Rate Of Pecking Research Articles

Variation of pecking rate with sward height in wild wigeon Anas penelope

We examined how pecking rate changed with sward height in wintering European wigeon Anas penelope in a nature reserve of the French Atlantic coast. Pecking rates were recorded as the time taken to perform 10 or 50 pecks. We found a negative correlation between pecking rate and sward height over a range of heights from 1.0 to 3.5 cm, but no sex effect. Equations based on the time taken to perform 10 or 50 pecks were slightly different, suggesting that scanning (scans of the sur- roundings) and moving (search for plant items of good quality) had an effect on pecking rate. However, these costs were lower (i.e. a decrease of 6-10% of pecking rate) than the effect of handling time, which remained the dominant foraging process constraining pecking rate (i.e. a decrease of 24% with each 1-cm increase in sward height).

Short-term item memory in successive same–different discriminations

Pigeons were tested in a successive same-different (S/D) discrimination procedure to examine the short-term memory for individual items in sequences of different or identical pictures. Item-by-item analyses of pecking behavior within single trials revealed this S/D discrimination emerged at the earliest possible point in the sequence--the presentation of the second item. Further, by comparing peck rates at points where different types of sequences diverged (e.g. ABA versus ABC), we determined that the pigeons remembered the first item for at least 4-8s and across one to two intervening items. These results indicate that this S/D discrimination was controlled by relational comparisons of pictorial content across memories of specific items, rather than the detection of low-level perceptual "transients" between items. A second experiment supported this conclusion by showing increased discrimination with longer first item viewing times, consistent with encoding of details about individual pictures. These findings further support a qualitative similarity among birds and primates in possessing a general capacity to judge certain types of stimulus relations, such as stimulus identity and difference. Implications for the temporal continuity of experience in animals are also considered.

Time in captivity, individual differences and foraging behaviour in wild-caught chaffinches

Wild-caught animals are often given a settling in period before experimental trials are initiated. We used wild-caught chaffinches (Fringilla coelebs) to investigate (a) the effect of settling in period duration on the likelihood that chaffinches foraged during experimental trials and (b) whether settling in period duration influenced measures of foraging and vigilance behaviour recorded from those experiments. The probability of collecting foraging data from an individual's first trial fell below 50% if it had been in captivity for more than 12 days prior to that trial, whereas the probability was >75% if trials were completed within two days of capture. The successful collection of foraging data from subsequent trials was also dependent on the number of days an individual spent in captivity prior to its first trial and on whether that individual foraged in its first trial, suggesting that some individuals were more inclined to forage in captivity. Individuals that foraged in their first trial had a 94% higher success rate in subsequent trials than those that did not. However, settling in period duration did not significantly influence the peck rate, mean search period or mean vigilance period of individuals that did forage. Our results show that allowing a settling in period actually reduced the likelihood of collecting foraging data from chaffinches and that commencing experiments shortly after capture increased data collection efficiency. We discuss the possibility that the inability to collect data from certain birds following a settling in period could lead to potentially important biases in results, particularly if propensity to forage is linked to an individual's coping strategy or personality. We conclude that it may not always be beneficial to allow wild-caught animals to habituate to captivity before commencing experiments. In some cases, testing animals soon after capture may increase the likelihood of data collection, reducing both the number of study animals required and the length of time they spend in captivity.

Commensal Association of Waterfowl with Feeding Swans

The commensal association of waterfowl with foraging swans (Cygnus spp.) was studied in southernmost Sweden. Among more than 1,500 Mute Swans (C. olor) only 2.6% had attending waterfowl whereas 41% of Whooper Swans (C. cygnus) and 51% of Tundra Swans (C. columbianus bewicki) had associated commensals, no doubt because of the species’ different feeding techniques. Four species of commensals occurred at the main study site, Eurasian Wigeon (Anas penelope), Mallard (A. platyrhynchos), Pochard (Aythya ferina) and Common Coot (Fulica atra), wigeon making up about a third of the individuals. A mean of 3.4 waterfowl attended each Whooper Swan. Aggression was common among the commensals, with intraspecific aggression being more common than interspecific aggression in both wigeon and Pochard, and apparently influenced the size and composition of the groups and also the individuals’ positions relative to the swan. The preferred position just behind the swan was defended by threats and attacks. Although wigeon in this position did not have higher pecking rates they obtained significantly more large items than wigeon farther behind the swan.

