study were to establish if chicks of the Common Cuckoo Cuculus canorus have more difficulty with hatching out of their strong eggs than chicks of species with eggs of similar size, and whether they possess any mechanisms facilitating hatching. To achieve these goals, we compared hatching pattern and selected body characteristics of chicks of the Common Cuckoo with those of another altricial species with eggs of a similar size, the Great Reed Warbler Acrocephalus arundinaceus. Although the rate of pecking was similar in the two species, the Common Cuckoo chicks started pecking earlier in relation to their emergence and consequently required more time and a greater cumulative number of pecks for breaking open their eggs than did young Great Reed Warblers. The two species also differed with respect to the pattern of opening their shells; in contrast to the warbler chicks, which enlarged the original pip circularly, the cuckoo chicks opened the egg by systematically creating a long narrow slit until they emerged. Finally, our study of hatched young revealed several differences; the Cuckoo hatchlings were significantly heavier, had a longer forearm, and their egg tooth was located significantly farther from the tip of the beak. The edge used for cutting through the shell was also significantly longer than that of hatchling Great Reed Warblers. To conclude, our data suggest that hatching is more difficult for a Cuckoo than for a Great Reed Warbler and that Cuckoos possess several mechanisms to overcome the problems of hatching from a structurally strong egg.

Assessment of food intake rates in pink‐footed geese Anser brachyrhynchus based on examination of oesophagus contents

An alternative to the so‐called ‘marker substance’ method used to estimate daily food intake in geese is presented. Based on the assumption that a grazing bird takes one leaf per peck, the daily food intake rate can be calculated by multiplying mean bite weight, peck rate and total daily foraging time. Wintering pink‐footed geese Anser brachyrhynchus feeding on pastures and winter wheat fields were collected and samples of leaves in the oesophagus were measured, dried and weighed individually. We measured leaf lengths in unexploited areas of the same fields upon which geese had been feeding. Peck rates of winter wheat feeding geese were measured. Daily foraging time was obtained from observations of activity budgets of flocks of geese. Daily food intake of winter wheat feeding geese was estimated at 159–229 g ash free dry weight (AFDW) during late winter and at 188–212 g AFDW in early spring. For geese feeding on pastures in early spring food intake was estimated at 170 g AFDW. Averages were generally in accordance with estimates derived by the ‘marker substance’ method. Bite length was positively related to primary leaf length of winter wheat, suggesting that geese adjust bite size to available leaf lengths. There was a negative relationship between peck rate and length of all leaf types, but the relationship was only significant for primary leaves. Based on the assumption that bite length was identical to primary leaf length and the relationship between primary leaf length and peck rate, a quadratic relation between primary leaf length and instantaneous intake rates was derived, yielding a peak intake rate of 0.62 g AFDW min−1 at a primary leaf length of 8.4 cm. In the beginning of the winter, bite lengths were close to this optimal leaf length, but decreased during winter.

Time structure of behavioral patterns related to feed pecking in chicks

Nonrandom time patterns of pecking acts by 16 chicks were detected using the software Theme during three videotaped pecking sessions (M, C, and A). At 15 days of age pecking session, M (mash) was recorded when chicks ate a mash diet. Pecking session C (change) at 16 or 17 days of age was recorded immediately after the change of the diet to pellets presented either as regular cylinders (P) to eight chicks, or as semiovoid (Po) to eight other chicks. Pecking session A (adapted) was recorded 5 or 6 days after adaptation to P and Po. Successful (consumatory) pecks were 72%, 52%, and 61% of all pecks for sessions M, C, and A, respectively. The head of the chicks remained in a steady position between two consecutive pecks for a longer period during C (65% of the time) than M and A (54%). During C, the pecking rate was less for P (0.54 pecks/s) than for Po (0.79 pecks/s). Two consistent time patterns involving four acts frequently observed were: head rotation (or exploratory peck)⇒head in steady position⇒consumatory peck⇒head in steady position with jaw movements. Time intervals within a pattern were stable throughout sessions. However, the proportion of synchronized (included in a pattern) vs. nonsynchronized (not included in a pattern) acts decreased immediately after the change of feed form (session C). These results suggest that pecking at feed is composed of two distinct sets of acts: consistently organized patterns little affected by the form of the pecked particles and nonsynchronized acts that may be involved in sensory information.

