Vigilance during food handling by Oystercatchers Haematopus ostralegus reduces the chances of losing prey to kleptoparasites

Oystercatchers Haematopus ostralegus periodically pause while handling mussels Mytilus edulis to make visual scans. This paper presents evidence that scanning is associated with the high incidence of intra-specific food stealing among mussel-eating Oystercatchers. Scanning increased in frequency as bird density - and the risk of being attacked for mussels increased and the duration of attacks decreased. Additionally, among a sample of individually marked adults, the aggressive dominant birds spent half as much time scanning as the less aggressive subdominants and were also less likely to be attacked. Whereas detecting an attack made no difference to the success with which the dominants defended their mussels, subdominants increased their chances of retaining the mussel if they detected and carried the mussel away from the approaching attacker. The extra time which the less aggressive birds spent in vigilance seems best understood as a tactic for reducing food loss to kleptoparasites.     

Agonistic experience and individual recognition in male Quelea quelea

Male $\text{Quelea}$ were moved between groups to assess whether experience of winning or losing in new groups was correlated with their success in competition over food when they were returned to their original groups. No such effect was found. However, differences in time spent feeding after deprivation and in aggressive behaviour were found between groups depending on whether they were made up from high- or low-ranking individuals. In paired encounters there was no evidence that birds threatened unfamiliar individuals more than familiar ones or that they avoided sitting next to them more than familiar birds. This suggests that individual recognition, if it exists at all in these groups, is not important in their agonistic relationships. The rank birds occupied was correlated with beak colour, a probable measure of androgen levels, and with the amount of food consumed after deprivation. The latter result suggests that the same period of deprivation may affect some individuals more than others and this in turn may lead them to compete more for food.     

Piping as a display of dominance by wintering Oystercatchers Haematopus ostralegus

Although Oystercatchers Haematopus ostralegus wintering in the Exe Estuary performed the piping display in any type of aggressive encounter, it was predominantly observed in two contexts. ‘Solitary piping’ occurred when one individual piped without an obvious opponent being in the immediate vicinity. In ‘piping ceremonies’, two or more individuals piped at each other for prolonged periods at close distance. Prolonged contests over mussels were usually won by the individual that had initially started piping. The most aggressive and successful birds (the dominants), engaged most often in solitary piping and piping ceremonies, using up to 10% of their time this way. This suggests that the behaviour was associated with dominance rank. The hypothesis is that the two birds are likely to start piping if their relative status has not already been established, so that a quick end to a dispute over a mussel or feeding site is not achieved. A dominant individual performs solitary piping from a distance to suppress the aggressive activities of other birds within its feeding range. If this signal fails, the dominant may join the ceremony, explaining why three was the most frequent number of birds involved in piping ceremonies. The ‘butterfly’ flight, used mainly by apparently dominant birds as they arrived on the feeding grounds, may signal their high status to birds already there. The outcome of several piping ceremonies involving birds of known dominance was consistent with this explanation. The location of piping ceremonies involving only two birds (interpreted as piping ceremonies not joined by dominants) at the extremities of the feeding ranges of the most dominant individuals is also consistent with this hypothesis, because this is where their dominance would be expected to decline and would therefore be more likely to be contested. This explanation of piping and butterfly displays assumes that individuals can recognize other individuals or quickly assess their dominance. Since dominant individuals were attacked less often than subdominants and attacking birds were rebuffed less than would be expected if recognition did not occur, we suggest that some form of dominance or individual recognition did exist. The width of the white collar did not correlate with dominance, but the individual variations in this feature may enable birds to distinguish each other and thus learn their relative status. It is intriguing that the diplomatist posture, which is typically used to rebuff misguided attackers, seems almost designed to give the opponent a particularly clear view of the white collar.     

