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Little theoretical or empirical research has examined how an animal that has found and exploited a new patch should determine whether and when it will renew. A rapid series of visits to the patch should provide information concerning the probability of a quick renewal. If a renewal is not encountered, however, a subsequent decrease in the rate of visits should allow monitoring of the patch at minimal cost. After a long period without renewal, a patch should not be visited at all. By analogy with area-concentrated search, I propose the term 'time-concentrated sampling' (TCS) for this pattern of visits and suggest that it should be widespread for species foraging on patchy prey in environments where the probability of renewal and latency to renewal of patches are variable between patches. In this study, I tested whether eastern chipmunks (Tamias striatus) presented with a small number of peanuts followed by a small patch of sunflower seeds exhibit TCS following their depletion of these and, if so, whether their patterns of visits are influenced by potential indicators of patch value. (Abstract shortened by UMI.)

In a variable environment, the ability to track food resources that vary in time and space may increase the foraging efficiency of individuals. Tracking can be accomplished by repeatedly visiting patches, but this sampling will be economical only if its benefits outweigh its costs. I examined the effects of patch characteristics and social factors on sampling using simulation models and both large- and small-scale field experiments on eastern chipmunks ( Tamias striatus). In the first experiment, chipmunks discovered large renewing patches within a few days, sampled them frequently enough to detect most renewals, and then decreased their sampling effort after renewal ceased, showing that they can track patches over both long and short time scales. Sampling rate was higher for animals that lived near the patch, for animals that were more aggressive while in the patch, and when the number of other animals that sampled was high, but was unaffected by the quantity and frequency of renewal. I developed a model, which predicts that the optimal sampling frequency should increase with the frequency and duration of renewal and with the rate of gain in the patch, and decrease with the duration of each sampling trip. An extension of this model predicts that conspecifics will affect even non-group foragers, by competing for food and providing social information. A second field experiment showed that chipmunks decreased their sampling in response to higher competition. Although chipmunks used social information to discover a patch, there was no indication that social information caused a decrease in sampling. In conclusion, sampling to keep track of varying patches is an important component of the foraging behaviour of chipmunks. Optimal sampling behaviour is affected by patch characteristics and sampling rate will depend on (i) the ease with which animals can estimate these characteristics, (ii) the level of competition, which can alter the patch valu

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Small endotherms typically have elevated and relatively invariant rates of metabolism, but adaptations such as food hoarding and hibernation endow some species with considerable energetic flexibility in responding to resource fluctuations. I examined the interactions between resource availability, food hoarding, and hibernation in a population of eastern chipmunks (Tamias striatus) subjected to seasonal and multi-annual periods of resource shortage. Incompatibility of torpor and digestion could be an important constraint associated with relying on stored food rather than body fat during hibernation, but documentation of torpor patterns and digestive efficiency of captive chipmunks revealed that digestion is actually enhanced by torpor expression. Measures of energy expenditure and food delivery by free-ranging chipmunks in autumn revealed that food hoarding also permitted rapid accumulation of large energy reserves before thermoregulatory constraints necessitated termination of above-ground activity. Thus, a combination of food hoarding and hibernation permits rapid energy accumulation when resources are abundant and effective energy conservation when resources are scarce. Despite this, chipmunks responded to experimental increases of autumn hoard size by substantially reducing winter torpor expression, suggesting that much of the resource accumulation permitted by larder hoarding is allocated to maintaining elevated rates of metabolism in the winter hibernaculum. This pattern of allocation suggests torpor expression is associated with important costs and contradicts a major paradigm of hibernation research by demonstrating that low levels of torpor expression can reflect an absence of energetic necessity rather than a lack of physiological capability. In an ecological context, the capacity of chipmunks to vary expenditure according to resource abundance represents a potent decoupling mechanism in consumer-resource interactions. Energetic flexibility of this form

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