Low Foraging Success of Semipalmated Sandpipers at the Edges of Groups

AbstractVariation in foraging success in relation to spatial position in a group is little known in species that feed on mobile prey that can hide or flee upon disturbance by foragers. I examined the foraging success of individuals located either at the edge or at the centre of flocks of semipalmated sandpipers (Calidris pusilla) feeding on a burrowing amphipod (Corophium volutator) during migration stopover in the Bay of Fundy, Canada. The rates of pecking, prey capture and success were lower for individuals foraging at the edge than at the centre of flocks. Edge birds spent more time running and more time flying than centre birds. Edge birds moved away from the centre of the flock and made frequent short flights towards the centre. In contrast, centre birds rarely moved in a specific direction and flew mostly to relocate elsewhere with the whole flock. Sandpiper flocks foraged over a large area in a relatively short amount of time. In addition, amphipod density is high in this habitat. It thus appears unlikely that prey depletion or low food availability at the edges of groups could explain the spatial variation in foraging success. Low foraging success at the edges of flocks thus arose mainly because of time costs related to flock expansion and retraction. The effect of mutual interference among foragers and of predation risk by falcons is discussed with respect to flock expansion and retraction.

Pre- and post-hatching effects of corticosterone treatment on behavior of the domestic chick

We investigated the effect of 60 ìg of corticosterone administered to domestic chicks either before or after hatching on the behavioral response to isolation in a novel arena and performance in a task involving the simultaneous identification of food and detection of a predator (overhead silhouette of a hawk moving overhead). Following release into a novel arena, chicks treated with corticosterone at 18 days of incubation emitted more distress vocalizations. In contrast, no difference in the number of vocalizations was found between chicks treated with corticosterone at day 1 post-hatching and controls. Behavior in the home cages was generally similar across treatments, though chicks treated with corticosterone at 18 days of incubation slept more than control chicks. While searching for grain against a background of pebbles, chicks treated with corticosterone at embryonic day 18, but not chicks treated on day 1 post-hatching, took longer to detect the overhead image of a predator than did controls. Corticosterone treatment at both ages increased the rate of pecking at grains and pebbles. Our findings support work on other birds indicating that corticosterone treatment during incubation influences stress reactivity. The impairment in predator detection in chicks treated with corticosterone on day 18 of incubation appears to be caused by the known effects of corticosterone treatment at this age in preventing the development of lateralization of the thalamofugal visual projections. This further supports the hypothesis that brain lateralization provides an advantage in performing more than one task simultaneously.

Importance of drainage channels for waders foraging on tidal flats: relevasnce for the management of estuarine wetlands

Summary Despite covering a relatively small area on a global scale, estuarine tidal flats are vital to many aquatic bird species during much of the yearly cycle. Small‐scale features of tidal flats, such as water drainage channels, can influence the carrying capacity of estuarine wetlands, yet their ecological impact is poorly understood. In this study we evaluated the influence of drainage channels on the quality of feeding habitat for waders in the Tagus estuary, Portugal. We measured the abundance of seven wader species at five distance classes from drainage channels, and analysed the variation in peck rates, step rates, turning rates and success rates. In addition we measured the density of macroinvertebrate prey and the sediment physical–chemical characteristics at different distances from the channels. All wader species occurred at higher densities near the channels. In the study area 44% of the birds fed on just 12% of the available surface, less than 5 m away from drainage channels. Wader foraging behaviour also suggests a greater feeding effort near the channels. While the characteristics of the sediments did not change significantly with distance from channels, prey abundance corresponded closely with wader abundance, suggesting that the small scale distribution of birds on the tidal flats may be related to the presence of their prey. Synthesis and applications. Our study shows that the areas around drainage channels are particularly important feeding sites for waders foraging on tidal flats. Consequently, managers of estuarine wetlands should strive to preserve or improve channel networks. This can be achieved by (i) preserving saltmarshes and saltpans adjacent to tidal flats, (ii) minimizing the reclamation of upshore flats and (iii) avoiding embankments and canalizations of inland water flows that reduce the number of water entry points onto tidal flats.