BREEDING OF THE WHITE-BACKED AND RÜPPELL'S GRIFFON VULTURES, GYPS AFRICANUS AND G. RUEPPELLII

The breeding season of two species of griffon vultures are described. Rüppell's Griffon Vulture lays 2–3 months earlier than the White-backed Griffon. Young birds were hand-reared to determine their food requirements during growth; these estimates were combined with the food requirements of adult birds to make an estimate of the amount of food a parent bird needs to obtain when it is rearing young. The amount of food actually obtained by a group of birds was recorded from the size of the crops of birds returning to the breeding colony in the afternoon. The comparison of the estimates of the food obtained and the food required through the breeding season suggested that there may be a period during rearing when there was insufficient food available to satisfy the food requirements of both chick and adult. Chicks were found to have a very high survival rate and were probably receiving sufficient food. Presumably adult birds were not therefore receiving sufficient food, and the examination of a sample of adult birds for body condition through the breeding season showed a clear decline in their fat deposits. It was considered that in both species, breeding was timed so that the young left the nest at a period in the year when food conditions were good and the young birds could feed with little competition from adults. The parent birds therefore had to rear young during a season in the year when food conditions were not always adequate and they had to rely on utilising fat reserves. The food conditions for vultures during this study were probably favourable and during years of food shortage breeding may become impossible, or restricted to the most aggressive and dominant individuals.     

Prey abundance and the strength of interference in a foraging shorebird

Interference is an important component of food competition but is often difficult to detect and measure in natural animal populations. Although interference has been shown to occur between oystercatchers Haematopus ostralegus L. feeding on mussels Mytilus edulis L., four previous studies have not detected interference between oystercatchers feeding on cockles Cerastoderma edule L. In contrast, this study detected interference between cockle-feeding oystercatchers in the Baie de Somme, France. Prey stealing (kleptoparasitism), one of the main causes of interference between mussel-feeders, also occurred between oystercatchers in the Baie de Somme. The kleptoparasitism rate was related to the natural variation in the food supply, tending to be higher when cockles were rare. Feeding rate was negatively related to competitor density, so providing evidence for interference, but, as in mussel-feeders, only above a threshold density of about 50–100 birds ha⁻¹. The strength of interference at a fixed competitor density was related to the cockle food supply, usually being greater when cockles were rare. Previous studies probably failed to detect interference between cockle-feeders because competitor densities were too low, or cockles were too abundant, or because they were not conducted during late winter when interference is most intense. The study shows that natural variation in the food supply can influence the strength of interference within an animal population and provides support for those behaviour-based interference models which predict that the strength of interference will be greatest when competitor densities are high and prey scarce.     

Individual and age differences in the feeding ecology of Oystercatchers Haematopus ostralegus wintering on the Exe Estuary, Devon

The habitats and foods used by a sample of marked individuals and by the whole population of Oystercatchers Haematopus ostralegus wintering on the Exe estuary, South Devon, are described. In the spring and early summer, only a few hundred immatures were present. Two thousand adults and several hundred juveniles arrived in late summer from the breeding grounds and remained until the following spring. The majority of the birds were then adults. At low water, most adults fed on the mussel Mytilus edulis beds and ate mussels. Most individuals specialised on this prey and ate little else. Some adults fed on mud-flats and sandflats within the estuary and along the coast, and specialised on a mixture of Nereis diversicolor and Scrobicularia plana or on Cerastoderma edule or Littorina spp. Though some juveniles ate mussels from the time they arrived, most did not. In winter, they took Scrobicularia on mudflats, earthworms Lumbricidae and leatherjackets Tipulidae larvae in fields and Spisula and mussels along the coast. At other times of year they mainly ate Nereis. However, as they grew older, more birds began to specialise on mussels, especially in their second, third and fourth summers when the adults were away. At high water, most birds roosted at the mouth of the estuary or along the coast. However, several hundred fed in the fields in winter with more doing so late in the winter on warm days on Neap tides when less time was available for feeding on the estuary in daylight. Birds feeding on Nereis and Scrobicularia at low water were most often seen in the fields, irrespective of age. Birds feeding on Mytilus and Littorina occurred there rarely, but no bird eating Cerastoderma was seen there. The findings are discussed in relation to age differences in feeding skills and ability to compete successfully with other birds.     

Unequal food distribution among great egret Ardea alba nestlings: parental choice or sibling aggression?

