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Glucocorticoids (GC) and triiodothyronine (T3) are two endocrine markers commonly used to quantify resource limitation, yet the relationships between these markers and the energetic state of animals has been studied primarily in small-bodied species in captivity. Free-ranging animals, however, adjust energy intake in accordance with their energy reserves, a behavior known as state-dependent foraging. Further, links between life-history strategies and metabolic allometries cause energy intake and energy reserves to be more strongly coupled in small animals relative to large animals. Because GC and T3 may reflect energy intake or energy reserves, state-dependent foraging and body size may cause endocrine–energy relationships to vary among taxa and environments. To extend the utility of endocrine markers to large-bodied, free-ranging animals, we evaluated how state-dependent foraging, energy reserves, and energy intake influenced fecal GC and fecal T3 concentrations in free-ranging moose (Alces alces). Compared with individuals possessing abundant energy reserves, individuals with few energy reserves had higher energy intake and high fecal T3 concentrations, thereby supporting state-dependent foraging. Although fecal GC did not vary strongly with energy reserves, individuals with higher fecal GC tended to have fewer energy reserves and substantially greater energy intake than those with low fecal GC. Consequently, individuals with greater energy intake had both high fecal T3 and high fecal GC concentrations, a pattern inconsistent with previous documentation from captive animal studies. We posit that a positive relationship between GC and T3 may be expected in animals exhibiting state-dependent foraging if GC is associated with increased foraging and energy intake. Thus, we recommend that additional investigations of GC– and T3–energy relationships be conducted in free-ranging animals across a diversity of body size and life-history strategies before these endocrine markers are applied broadly to wildlife conservation and management.

Foraging animals have several tools for managing the risk of predation, and the foraging games between them and their predators. Among these, time allocation is foremost, followed by vigilance and apprehension. Together, their use influences a forager's time allocation and giving-up density (GUD) in depletable resource patches. We examined Allenby's gerbils (Gerbilus andersoni allenbyi) exploiting seed resource patches in a large vivarium under varying moon phases in the presence of a red fox (Vulpes vulpes). We measured time allocated to foraging patches electronically and GUDs from seeds left behind in resource patches. From these, we estimated handling times, attack rates and quitting harvest rates (QHRs). Gerbils displayed greater vigilance (lower attack rates) at brighter moon phases (full < wane < wax < new). Similarly, they displayed higher GUDs at brighter moon phases (wax > full > new > wane). Finally, gerbils displayed higher QHRs at new and waxing moon phases. Differences across moon phases not only reflect changing time allocation and vigilance, but changes in the state of the foragers and their marginal value of energy. Early in the lunar cycle, gerbils rely on vigilance and sacrifice state to avoid risk; later they defend state at the cost of increased time allocation; finally their state can recover as safe opportunities expand. In the predator–prey foraging game, foxes may contribute to these patterns of behaviours by modulating their own activity in response to the opportunities presented in each moon phase.

Prey species make choices about whether to employ costly predator avoidance behaviors throughout their growth and lifecycle. Here, we explore the effects of prey size at a given age (ontogenetic size) and prey growth on optimal behavior using a dynamic optimization model. Under the assumption that prey experience greatest predation risk at intermediate or large sizes, and that growth is fastest at intermediate or large sizes, we find that prey should generally forage when they are small in size and hide when they are larger due to a critical strategy switching size threshold. But this is dependent both on the mortality risks and on the rate of growth. Higher background mortality rates or lower predator-induced detection costs of foraging reduce the size at which prey switches from foraging to hiding. Rapid initial growth leads to decreased overall survival and a wider range of conditions under which the prey hides from the predator. As a test case, the model is parametrized with data and applied to understand differing risk-reducing behaviors between cannibal and non-cannibal Leptinotarsa decemlineata, Colorado potato beetle, larvae. The model predicts that a wide range of parameter values lead to differing behaviors of cannibals and non-cannibals of the same age due to differences in ontogenetic size. We also see that individuals with swifter early growth switch to hiding at larger sizes but will often have earlier strategy switching times. This increases survival of cannibals to the critical pupation size with the largest increases occurring when the baseline death rate is high. Our findings suggest that ecological factors that affect the rate of growth during development, even if final size is not affected, may have an important role in prey responses to predators.