Evidence for multistability in the visual perception of pigeons

Perceptual multistability refers to cases where perception alternates between two or more interpretations of an unchanging sensory stimulus. In a first experiment we trained eight pigeons to discriminate horizontal and vertical apparent motion stimuli and then presented a multistable display. In five cases their behavior showed alternations similar to human experiments. In a second experiment we varied the aspect ratio of the display in order to support the hypothesis of a percept-driven nature of the switching behavior. The pecking rates and mean phase durations varied as predicted. This is the first evidence of visual multistability in animals confronted with classical ambiguous figures. The data suggest a stochastic mechanism.

Pigeons Flexibly Time or Count on Cue

In Experiment 1, pigeons were presented with a sequence of light flashes and cued to peck a key for reward either after a fixed time or after a fixed number of flashes. Curves that showed the rate of key pecking over time within trials indicated that peak rates of response were reached near the fixed time on timing-cued trials and near the fixed number of flashes on counting-cued trials. In Experiment 2, the key cue was shifted from timing to counting or from counting to timing midway through a trial. The peak times reached after the cue change indicated that pigeons kept track of time while cued to count but did not count while cued to time. These findings suggest a basic asymmetry in the dual-mode model of timing and counting.

Aggressiveness in king penguins in relation to reproductive status and territory location

King penguins, Aptenodytes patagonicus, vigorously defend small territories in very dense colonies. The egg-laying season lasts approximately 4 months, but only pairs that reproduce during the first half of the period succeed in fledging a chick. I examined various factors affecting aggressiveness of king penguins during the breeding season and focused on the differences between central and peripheral territories. Pairs on peripheral territories experienced twice as many encounters with avian predators as did central birds. The vast majority of peripheral birds were late breeders, indicating that reproductive success was very low among penguins defending a territory on the edge of the colony. Time invested in territory defence and rate of agonistic encounters between breeding neighbours increased from the incubation to the brooding period. Parents gave most threat displays to territorial neighbours when the chick was very young and just before crèche formation. Distance to colony edge was not related to aggressiveness in incubating birds, however, the rate of pecking and flipper blows increased from the edge to the centre during brooding. In addition, aggressiveness of breeding penguins towards travelling birds trespassing into their territory increased with distance to edge. Early breeders were not more aggressive than late breeders but the proportion of time spent in territory defence increased with the number of days a bird had spent incubating. As expected, I did not detect any sex difference in aggressive behaviour. Birds occupying territories on the beach were generally more aggressive during the incubation period than those located on the valley sides. Reproductive status (incubating versus brooding) and territory location were the main factors explaining the various levels of aggressiveness observed in breeding king penguins.

Stress and feather pecking in laying hens in relation to housing conditions

1. Possible association between high rates of feather pecking and increased stress were investigated in laying hens. 2. From week 19 to week 30 after hatching, 16 groups of 11 hens (white Lohman Selected Leghorn hybrids) were kept in pens with or without long-cut straw as foraging material and provided with food in the form of pellets or mash. 3. Stress was assessed by egg production, weight gain, tonic immobility (TI), heterophil/lymphocyte (H/L) ratio and antibody titres to sheep red blood cells (SRBC), tetanus toxoid (TT) and human serum albumin (HSA). 4. Provision of foraging material and food form influenced feather pecking. Rates of feather pecking were highest in groups housed without straw and fed on pellets. 5. Egg production was reduced in pens without straw but not affected by food form. Both the duration of TI and H/L ratios were influenced by provision of foraging material and food form. TI was longer and H/L ratios were increased in hens housed without straw and in those fed on pellets. Antibody titers to SRBC and TT were lower in pens without straw than with straw but not influenced by food form. 6. In conclusion, foraging material and food form affected both feather pecking and indicators of stress, suggesting that feather pecking in laying hens is associated with stress.