Graduate Thesis Or Dissertation


Life history and environmental influences on avian incubation and parental care in songbirds Public Deposited

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  • Patterns of nest attendance behavior by breeding birds represent a parent-offspring trade-off in which adults balance self-maintenance with parental care decisions. Incubation, in particular, is of interest because adults must provide an environment suitable for embryonic development through nest-building and contact-incubation. We evaluated how adult incubation constancy and nest visitation rates varied with life and natural history traits of temperate and tropical bird species. We found that constancy did not differ by latitude or with nest survival rate. A strong negative correlation between incubation constancy and egg mass relative to adult body mass was present. Birds with low constancy tended to have larger relative egg masses and higher basal metabolic rate. Because adult incubation constancy is relatively plastic (i.e., varies with ambient temperature), birds with larger relative eggs may respond to lower cooling rates rather than direct selection for higher or lower constancy. We then assessed if rates of nest visitation (trips to nests by adults during incubation and nestling phases) followed the predictions of the Skutch hypothesis. Skutch suggested that birds nesting in environments with high levels of nest predation would reduce numbers of trips to their nests so as to minimize the risk of visual detection by nest predators. We found support for the basic pattern predicted by Skutch. We also extended his hypothesis to predict other behavior associated with nesting, such as responses of parents to intruders at the nest. Despite apparently early departure from the nest site, adults with higher visitation rates remained conspicuous around the nest site. Thus, while the flight initiation distance from the human observer was earlier than expected, conspicuousness of behavior was associated with nest visitation rate. Finally, we assessed how an environmental variable, photoperiod, might influence rate of embryonic development in a wild songbird, Sylvia atricapilla. We exposed eggs throughout the incubation period to daily photoperiods consisting of 4 hours of light and 20 hours of dark (4L), 12 hours light and 12 hours dark (12L), 20 hours light and 4 hours dark (20L) and a skeleton photoperiod with two 1-hour pulses of light that framed a 20-hour day. We found that the skeleton treatment group differed significantly from our 4L and 12L, but not the 20L treatment groups. The skeleton photoperiod accelerated embryonic development. We suggest that photoperiod may influence incubation period in wild birds and could account for some portion of the widely observed latitudinal variation in incubation period of songbirds. We encourage others to assess how photoperiod interacts with parental attendance patterns to affect embryonic development.
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