The temporal development and sensory mediation of social discrimination in domestic chicks

We conducted a series of experiments to investigate the temporal development and sensory basis of social discrimination by young chicks, Gallus gallus domesticus. In the initial experiment, 1-day-old chicks were housed in pairs for 6–9 or 11–14 h. After this treatment period, interactions between paired chicks that had been housed together for 6–9 h did not differ from those of unfamiliar chicks. However, pairs of chicks that had been together for 11–14 h pecked each other significantly less than did unfamiliar pairs. Reduced pecking by the familiar partners indicates that 11–14 h of direct contact is sufficient for the establishment of individual discrimination. In a second experiment we assessed the role of olfaction in the development of social discrimination. Chicks in the anosmic condition were housed in pairs after their external nares were blocked with acrylic cement. Control chicks had cement applied to the beak (the nares remained uncovered) before being housed in pairs. When tested after the pair-housing period, pecking frequencies were lower among familiar cagemates than among unfamiliar pairs of chicks in both the anosmic and control conditions. Anosmic chicks, unlike the controls, showed little reaction to mint odour, thereby verifying that the blocked-nares treatment disrupted olfactory perception. In a final experiment, there was no reliable difference between the pecking rates of paired chicks that had been housed together in the dark and those of unfamiliar dark-reared pairs. We conclude that access to social partners' visual phenotype, but not olfactory familiarization, is necessary for the rapid development of individual discrimination by chicks.

Factors Affecting the Foraging Behavior of the Squacco Heron

Abstract The foraging behavior of adult and recently fledged juvenile Squacco Herons (Ardeola ralloides) was studied during the breeding season at the Axios Delta, northern Greece. Adults were more efficient foragers than young birds and they had a 37% higher success per peck rate. The majority of adults captured some large prey items, while most juveniles caught only small prey. A comparison between the two age classes, as well as seasonal trends in adult data, indicated a negative association between prey size and foraging rates. Adult and juvenile foraging behavior did not vary significantly between morning and evening. Herons that moved faster also had higher pecking and capture rates, but a lower success ratio. Moving rate did not appear to be correlated with prey size. Herons moved at a slower rate along the edge of dense reed beds, probably in response to this habitat’s physical structure. Adults caught a greater proportion large prey items in open-water areas than in areas with more vegetation.

Has habitat degradation affected foraging behaviour and reproductive success of lesser snow geese (Chen caerulescens caerulescens)?

:Some individuals respond to habitat degradation by dispersing to less degraded areas while others remain but display altered behaviours, potentially compensating for the habitat change. We examined the latter possibility by evaluating foraging behaviour and size of lesser snow geese over a period during which their habitat became severely degraded. We show that in this now-degraded habitat, adults spend more of their total time in motor activities and less time in vigilance and comfort behaviours. Goslings spend less of their total time foraging and more in comfort and other behaviours. The pecking rate of both adults and goslings while foraging increases, as do motor and searching behaviours of adults. These changes have not enabled the birds to keep pace with the loss of vegetation, and the size of goslings has continued to decline, likely leading to a reduction in reproductive success. The persistent use of degraded salt marsh is probably related to philopatry and will further damage the marsh.