In broods of great egrets Ardea alba and other birds with siblicidal nestlings, the first-hatched brood members generally secure far more food than do their juniors. This feeding advantage could be caused by parental favoritism, or by seniors attacking and thereby dominating their juniors. We investigated these possibilities by comparing how fathers and mothers allocated food among their offspring when chicks were free to fight versus when they were physically separated by a Plexiglas barrier. When free to fight, dominant nestlings received significantly more food than did their subordinates. When nestlings were separated, mothers, but not fathers, delivered significantly more food per meal to the β (second-ranked) chick than to other nestlings. This is the first experimental evidence of differential feeding by parents in a species with aggressive nestlings.     

The effect of kleptoparasite and host numbers on the risk of food‐stealing in an avian assemblage

Kleptoparasitism involves the theft of resources such as food items from one individual by another. Such food‐stealing behaviour can have important consequences for birds, in terms of individual fitness and population sizes. In order to understand avian host–kleptoparasite interactions, studies are needed which identify the factors which modulate the risk of kleptoparasitism. In temperate European intertidal areas, Eurasian oystercatchers Haematopus ostralegus feed primarily on bivalve molluscs, which may be stolen by kleptoparasitic species such as carrion crows Corvus corone and herring gulls Larus argentatus. In this study we combined overwinter foraging observations of oystercatchers and their kleptoparasites on the Exe Estuary, UK, with statistical modelling to identify the factors that influence the likelihood of successful food stealing behaviour occurring. Across the winter, 16.4% of oystercatcher foraging attempts ended in successful kleptoparasitism; the risk of theft was lowest in February (10.8%) and highest in December (36.3%). Using an information theoretic approach to compare multiple logistic regression models we present evidence that the outcome of host foraging attempts varied with the number of kleptoparasites per host within the foraging patch for two out of five individual months, and for all months grouped. Successful, kleptoparasitism was more likely to occur when the total number of all kleptoparasites per host was greater. Across the entire winter study period, oystercatcher foraging attempts that resulted in kleptoparasitism were associated with a mean number of kleptoparasites per host that was more than double that for foraging attempts that ended in the oystercatcher successfully consuming the mussel. Conversely, the stage of the tidal cycle within the estuary did not affect the outcome of oystercatcher foraging attempts. Our study provides evidence that bird numbers influence the risk of kleptoparasitism within avian assemblages.     

Food stealing in cockroaches

Relationships between food stealing and exploitation of main food sources were investigated in the German cockroach,Blattella germanica (L.) (Dictyoptera: Blattellidae). The occurrence of food stealing during food exploitation was associated with the course of depletion of the main food sources and not with spatial distribution or distance from shelter. Stolen pieces of food always appeared towards the end of exploitation of a food source. Their occurrence appeared to be a consequence of the exploitation of a food source rather than a specific strategy. The proportion of animals of different developmental stages observed with stolen pieces differed significantly from that in the general population. There were proportionally more males, females and large larvae and proportionally less small larvae with stolen pieces than on the main food source. These data suggest that stolen pieces appeared when competition for access to food increased, and that larger cockroaches (adults and larger larvae) were then dominant and benefited from monopolizing stolen pieces of food.     

Dominance rank influences food hoarding in New Zealand Robins Petroica australis

Social interactions are thought to be an important determinant of food hoarding behaviour in birds. Theoretical work predicts that subordinate birds should cache more to offset losses to dominant birds. However, empirical support for this prediction is mixed. We evaluated whether social dominance influences the food hoarding behaviour of New Zealand Robins Petroica australis . Robins provide a unique opportunity to test food hoarding theory because they are fearless of humans and will cache food presented to them by hand. We offered mealworms to free-ranging male and female Robins to test whether (1) one sex was socially dominant, (2) the subordinate sex cached more frequently than the dominant sex and (3) birds cached more frequently when they were in the presence of a potential competitor. Our results indicate that males were dominant over females. Males acquired most of the prey offered to birds during trials and won all aggressive encounters observed between sexes. However, caching rates ran contrary to theoretical predictions. Males stored approximately twice as many mealworms as females. Both sexes also stored more food when they were alone than when they were accompanied by conspecifics. We interpret the reluctance of females and paired birds to hoard food as a strategy to avoid the loss of caches to competitors. Our overall results indicate that dominance rank strongly influences caching decisions, but that caching rates ran contrary to theoretical predictions.     

