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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