Characteristics and Consequences of Nest-Site Fidelity in Wood Ducks

Abstract

-We used nine years of nesting data from a population of Wood Ducks (Aix sponsa) using nest boxes to test predictions regarding proximate controls of nest-site fidelity and the consequences of returning to the same nest site. Overall, 41.9% of females returned to the same nest box in year t + 1, 37.5% nested in a different box on the same wetland, and 20.5% of females moved to a different wetland to nest. There were no yearly differences in the degree of nest-site fidelity, and females using different wetlands between years travelled a median of two wetlands and moved an average distance of 1.3 km. Females nesting successfully used the same nest box to a greater extent in year t + 1 than females that were not successful. The positive association between nest success and nest-site fidelity also occurred within breeding seasons. Degree of nest-site fidelity exhibited by females was similar within and between breeding seasons. After controlling for variation in nest success, nest-site fidelity of yearlings did not differ from that of adults. Proportion of females returning to the same box in year t + 1 was not correlated with estimated population size of breeding females in that year. Females returning to the same box nested earlier than females using different boxes, but clutch size did not differ. Overall, females nesting in the same box did not have greater nest success in year t + 1, were not more likely to have nests parasitized, and did not survive better to year t + 2 than females nesting in different boxes. However, females that nested unsuccessfully tended to improve nest success by moving to a different nest box. Received 1 August 1991, accepted 18 February 1992. MANY SPECIES of migratory birds show a high degree of fidelity to previous breeding sites both within and between seasons (Greenwood and Harvey 1982). Males of most species have greater breeding-site fidelity than do females (Greenwood 1980). In waterfowl, however, female-biased natal philopatry and nest-site fidelity is the rule (Rohwer and Anderson 1988). Pair bonds are formed on winter areas or during spring migration, and the pair returns to the female's natal area or previous nesting location (Dow and Fredga 1983, Hepp et al. 1989, Gauthier 1990). Widespread occurrence of breeding-site fidelity in birds suggests that the behavior is beneficial. Familiarity with an area may increase foraging efficiency, predator avoidance, dominance status, and the likelihood of pairing with a familiar partner, all of which may enhance reproductive success (Greenwood and Harvey 1982). Common Goldeneyes (Bucephala clangula), for example, that changed nest boxes nested later, produced smaller clutches, and had lower nesting success than females that did not change nest sites (Dow and Fredga 1983). Female Willow Ptarmigans (Lagopus lagopus) pairing with previous mates nested earlier and produced heavier chicks than females that switched partners (Schieck and Hannon 1989). The decision to return to a previous breeding site may involve several factors. Competition for nest sites may influence whether individuals return and may be especially important in cavity-nesting species (Dow and Fredga 1983). Previous experience is another factor influencing nest-site fidelity in birds. Individuals nesting successfully are more likely to return to the same nest site than individuals that are not successful (Gavin and Bollinger 1988, Gauthier 1990, Beletsky and Orians 1991; but see Haig and Oring 1988). Site quality may interact with nest success to influence subsequent nesting decisions (Weatherhead and Boak 1986, Bollinger and Gavin 1989). Nest-site fidelity also may be influenced by age, with yearlings having a greater probability of changing nest sites than adults (Newton and Marquiss 1982). Causes for age-specific differences in fidelity are unclear (Greenwood and Harvey 1982). It is possible that young individuals use poor-quality sites during initial nest attempts and move to betterquality sites when these sites become available.