Mirror-mediated responses of California scrub jays (Aphelocoma californica) during a caching task and the mark test

Mirror self-recognition, as an index of self-awareness, has been proposed as a precursor for more complex social cognitive abilities, such as prosocial reasoning and cooperative decision-making. Indeed, evidence for mirror self-recognition has been shown for animals possessing complex social cognitive abilities such as great apes, dolphins, elephants and corvids. California scrub jays (Aphelocoma californica) have provided strong evidence that non-human animals are capable of mental state attribution. For instance, scrub jays are reported to use their experience stealing the food of others to infer that other birds may similarly intend to steal from them. If a concept of “self” is required for such complex social cognitive abilities, then scrub jays might be expected to show mirror self-recognition. Thus, we examined whether California scrub jays are capable of mirror self-recognition using two experimental contexts: a caching task and the mark test. During the caching task, we compared the extent to which scrub jays protected their food after caching alone, in the presence of a conspecific and in the presence of a mirror. The birds did not engage in more cache protection behaviours with a mirror present than when caching alone, suggesting scrub jays may have recognized their reflection and so did not expect cache theft. Alternative explanations for this behaviour are also discussed. During the mark test, the scrub jays were surreptitiously marked with a red or plumage-coloured control sticker. The scrub jays showed no evidence of mirror self-recognition during the mark test, as the birds did not preferentially attempt to remove the red mark in the presence of a mirror. Together, the results provide mixed evidence of the mirror self-recognition abilities of California scrub jays. We highlight the need to develop alternative approaches for evaluating mirror self-recognition in non-human animals to better understand its relationship with complex social cognition.     

Salinity as a constraint affecting food and habitat choice of mussel-feeding diving ducks

Observations of freshwater drinking in Eiders feeding primarily on mussels led us to hypothesize that the highly saline sea water enclosed in mussels could cause salt-related dehydration problems in the ducks, since they consume entire mussels. The proportion of sea water increases with increasing mussel size. Smaller duck species are more sensitive to the higher salt content of larger mussels than are larger ducks; however, salt stress may be avoided by feeding in habitats with lower salinity, by feeding on less salty food items, by utilizing smaller mussels, by drinking fresh water, or by employing low energy foraging techniques. A possible evolutionary strategy for solving the salt problem might be to increase body mass, enabling ducks to utilize larger mussels without passing an upper salt consumption limit. At the same time, foraging on larger mussels is more economical. Although large size facilitates the utilization of brackish and marine environments, it may be selected against in ducks breeding in fresh water, where fish competition may reduce optimal food item size. In conclusion, salinity is an important habitat barrier in both breeding and overwintering diving ducks, but there are various ways of crossing this barrier. To understand better how ducks utilize their habitats, however, it is necessary to measure habitat salinity levels and the size of both ducks and their preferred and less-preferred food types.     

Effects of demanding foraging conditions on cache retrival accuracy in food-caching mountain chickadees (Poecile gambeli)

Birds rely, at least in part, on spatial memory for recovering previously hidden caches but accurate cache recovery may be more critical for birds that forage in harsh conditions where the food supply is limited and unpredictable. Failure to find caches in these conditions may potentially result in death from starvation. In order to test this hypothesis we compared the cache recovery behaviour of 24 wild-caught mountain chickadees (Poecile gambeli), half of which were maintained on a limited and unpredictable food supply while the rest were maintained on an ad libitum food supply for 60 days. We then tested their cache retrieval accuracy by allowing birds from both groups to cache seeds in the experimental room and recover them 5 hours later. Our results showed that birds maintained on a limited and unpredictable food supply made significantly fewer visits to non-cache sites when recovering their caches compared to birds maintained on ad libitum food. We found the same difference in performance in two versions of a one-trial associative learning task in which the birds had to rely on memory to find previously encountered hidden food. In a non-spatial memory version of the task, in which the baited feeder was clearly marked, there were no significant differences between the two groups. We therefore concluded that the two groups differed in their efficiency at cache retrieval. We suggest that this difference is more likely to be attributable to a difference in memory (encoding or recall) than to a difference in their motivation to search for hidden food, although the possibility of some motivational differences still exists. Overall, our results suggest that demanding foraging conditions favour more accurate cache retrieval in food-caching birds.     

