Wesley W. Weathers - US grants

In this collaborative research project, a behavioral ecologist (K. A. Sullivan) and a physiological ecologist (W. W. Weathers) examine the relationship between foraging efficiency, social dominance, and survivorship in a small passerine bird. the yellow-eyed junco (Junco phaenotus). The study focuses on juvenile birds during the two-week period following the termination of adult care. During this period, juvenile mortality is high (42%) and body mass is a significant predictor of survival. The period of intense selection provides an opportunity to determine whether foraging efficiency and/or social dominance also affect survivorship, and hence fitness, as predicted by current theory. The study will provide insights concerning such diverse topics as how juvenile foraging efficiency affects the length of parental care, the energy costs and benefits of social dominance, the effect of microhabitat selection on daily energy expenditure, and population regulation by juvenile survivorship.

The feeding ecology and energetics of two common surface-nesting petrels that breed in the high Antarctic, the Cape Pigeon and the Snow Petrel will be addressed through a variety of field and laboratory techniques. Both the diet and energy requirements of adults and their offspring will be quantified. By conducting measurements over three consecutive breeding seasons, interannual variation in feeding ecology and reproductive performance will be assessed. The field metabolic rate of adult petrels will be determined during the incubation and chick-rearing stages of the breeding cycle using the doubly labeled water technique. Basal metabolic rates of adults will be determined from laboratory measurements of oxygen consumption and their reproductive effort expressed as the ratio of field metabolic rate to basal metabolism. Foraging trip length of adults will be partitioned into time spent resting on water and in flight and foraging energy cost will be estimated. Nestling growth will be assessed from measurements of body mass, size and composition as functions of nestling age and nestling energy budgets will be constructed. Diet of nestlings and their parents will be determined from parental food deliveries and stable isotope analysis of prey and feces. Diet information combined with doubly labeled water measurements will allow calculation of rates of food consumption, and, hence, the trophic impact of these breeding fulmarine petrels on the surrounding marine ecosystem.

9520846 Many bird species that feed their young in the nest lay eggs that hatch asynchronously, with the first laid eggs hatching from two days to two weeks before the last laid eggs. This study tests two long-standing hypotheses that seek to explain this phenomenon. The first suggests that asynchrony increases males' contribution to reproduction and thus reproductive success of a pair, by prolonging the time that males feed females and young. The second suggests that asynchrony reduces peak energy demands, by spreading the cost of raising offspring over a longer time. Although these hypotheses differ in their details, both assume that hatching asynchrony evolved in response to food limitation during the breeding season and that it functions to reduce parental effort. Falsifying these hypotheses would mean that breeding is not invariably constrained by food availability, which would alter our understanding of the factors that limit avian reproductive success. This research will test these hypotheses by measuring the metabolic rate of free-living green-rumped parrotlets that are rearing either synchronous and asynchronous broods containing either 4 or 8 chicks. Green-rumped parrotlets exhibit the most extreme degree of hatching asynchrony found in birds, yet are capable of rearing synchronous and asynchronous broods with equal success, making them ideal subjects for this project. Field metabolic rate of parents feeding young will be determined using the doubly labeled water technique, a method that employs isotopically labeled water to determine directly metabolism of free-living animals. The results will increase our understanding of the way that costs of reproduction affect breeding systems, and the extent to which energy demands have played a role in the evolution of avian life histories. It will also expand our knowledge of tropical parrots, on e of the most threatened groups of birds, and provide baseline data that may aid future conservation efforts.