Among species where there is a risk to leaving offspring unattended, parents usually take alternating shifts guarding their young. However, they may occasionally exhibit brood neglect by leaving their offspring unattended at the nest. To investigate this phenomenon further, we examined the foraging behavior of the northern gannet (Morus bassanus) during chick-rearing. This species has a prolonged nestling period (13 weeks) and the single chick is usually guarded by one or other of its parents, because unattended chicks are frequently attacked by conspecifics. We tested the prediction that the foraging behavior of adults when they left their offspring alone at the nest (unattended trips) would differ in character to when adults left offspring with their partner (attended trips). Brood neglect typically occurred after a longer-than-average attendance period at the nest. Unattended trips were, on average, about half the duration of attended trips, and therefore much closer to the colony. There was also a difference in departure direction between attended and unattended trips, with unattended trips tending to be northeast of the colony. Chicks were fed by parents after both attended and unattended trips, but the frequency and the duration of unattended trips increased as chicks grew older whereas the duration of attended trips decreased as chicks grew. These results indicate that parents may be making a trade-off between risk of attack to their offspring and food-intake rate, and that the solution to this trade-off is dependent on chick age.

Ethanol occurs in fleshy fruit as a result of sugar fermentation by both microorganisms and the plant itself; its concentration [EtOH] increases as fruit ripens. At low concentrations, ethanol is a nutrient, whereas at high concentrations, it is toxic. We hypothesized that the effects of ethanol on the foraging behavior of frugivorous vertebrates depend on its concentration in food and the body condition of the forager. We predicted that ethanol stimulates food consumption when its concentration is similar to that found in ripe fruit, whereas [EtOH] below or above that of ripe fruit has either no effect, or else deters foragers, respectively. Moreover, we expected that the amount of food ingested on a particular day of feeding influences the toxic effects of ethanol on a forager, and consequently shapes its feeding decisions on the following day. We therefore predicted that for a food-restricted forager, ethanol-rich food is of lower value than ethanol-free food. We used Egyptian fruit bats ( Rousettus aegyptiacus ) as a model to test our hypotheses, and found that ethanol did not increase the value of food for the bats. High [EtOH] reduced the value of food for well-fed bats. However, for food-restricted bats, there was no difference between the value of ethanol-rich and ethanol-free food. Thus, microorganisms, via their production of ethanol, may affect the patterns of feeding of seed-dispersing frugivores. However, these patterns could be modified by the body condition of the animals because they might trade-off the costs of intoxication against the value of nutrients acquired.

Many animals exhibit behavioural syndromes—consistent individual differences in behaviour across two or more contexts or situations. Here, we present adaptive, state-dependent mathematical models for analysing issues about behavioural syndromes. We find that asset protection (where individuals with more ‘assets’ tend be more cautious) and starvation avoidance, two state-dependent mechanisms, can explain short-term behavioural consistency, but not long-term stable behavioural types (BTs). These negative-feedback mechanisms tend to produce convergence in state and behaviour over time. In contrast, a positive-feedback mechanism, state-dependent safety (where individuals with higher energy reserves, size, condition or vigour are better at coping with predators), can explain stable differences in personality over the long term. The relative importance of negative- and positive-feedback mechanisms in governing behavioural consistency depends on environmental conditions (predation risk and resource availability). Behavioural syndromes emerge more readily in conditions of intermediate ecological favourability (e.g. medium risk and medium resources, or high risk and resources, or low risk and resources). Under these conditions, individuals with higher initial state maintain a tendency to be bolder than individuals that start with low initial state; i.e. later BT is determined by state during an early ‘developmental window’. In contrast, when conditions are highly favourable (low risk, high resources) or highly unfavourable (high risk, low resources), individuals converge to be all relatively bold or all relatively cautious, respectively. In those circumstances, initial differences in BT are not maintained over the long term, and there is no early developmental window where initial state governs later BT. The exact range of ecological conditions favouring behavioural syndromes depends also on the strength of state-dependent safety.