Biological and Economic Effects on Responding:Rate and Duration of the Pigeon's Key Peck

Pigeons were studied on a two-component multiple schedule in which key pecking 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. In addition to rate, duration of key pecks was measured in an attempt to differentiate the biological and economic effects on key pecking. When components alternated frequently (every 10 s), all pigeons key pecked at a much higher rate during the component with the additional food deliveries, whether response dependent or 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 when the additional food was response dependent. The additional food deliveries, whether response-independent or response-dependent, however, had no consistent effect on the pigeon's key-peck duration. That is, there were no systematic or reliable shifts in peck duration as would be predicted if short-duration pecks were biologically based. Despite the fact that we were unable to “tag” the biological effect in terms of key-peck duration, the finding that the delivery of response-independent food has different, but predictable effects on responding suggests that animal learning principles can be integrated with species-typical, biological considerations without the need to propose constraints that limit general laws of learning.

Differential reinstatement predicted by preextinction response rate

Reinstatement refers to the recovery of previously extinguished responding by the response-independent delivery of a stimulus that was a reinforcer in training. Two experiments were conducted to examine relative reinstatement following the training of differential preextinction response rates, either with equal (Experiment 1) or unequal (Experiment 2) preextinction reinforcement rates. In Experiment 1, each of 3 pigeons first pecked at relatively high rates in the tandem variable-time 117-sec fixed-interval 3-sec component of a multiple schedule and at lower rates in a separate tandem variable-interval 117-sec fixed-time 3-sec component. Reinforcement rates were equal between components. Pecking then was extinguished in each component, before being reinstated under a multiple variable-time 120-sec variable-time 120-sec schedule. Greater reinstatement occurred in the component previously correlated with higher rates of pecking. In Experiment 2, in an initial condition, the mean rate of lever pressing for one group of 8 rats was significantly higher under a fixed-ratio 3 schedule than for another group of 8 rats under a fixed-ratio 1 schedule. Mean reinforcement rate was significantly higher for the group exposed to the fixed-ratio 1 schedule. For each group, lever pressing then was extinguished, before being reinstated under a variable-time 30-sec schedule. Significantly greater mean reinstatement occurred for the group previously exposed to the fixed-ratio 3 schedule. These results suggest that differential reinstatement may be predicted by preextinction response rate, perhaps independently of preextinction reinforcement rate.

Quantifying the effects of habitat structure on prey detectability and accessibility to farmland birds

For species that rely on visual cues to detect prey items, increasing the structural complexity of a patch can greatly influence forager behaviour through consequent reductions in prey detectability and accessibility. These effects are likely to manifest themselves in terms of foraging site selection and there is plentiful evidence for preferential site selection for a suite of taxa. However, the underlying effects of habitat structure on foraging behaviour, which are likely to drive these observed site selections, are much less well understood. We present the results of two studies designed to quantify the effects of vegetation structure on prey detectability and accessibility to avian invertebrate feeders and granivores on farmland. There was a significant negative relationship between potential prey detectability and both distance and vegetation height in cereal crops and stubbles for Northern Lapwings Vanellus vanellus. The interscan distance travelled by Lapwings differed significantly between habitats, with longer distances travelled in cereal crops and harrowed compared with ploughed soil and grasses. The peck rate, head‐up rate and mean search period of foraging Chaffinches Fringilla coelebs were not affected by increasing vegetation structure but forager mobility was significantly reduced. We hope that by quantifying the effects of vegetation structure on prey detectability and accessibility we can highlight the importance of considering these factors, as well as prey abundance, when developing management strategies for farmland birds.

