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The storing of food is a common behaviour in the American kestrel ( Falco sparverius), a small, cavity-nesting falcon whose prey is comprised mainly of insects and small mammals. It may be a mechanism by which breeding birds ensure a sufficient food supply crucial to reproductive success. / In 1996, caching behaviour of 10 single females, 10 single males and 20 paired captive American kestrels was recorded over the breeding season at the Avian Science and Conservation Centre of McGill University. / Cache site preference and seasonal influence on caching frequencies were studied in 8 hand-raised, male kestrels in summer, fall and winter from 1996--1997. Caching frequency during the three seasons was significantly different with most occurring in fall, fewer in winter, and still fewer in summer. / Memory for locations of cached prey was tested in 7 hand-raised males, three days after a caching event, from July to September 1997. The birds located their own caches significantly better than those caches placed by the experimenter. (Abstract shortened by UMI.)

The American kestrel (Falco sparverius) - Trichinella pseudospiralis host-parasite association was used as a model to study the effect of infection on (1) mate choice of female kestrels and (2) competitive abilities of male kestrels. In 34 choice tests, female selection of infected or uninfected males was random. Male competitive abilities was assessed by observing interactions between infected and uninfected individuals in a pen with a caged female and a single nest box. In 8 of 11 trials, uninfected males spent more time in the section closest to the female than their infected rivals, and performed more chases, attacks, and displacements than the latter. These results suggest that variation in male quality is determined in part by resistance to parasitism and can affect competition for nesting territories. Females may not have evolved mechanisms to detect parasitized males because these males are unlikely to outcompete uninfected males when territories are in limited supply.

This study investigated the predatory behaviour of kestrels on insect prey in a modified open-field arena, and assessed the effects of T. pseudospiralis infections on the sequence of predatory behaviours, hunting efficiency and choice of hunting method of the birds. Choice of hunting method in kestrels was related to their appraise energy expenditure and relative success. Hunting from a perch was more common, presumably less strenuous and more successful than hunting afoot. Hunting prey confined to the vertical walls of the arena was considered more strenuous and was less successful than hunting freely-roaming ground prey. Infection with T. pseudospiralis did not affect attack rate or hunting success but altered the manner in which prey were taken. Thus, the frequency of strikes performed in level flight declined, and birds tended to hunt more on foot. In flight, the frequency of wing beats and the horizontal distance travelled to regain the elevated perch increased. Concordance was found between intensity of infection and magnitude of change in body weight and flight activities. (Abstract shortened by UMI.)

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This project investigated postnatal development of the adrenocortical function in captive American kestrels (Falco sparverius) employing measurements of basal and stress-induced levels of corticosterone at specific developmental stages. Chicks aged 10-days exhibited partially functioning adrenocortical systems with baseline levels comparable to adults. The ability to respond to external stressors increased through postnatal development and by the age of 22 days, stress-induced maximal levels of corticosterone were indistinguishable from those of one-year old adults, and levels of 28-day old birds were significantly higher than these adults. In addition, baseline and maximum stress-induced levels of corticosterone at all ages were significantly higher in first-hatched chicks than all other siblings and these effects grew stronger through development. These results suggest that the brain-pituitary-adrenal axis in this semi-altricial species is (1) already partially developed in young chicks and (2) only becomes fully functional when behavioral and neuromuscular development is nearly complete. Furthermore, results from this study suggest that hatching asynchrony has an effect on this variation in stress-induced maximal levels of corticosterone during the latter half of postnatal development, with a higher degree of hatching asynchrony leading to larger disparity in adrenocortical function between first- and fourth-hatched chicks. This adrenocortical disparity resulting from female-mediated hatching asynchrony may potentially lead to both brood-reduction and brood survival under diametric food conditions, ensuring that the female's reproductive fitness is maximized in varying habitats. Variation of adrenocortical function among siblings may increase female efficiency in raising a brood of fit chicks, maximizing her reproductive success.

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