Changes in Reproductive Function of Free-Living Birds in Direct Response to Environmental Perturbations

Abstract

There is a general concensus of opinion that onset of breeding in birds occurs when trophic resources are favorable for production and survival of young (e.g., Lack 1968, Perrins 1970). The environmental factors that provide proximate cues for development of reproductive function and timing of the onset of breeding have received considerable attention over the past 50 years (e.g., Farner and Gwinner 1980, Farner 1985, Wingfield 1980, 1983). However, the hormonal mechanisms underlying development of the gonads and associated structures, onset of breeding, transitions from sexual to parental behavior, and repetition of this temporal pattern in multiple broods have, of necessity, assumed ideal environmental conditions. Such an approach is crucial if experimental paradigms are to be controlled adequately and the mechanisms investigated. Nevertheless, free-living birds rarely experience “ ideal” conditions for prolonged periods and are exposed to a variety of unfavorable environmental factors that have profound influences on reproductive success. Thus one can pose a question, “what happens when something goes awry?”. For example, predators may consume the eggs or young, or storms may reduce food resources (Whitmore et al. 1977, Ojanen 1979, Pullamen 1977, Tompa 1971).