The effect of limited visibility on vigilance behaviour and speed of predator detection: implications for the conservation of granivorous passerines

Foraging animals frequently change their pattern of vigilance when they move from a patch with a clear view to one with a relatively obstructed view. This has been widely interpreted as compensation for a reduced ability to detect approaching predators in obstructed habitats. We test the extent to which changes in vigilance may compensate for the effect of reduced visibility on an animal's ability to detect predators. We measured the vigilance, foraging and speed of predator‐response behaviours of lone chaffinches Fringilla coelebs that fed on seeds (800 per m2) scattered on artificial stubble habitats (with either a clear view of surroundings or an obstructed view). On both treatments, individuals with more rapid head‐up rates responded more quickly to a flying model sparrowhawk Accipiter nisus (P=0.04); as did individuals with shorter food‐search times (P=0.02). However, neither head‐up rate nor food‐search period varied with obstruction. Based on research previously published using this system, we suggest that this is because individuals are constrained in their ability to increase head‐up rate because doing so is largely determined by their individually determined foraging efficiency. Instead chaffinches increased the duration of their head‐up periods by 13% in the visually obstructed treatment (long stubble) and peck rates were 13% lower. Despite this presumed attempt to compensate for reduced visibility, duration of head‐up period had no effect on response time of the fast‐moving predator in our experiment and birds were 24% slower to respond in the long stubble. Rather than being maladaptive, increasing head‐up duration may have been related to enhanced detection of other predator types, for example stalkers. Our results have implications for the conservation of wild granivorous birds. They support the view that agroeconomic decisions that affect micro‐habitat structure over a large scale could affect predation risk, habitat choice and the conservation status of granivorous birds.

Dustbathing by broiler chickens: a comparison of preference for four different substrates

Leg abnormalities leading to lameness in broiler chickens are a serious welfare problem. Previous work in our laboratory demonstrated that providing broiler chickens with the opportunity to exercise by performing more natural behaviors (such as perching, walking up and down inclines and dustbathing) can improve their ability to walk normally [J.A. Mench, J.P. Garner, C. Falcone, Behavioral activity and its effects on leg problems in broiler chickens, in: H. Oester, C. Wyss (Eds.), Proceedings of the Sixth European Symposium on Poultry Welfare, World’s Poultry Science Association, Zollikofen, Switzerland, 2001, pp. 152–156]. With the long-term goal of stimulating dustbathing to improve leg condition, the aim of this study was to determine the dustbathing substrate preferred by broiler chickens. We conducted a dustbathing choice test experiment using four different bedding types (pine wood shavings, rice hulls, construction grade sand, and a recycled paper animal bedding product). Four different broiler chickens were tested each week for 6 weeks starting when the chicks were 1 week old. They were selected from two groups of broiler chickens housed in large home pens bedded with wood shavings. Selected birds were tested in smaller pens where they were deprived of all loose bedding material except during testing, which was carried out for 1 h each day for three consecutive days per week. During an observation, each corner of the test pen was filled with a different bedding type, and the behavior of the focal chick recorded. Vertical wing shakes (VWS) were used as the primary measure of dustbathing activity. Broilers performed significantly more VWS per hour in sand ( F 3,36 =13.52, P <0.0005) and spent a greater proportion of their total time in sand ( F 5,60 =5.15, P =0.001) than in the rice hulls, paper, or wood shavings. They also visited the sand significantly more often than the paper or the wood shavings ( F 5,60 =96.47, P <0.0005). There were no dustbaths in the rice hulls. The latency to enter sand was significantly shorter than the latency to enter any of the other three substrates ( F 3,15 =5.24, P =0.0113). Ground pecking generally precedes a dustbathing bout, and the rate of pecking and the proportion of the total time budget spent pecking were also highest for sand ( F 3,51 =24.49, P <0.0001 and F 3,51 =15.28, P <0.0001, respectively). The preference for sand was apparent in the first week, and was stable with age. The results of this study suggest that sand is attractive to broiler chickens and is a potent stimulus for dustbathing. Further work is needed to determine if stimulating broiler chickens to dustbathe by providing sand can improve their leg condition, and thus their welfare.

Within-session delay-of-reinforcement gradients.

