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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The behaviours of eastern chipmunks (Tamias striatus) in response to aerial predators were studied in the field using trained kestrels (Falco sparverius) flying over a food patch where animals of known gender, age and burrow location categories were foraging. Their typical response was to flee toward a nearby refuge while producing a trill. After a few seconds, chipmunks usually emerged and started to produce long (but sometimes interrupted) series of chucks while facing the predator. Acoustical analysis showed that the trill consisted of a rapid series of usually high pitched and variable notes while most chucks consisted of two partially overlapping components differing mainly in frequency range. No differences were observed between individuals of different categories for most antipredator responses. Various observations suggest that the trill functions to startle the predator and that the chuck deters the predator from hunting in the area.

Chipmunk antipredator calls were examined during the summers of 1990 and 1991. The structural characteristics of the three calls, chipping, chucking and the trill, were obtained through taped recordings and sonagraphic analysis. Behavioural observations indicated that chucking by choruses of individuals occurs in the presence of aerial predators, chipping by choruses of individuals occurs in the presence of terrestrial predators and the trill is given by single individuals when fleeing from predators. / Experiments were carried out to determine the function of the trill and chipping. Demographic and contextual effects indicate that the trill is in part a call which functions to warn kin but may also indicate to conspecifics that the caller has escaped into a refuge. An experiment with a tethered cat concluded that chipping is likely to function to deter predators from hunting in the area. This is done through vocal mobbing by several individuals whose home ranges overlap.

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