The effects of operant control over food and light on the behaviour of domestic hens

In intensive farming systems, the animals have little control over important elements in their environments. For instance, food of a pre-set type is delivered at set times, and the lighting schedule is controlled by the farmer. It has been suggested that low levels of environmental control over important events may reduce welfare by increasing passivity and stress. This study aimed to evaluate the effect of providing control over food and lighting additional to a restricted regime on the behaviour of small groups of laying hens (Gallus gallus domesticus). Twelve pens, each containing five birds, were paired to give six controlling and six non-controlling pens. These pairs of pens were yoked, such that birds in the controlling pens were able to make an operant response to gain access to extra food and light, whilst the yoked pens also received these outcomes but were unable to control their occurrence. The birds were kept continuously in the experimental conditions for 9 weeks. Records were made of general behaviour and activity, aggression and plumage damage scores, every 2 weeks. Data on key-pecking and egg production were continuously recorded throughout the experiment. The controlling birds used the operant keys to open the feeder for an average of 92min and to turn on the light for 46min per pen per day. The high number of key-pecks indicates that the birds were motivated to make use of the keys to control access to additional food and light. The non-controlling treatment pens showed significantly higher levels of preening and resting. Contrary to previous studies the use of operant feeders in this experiment did not induce a high level of feather pecking or aggressive interactions, as there was no significant difference between treatments. During the experiment the non-controlling hens laid significantly more eggs than the controlling hens. The results suggest that lack of control over these particular environmental events induced mild stress in the non-controlling pens of birds, and that further investigations into the effect of lack of control on welfare would be warranted.     

Effect of anthropogenic feeding regimes on activity rhythms of laboratory mussels exposed to natural light

Anthropogenic disturbance may affect animal behaviour and should generally be minimised. We examined how anthropogenic disturbance (24 h food deprivation) affected circadian rhythms in laboratory mussels Mytilus edulis exposed to natural light in the absence of tides. Repeated measures data were collected on mussel gape angle, exhalant pumping and valve adduction using a Hall sensor system over eight consecutive 24 h periods when exposed to two feeding conditions after 24 h food deprivation. Mussels (fed once per day at either midday or midnight) exposed to natural light showed a clear day–night rhythm with increased nocturnal activity: significantly greater gape angle, increased exhalant pumping and had significantly higher valve adduction rates. However, circadian rhythms were less clear directly after anthropogenic food deprivation, in terms of the circadian rhythm in gape angle becoming significantly more apparent over the following days. Unlike mussels fed at midnight, those fed at midday displayed no significant change in gape angle from the hour before to the hour after they were fed, i.e. mussels given food at midday reacted to this food less than mussels fed at midnight. We suggest that independent of feeding time, laboratory mussels exposed to natural light and free from anthropogenic disturbance increase feeding activity at night because their circadian rhythms are strongly influenced by light levels. This study emphasises that the behaviour of animals in the laboratory and in the wild can be altered by anthropogenic disturbances such as vibrations caused by experimental setups and artificial illumination at night.     

Habitat selection and coexistence of migrants and Afrotropical residents

In this paper I discuss factors that influence the habitat choice of small migrant birds on their Afrotropical wintering grounds and the ecological isolation of migrants and residents. The main characteristic of migrants is the use of resources which are sporadic in space and time. The majority of migrants occur in seasonal savannas and open woodland, mostly using temporarily and locally abundant food sources generally unused by residents. Migrants are more eurytopic and exploit more open parts of the habitats than ecologically similar tropical species. In some guilds, the foraging speed and rate of migrants is higher and they use their wings more often in comparison to residents. There is weak evidence that niche shifts of residents are induced by the arrival of migrants. Overt interspecific interactions seem to be infrequent, except in a guild of ground-feeding birds which rely on a rather predictable but poor food supply. In this guild, residents, but not intra-African migrants, dominated Palaearctic migrants in aggressive encounters irrespective of body-size. In contrast to this, dominance was size-dependent among wintering Palaearctic migrants.     