Within-session delay-of-reinforcement gradients were generated with pigeons by progressively increasing delays to reinforcement within each session. In Experiment 1, the effects of imposing progressive delays on variable-interval and fixed-interval schedules were investigated while controlling for simultaneous decreases in reinforcer rate across the session via a within-subject yoked-control procedure. Rate of key pecking decreased as a negatively decelerated function of delay of reinforcement within a session. These rate decreases were greater than those during a yoked-interval session in which the rate of immediate reinforcement decreased at the same rate as it did under the progressive-delay procedure. In Experiment 2, delay-of-reinforcement gradients were shallower when the progressive delay intervals were signaled by a blackout than when they were unsignaled. The delay gradients obtained in each experiment were similar to those generated under conditions in which different delays of reinforcement are imposed across blocks of sessions. The present procedure offers a technique for rapidly generating delay-of-reinforcement gradients that might serve as baselines for assessing the effects of other behavioral and pharmacological variables.

Predation on artificial nests in post-mining recultivated area and forest edge: contrasting the use of plasticine and quail eggs

Intensive opencast coal mining has been in effect in the northeastern outskirts of Pécs (south Hungary) since 1968. The covering layer of the northern, recultivated area extending over 15 ha is overgrown by herbaceous vegetation. Oleaster ( Elaeagnus angustifolia) was planted in rows on the hillsides. The recultivated open areas are bordered by turkey oak forests ( Potentillo micranthae– Quercetum daleschampii Horvát A.O. 1981) from the east, north, and west; thus it forms a wedge of a clearing in the wood. Our studies have aimed at determining whether nest predation is greater in the forest edge or in the rows of oleaster in the recultivated area. First a plasticine egg, then a quail egg was put in each of the 50–50 artificial nests mounted on trees in the two habitat types. After a week it was found that predation to nests with only one plasticine or one quail egg in each was significantly higher in forest edge trees than in the rows of oleaster. There was no significant difference between predation to plasticine and quail eggs in either of the habitats. Irrespective of where the nests were, predators (mostly jays, tits, and once a small mammal) attempted to “consume” the plasticine eggs in the nest, whereas quail eggs were usually taken away. The rate of disappearance of eggs from the nests (plasticine 24%, quail 60%) differed significantly from the rate of pecking or gnawing at them and from in situ consumption (plasticine 76%, quail 40%). Nests located in tree rows in the recultivated areas are safer than those in the forest edge.

Dustbathing by broiler chickens: a comparison of preference for four different substrates

Leg abnormalities leading to lameness in broiler chickens are a serious welfare problem. Previous work in our laboratory demonstrated that providing broiler chickens with the opportunity to exercise by performing more natural behaviors (such as perching, walking up and down inclines and dustbathing) can improve their ability to walk normally [J.A. Mench, J.P. Garner, C. Falcone, Behavioral activity and its effects on leg problems in broiler chickens, in: H. Oester, C. Wyss (Eds.), Proceedings of the Sixth European Symposium on Poultry Welfare, World’s Poultry Science Association, Zollikofen, Switzerland, 2001, pp. 152–156]. With the long-term goal of stimulating dustbathing to improve leg condition, the aim of this study was to determine the dustbathing substrate preferred by broiler chickens. We conducted a dustbathing choice test experiment using four different bedding types (pine wood shavings, rice hulls, construction grade sand, and a recycled paper animal bedding product). Four different broiler chickens were tested each week for 6 weeks starting when the chicks were 1 week old. They were selected from two groups of broiler chickens housed in large home pens bedded with wood shavings. Selected birds were tested in smaller pens where they were deprived of all loose bedding material except during testing, which was carried out for 1 h each day for three consecutive days per week. During an observation, each corner of the test pen was filled with a different bedding type, and the behavior of the focal chick recorded. Vertical wing shakes (VWS) were used as the primary measure of dustbathing activity. Broilers performed significantly more VWS per hour in sand ( F 3,36=13.52, P<0.0005) and spent a greater proportion of their total time in sand ( F 5,60=5.15, P=0.001) than in the rice hulls, paper, or wood shavings. They also visited the sand significantly more often than the paper or the wood shavings ( F 5,60=96.47, P<0.0005). There were no dustbaths in the rice hulls. The latency to enter sand was significantly shorter than the latency to enter any of the other three substrates ( F 3,15=5.24, P=0.0113). Ground pecking generally precedes a dustbathing bout, and the rate of pecking and the proportion of the total time budget spent pecking were also highest for sand ( F 3,51=24.49, P<0.0001 and F 3,51=15.28, P<0.0001, respectively). The preference for sand was apparent in the first week, and was stable with age. The results of this study suggest that sand is attractive to broiler chickens and is a potent stimulus for dustbathing. Further work is needed to determine if stimulating broiler chickens to dustbathe by providing sand can improve their leg condition, and thus their welfare.

