Ronald C. Ydenberg

Neighbours, strangers, and the asymmetric war of attrition

Abstract The literature showing that territorial residents generally respond more intensely to an intrusion by a stranger than by a known neighbour is reviewed. The functional basis of this discrimination has not been seriously considered in this extensive literature, and it is shown here how the asymmetric war of attrition can explain why neighbours settle with relatively little aggression. In the asymmetric war-of-attrition model the degree of escalation observed in a territorial contest depends on the familiarity of the contestants with each other. Predictions of this model about neighbour-stranger contests are supported by data in the literature.

Begging and provisioning in broods of asynchronously-hatched yellow-headed blackbird nestlings

Studies of begging have found a positive relationship between begging level and provisioning level. Studies of unequal nestlings, however, have found that small nestlings generally beg more but are fed less than their larger siblings. We manipulated the begging levels of yellow-headed blackbird (Xanthocephalus xanthocephalus) chicks to investigate how begging benefits individuals in broods of unequal siblings. Food-deprived chicks begged more and were fed more; satiated chicks begged less and were fed less. When we deprived each chick of a brood in turn, large and small chicks generally increased begging and received more provisioning. Small chicks, however, rarely received more food than their larger siblings even when they behged relatively more. Parent yellow-headed blackbirds increase provisioning to hungry begging chicks, but also allocate food based on relative offspring size.

Begging tactics of nestling yellow-headed blackbirds,Xanthocephalus xanthocephalus, in relation to need

Abstract Theoretical models suggest that begging may signal nestling need. ‘Need’ for food can be either short term (hunger) or long term (amount of food required to fledge, which may be influenced by body condition, sex or rank in the brood). Studies have shown that begging carries information about short-term need, but have not provided evidence that begging can carry information about long-term need. Signals of long-term need may be unstable if larger chicks out-compete their needier siblings. This study investigated whether nestling yellow-headed blackbirds beg according to long-term need in field and laboratory experiments. In yellow-headed blackbirds, smaller nestlings, males and chicks in poor condition should value food more highly. When hunger level was controlled, males and chicks in poor condition begged more than females and chicks in good condition, respectively, and chicks begged more when paired with larger rather than smaller nestmates. In yellow-headed blackbirds, even when nestmates have unequal competitive abilities, begging can carry information about nestling long-term need for food. 1996 The Association for the Study of Animal Behaviour

Aerobiosis and anaerobiosis during diving by western grebes: an optimal foraging approach

It is widely assumed that anaerobic diving is inefficient, and yet anaerobic dives are regularly observed in nature. We develop a model of diving, using a dynamic programming approach, that assumes dives are made to capture food. The essence of the model is that while aerobic diving is energetically efficient (in terms of glucose expended per mol of ATP produced), it allows only brief underwater excursions. Anaerobic diving is much less efficient, but allows for longer dives, at the eventual expense of a long, enforced recovery period on the surface. We show how these costs and benefits interact, and that anaerobic diving is profitable under some circumstances. In particular, anaerobic diving is favored when prey occur in dense, mobile and hard-to-find concentrations, because it allows fuller exploitation of the concentration before it escapes or disappears. The model also provides a working hypothesis for the patterning of behavior observed in the field.

Western sandpipers have altered migration tactics as peregrine falcon populations have recovered

The presence of top predators can affect prey behaviour, morphology and life history, and thereby can produce indirect population consequences greater and further reaching than direct depredation would have alone. Raptor species in the Americas are recovering since restrictions on the use of dichlorodiphenyltrichloroethane (DDT) and the implementation of conservation measures, in effect constituting a hemisphere–wide predator–reintroduction experiment, and profound effects on populations of their prey are to be expected. Here, we document changes in the behaviour of western sandpipers (Calidris mauri) at migratory stopover sites over two decades. Since 1985, migratory body mass and stopover durations of western sandpipers have fallen steadily at some stopovers in the Strait of Georgia, British Columbia. Comparisons between years, sites and seasons strongly implicate increasing danger from the recovery of peregrine falcons (Falco peregrinus) as a causal factor. A decade–long ongoing steep decline in sandpiper numbers censused on our study site is explained entirely by the shortening stopover duration, rather than fewer individuals using the site. Such behavioural changes are probably general among migratory shorebird species, and may be contributing to the widespread census declines reported in North America.

The effect of personality on social foraging: shy barnacle geese scrounge more

Animals foraging in groups can either search for food themselves (producing) or search for the food discoveries of other individuals (scrounging). Tactic use in producer–scrounger games is partly flexible but individuals tend to show consistency in tactic use under different conditions suggesting that personality might play a role in tactic use in producer–scrounger games. Here we studied the use of producing and scrounging tactics by bold and shy barnacle geese (Branta leucopsis), where boldness is a personality trait known to be repeatable over time in this species. We defined individuals as bold, shy or intermediate based on two novel object tests. We scored the frequency of finding food patches (the outcome of investing in producing) and joining patches (the outcome of investing in scrounging) by bold and shy individuals and their feeding time. Shy individuals had a higher frequency of joining than bold individuals, demonstrating for the first time that personality is associated with tactic use in a producer–scrounger game. Bold individuals tended to spend more time feeding than shy individuals. Our results highlight the importance of including individual behavioural variation in models of producer–scrounger games.

Nomadic predators and geographical synchrony in microtine population cycles

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The role of energy intake rate in prey and habitat selection of common eiders Somateria mollissima in winter : a risk-sensitive interpretation

We measured prey selection and habitat profitability of common eiders Somateria mollissima L. wintering in the Gulf of St. Lawrence, Quebec, Canada. Prey selection was evaluated by comparing the frequency of prey in stomachs of shot eiders with their frequency in the sublittoral zone. Habitat profitability was estimated using information on time spent feeding, foraging success, diving durations and energy content of the prey. In this region, eiders forage on a variety of prey types from several distinct habitats, kelp beds, urchin barrens and beds of the phaeophyte Agarum cribrosum (Mert.)

The effects of wing loading and gender on the escape flights of least sandpipers (Calidris minutilla) and western sandpipers (Calidris mauri)

Abstract. High body mass caused by fat storage during migration is believed to increase a birds risk of predation by decreasing its ability to escape predators. We demonstrate the negative effect of wing loading (mass/wing area) on escape speed and angle of two migrating species of shorebird. We also show significant differences in escape performance between the species and genders. To help explain these differences, we test two potential proximate causes, wing shape and leg bone length. Wing shape is correlated with differences in escape performance between the species, but we found no correlation of wing shape or leg bone length with gender. Ultimately, greater predation risk due to habitat use or larger body size, for the species and genders respectively, may have resulted in evolution of enhanced escape ability.

Personality predicts the use of social information

The use of social information is known to affect various important aspects of an individuals ecology, such as foraging, dispersal and space use and is generally assumed to be entirely flexible and context dependent. However, the potential link between personality differences and social information use has received little attention. In this study, we studied whether use of social information was related to personality, using barnacle geese, Branta leucopsis, where boldness is a personality trait known to be consistent over time. We found that the use of social information decreased with increasing boldness score of the individuals. Individuals had lower feeding times when they did not follow the social information and this effect was unrelated to boldness score. When manipulating social information, thereby making it incorrect, individuals irrespective of their boldness score, learned that it was incorrect and ignored it. Our results show that social information use depends on the personality type of an individual, which calls for incorporation of these personality-related differences in studies of spatial distribution of animals in which social information use plays a role.