Summary Animals frequently exhibit consistent among‐individual differences in behavioural and physiological traits that are inherently flexible. Why should individuals differ consistently in their expression of labile traits? Recently, positive feedbacks between state and behaviour have been proposed as a possible explanation for the maintenance of consistent among‐individual differences in both state and behaviour. If state affects behaviour, and behaviour reciprocally affects state, then differences in either state or behaviour that arise among individuals even by chance could be maintained over extended periods of time. We tested for positive feedbacks experimentally using wild‐caught red knots (Calidris canutus islandica). In the wild, knots exhibit consistent among‐individual differences in digestive physiology (the mass of the muscular part of the stomach, the gizzard) and foraging behaviour (diet), two inherently labile traits. Experimentally manipulated diet quality had a large effect on gizzard mass. Experimentally manipulated gizzard mass reciprocally influenced total food eaten during ad libitum trials. The effect of gizzard mass on diet choice, though in the predicted direction, was not statistically significant. Individuals exhibited consistent differences in foraging behaviour of unknown origin independent of current gizzard mass, as well as large residual unexplained variance in foraging behaviour. These two sources of variation in foraging behaviour overruled the gizzard mass‐dependent foraging behaviour and hence eroded the treatment‐related differences in gizzard mass. We conclude that positive feedbacks between diet choice and gizzard mass play at best a limited role in maintaining among‐individual variation in gizzard mass in red knots. Furthermore, we suggest that many models of state–behaviour feedbacks likely overestimate their potential importance in maintaining long‐term among‐individual variation in labile traits because most models of state–behaviour feedbacks fail to account for the effects of additional factors that may act to disrupt the feedback loops. The among‐individual differences in diet choice observed during solitary foraging trials eroded the consistent among‐individual differences in gizzard mass observed following periods of staple diet treatments in which knots foraged in social groups. Social foraging interactions may play an important role determining the expression of foraging behaviours such as intake rate that in turn influence gizzard mass. Further studies are needed to experimentally test the role of social interactions as a mechanism generating consistent among‐individual differences in foraging behaviours and gizzard mass. A lay summary is available for this article. Lay Summary

Habitat characteristics and microhabitat of organisms pose a number of choices to foraging species, for example where and how to search for prey, which prey to select and what foraging technique to employ. Predators can enhance the profitability of foraging by adapting their strategies flexibly in relation to prey characteristics and environmental factors. To investigate the influence of rocky shore characteristics viz., condition of rock, position of limpet on the rock, stage of tide, and limpet opening technique of oystercatcher on the profitability of limpet foraging, a total of 193 attacks on limpets ( Patella spp.) by Eurasian oystercatchers ( Haematopus ostralegus ) were made on Lundy Island, UK, using focal animal sampling. Multiple regression revealed that profitability was influenced by the condition of the rock and the limpet opening technique employed by oystercatchers. The profitability of the limpet opening technique appears to be associated with the condition of the rock. Oystercatchers forage by adapting their foraging strategy in accordance with the nature of the rocks i.e. wetness on which they are foraging.

For many species, behavioral modification is an effective strategy to mitigate negative effects of harsh and unpredictable environmental conditions. When behavioral modifications are not sufficient to mitigate extreme environmental conditions, intrinsic factors may be the primary determinant of survival. We investigated how movement behavior, and internal (i.e., nutrition and age) and external (i.e., food availability and snow depth) states affect survival over winter of a long‐lived and highly faithful species (mule deer; Odocoileus hemionus). We first tested whether animals changed their behavior during winter based on internal and external states; we subsequently investigated how behavior and state interacted to influence survival in the face of extraordinary winter conditions. Movement behavior changed minimally as a function of age and nutrition; yet, movement behavior affected survival—animals that exhibited more restricted movements were more likely to succumb to mortality overwinter than animals with less restricted movements. Additionally, nutrition and cumulative snow depth had a strong effect on survival: animals that were exposed to deep snow and began winter with low fat were much less likely to survive. Behavior was an effective tool in securing survival during mild or moderate winters, but nutrition ultimately underpinned survival during harsh winters.

The behavioural sciences are home to controversies that have survived for centuries, notably about the relation between observable behaviour and theoretical constructs addressing out-of-sight processes in the agents’ brains. There is no shared definition for cognition, but the very existence of a thriving journal called Animal Cognition proves that such controversies are still live and help to (a) promote research on the complexity of processes leading to action, and (b) nudge scholars to restrict their cognitive models to those that can be falsified experimentally. Here, we illustrate some of these issues in a limited arena, focusing on the construction and expression of subjective value and choice. Using mainly work from our own laboratory, we show that valuation of alternatives is sensitive to options’ properties, to subject’s state, and to background alternatives. These factors exert their influence at the time the subject learns about individual options, rather than at choice time. We also show that valuation can be experimentally dissociated from the cognitive representation of options’ metrics and argue that experimental animals process options independently at the time of choice, without elaborated comparisons along different dimensions. The findings we report are not consistent with the hypothesis that preference is constructed at the time of choice, a prevalent view in human decision-making research. We argue that animal cognition, viewed as a research program at the crossroads of different behavioural sciences rather than as a debate about properties of mental life, is inspiring and solid, and a progressive and progressing paradigm.