Nutmeg mannikins ( Lonchura punctulata) reduce their feeding rates in response to simulated competition.

Group feeding animals experience a number of competitive foraging costs that may result in a lowered feeding rate. It is important to distinguish between reductions in feeding rates that are caused by reduced food availability and physical interactions among foragers from those caused by the mere presence of foraging companions that may be self-imposed in order to obtain some benefit of group membership. Starlings ( Sturnus vulgaris) reduce their feeding rates when in the company of simulated competitors located in an adjacent cage that cannot affect the food availability or interact with the forager. In the present study, we investigate whether the presence of simulated competitors in another species of passerine, nutmeg mannikins ( Lonchura punctulata), can result in self-imposed reductions in feeding rates. When feeding in the company of simulated competitors, mannikins spent more non-foraging time near them, fed more slowly, reduced travel times between patches, reduced their scanning time and pecked more slowly. These results provide evidence that simulated competitors induce a reduction in pecking rate: behavioural interference. These self-imposed responses to competitors may have resulted from attempts to remain close to the non-feeding companions. Such self-imposed reductions in feeding rates may be a widespread yet generally unrecognised foraging cost to group feeding individuals.

Dynamics of Foraging Behavior Associated With Variation in Habitat and Forage Availability in Captive Black Brant (Branta Bernicla Nigricans) Goslings in Alaska

Abstract We conducted an experiment to study the effect of gosling density on food abundance and feeding behavior of Black Brant (Branta bernicla) goslings in two habitat types important to Black Brant on the Yukon-Kuskokwim Delta, Alaska: (1) Carex subspathacea grazing lawns and (2) slough levees that contain Triglochin palustris. Within each habitat, we manipulated grazing pressure by allowing goslings to graze specific plots every 6, 9, or 12 days. We randomly assigned six goslings to one of six treatment groups (three grazing frequencies × two habitats). Biomass of C. subspathacea was higher in lightly grazed plots (grazed every 12 days) than in the heavily grazed plots (grazed every 6 days). Offtake in C. subspathacea was also greater in the lightly grazed plots. Within C. subspathacea stands, proportion of time spent feeding varied among grazing intensities. Goslings within heavily grazed plots spent more time feeding than goslings in lightly grazed plots. Within slough levee habitat, there were no differences between heavily and lightly grazed plots in either biomass or offtake of T. palustris. Whereas overall percentage of time feeding did not vary between the two habitats, percentage of time feeding declined as gosling mass increased in all treatments and habitats. Although the trend in peck rate over time varied among treatments and between habitats, during trials very early in the season we observed a reduced peck rate in the heavily grazed treatment, but only within the C. subspathacea grazing lawns. There was no variation in peck rate among treatments within slough levee habitat; however, peck rates for goslings fed on C. subspathacea was double the rate of goslings in slough levee. Thus, the varied growth responses of plants between habitats to variation in grazing pressure that we observed during this experiment suggest the importance of density-dependent effects on brood-rearing habitat and the resulting variation in gosling growth.