食物因素对笼养褐马鸡冬季打斗行为的影响

绝大多数动物社群中都存在着等级行为[2 ,10 ] ,高等级个体在取食、交配等方面都拥有优先权 ,最终导致高等级个体具有更高的存活率和繁殖率[1,3 ,4 ,7～ 9] 。这种等级行为可以避免频繁的打斗所带来的伤害和能量消耗。但是当争夺的资源很重要时 ,低等级个体将会忍受一定程度的代价以打斗的方式去争夺资源[6] 。有关食物分布格局和饥饿状况对鸟类取食打斗行为的影响几乎还为未见报道 ,本文利用冬季集群期内的一个笼养褐马鸡(Ｃｒｏｓｓｏｐｔｉｌｏｎｍａｎｔｃｈｕｒｉｃｕｍ )人工种群 ,研究了不同食物分布格局和饥饿状况下取食和打斗行为…     

Characteristic base sequence patterns of promoter and terminator sites in phi X174 and fd phage DNAs

An overall theory for the evolution of complexity in passerine broadcast song is advanced based on the proposition that new birds should attempt to match the songs of residents. We assume that social systems result from competition between individuals for resources. Individuals which by aggressive interaction have attained some priority of access to a resource (territory, food, or mate) should advertise this. New birds singing in an area will reveal their non-residential status by their song and hence will announce an assymmetry in competition that favours the residents because of their prior knowledge. Thus new birds should learn to match in order to reduce this asymmetry. Counter-selection on residents to reduce the incidence of matching should favour the evolution of song complexity. The degree of complexity should vary directly with the degree of competition. Predictions from these assumptions are advanced.     

Evidence of cannibalism and bentho-pelagic coupling within the life cycle of the mussel, Perna canaliculus

The feeding ecology of the green-lipped mussel, Perna canaliculus, was investigated within three intertidal mussel beds along Ninety Mile Beach, northern New Zealand, between August 2000 and March 2001. Adult mussels of different sizes (45-105 mm in shell length) were collected from the intertidal sites about 30 min after being submerged by the incoming tide for gut content analyses. Results of these analyses indicate that mussels consume a variety of phytoplankton, micro- and mesozooplankton, including mussel larvae and post-larvae. Cannibalism of juveniles of up to 620 μm was recorded for intertidal mussels, and conspecifics of up to 2.4 mm were found within the stomachs of additional mussels collected in August 2000 from a nearby subtidal site. For all three intertidal populations, mussel larvae and juveniles contribute about 70% of the food particle consumption during the spawning peak in August, while phytoplankton and other zooplankton constitute the majority of the food source (about 99%) in March, during gametogenesis. Larger intertidal mussels tended to have more food particles in their stomachs than smaller mussels within all three populations. Distinctive differences in food consumption among intertidal populations directly coincide with variations in total particulate matter (TPM), particulate organic matter (POM) and percent organic matter (OM) in the adjacent seawater.Separate experiments designed to test the feeding behavior of mussels feeding at different times during the incoming tide were conducted at one of the intertidal sites during August 2000 and March 2001. Results from these experiments indicate a marked shift in food consumption from bivalves to other mesozooplankton in August, and from phytoplankton to mesozooplankton in March. The observed combination of mussel predatory and grazing behavior over the incoming tide and through the year provides evidence for a strong food-web link between the benthic and pelagic life stages of this species. Furthermore, the high rate of cannibalism during some months of the year suggests that this source of food may significantly contribute to the energy budget of wild populations, with potential implications for evolutionary adaptive success.     

Claw removal and feeding ability in the edible crab,Cancer pagurus: Implications for fishery practice

Feeding ability and motivation were assessed in the edible crab, Cancer pagurus, to investigate how the fishery practice of de-clawing may affect live crabs returned to the sea. Crabs were either induced to autotomise one claw, or were only handled, before they were offered food. Initially, autotomised and handled crabs were offered mussels, Mytilis edulis, a large part of their natural diet. After 3 days, both autotomised and handled crabs were then offered fish, a more readily handled food source. Autotomy induced crabs consumed significantly fewer mussels and less mussel mass, but ate significantly more mass of fish. This indicates that the effect of autotomy was a reduction of ability to feed on mussels rather than a general reduction of feeding motivation. The discontinuation of claw removal needs to be considered, both for the sustainability of the fishery and animal welfare concerns.