Prospecting for Nest Sites by Cavity-Nesting Ducks of the Genus Bucephala

Abstract

We studied the pattern of post-laying visitation of sites by non-nesting females in three species of cavity-nesting ducks, the Common and Barrow's goldeneyes (Bucephala clangula and B. islandica) and the Bufflehead (B. albeola). Nests were visited from mid-June to mid-July when most nesting females either had hatched their clutches or were finishing incubation. Females often visited more than one site and each site could be visited by several birds. Observations of marked individuals and body measurements of trapped birds show that most visiting females were either yearlings or failed breeders. These females always visited sites in intraor inter-specific groups, and exhibited typical vocalizations and flight patterns. We propose that these females were for sites in preparation for the next breeding season. We could not find any detrimental effects of prospecting on incubating females. We also discuss the evolutionary significance of prospecting behavior and its relationship to delayed maturity and nest-site availability for both cavityand groundnesting North American ducks. Selection of an appropriate site has an important influence on breeding success in waterfowl. In ground-nesting ducks, success and predation rates on nests have been related to both the location and the type of cover near the (Schrank 1972, Lokemoen et al. 1984). In cavity-nesting ducks, competition for sites can be intense (e.g., Jones and Leopold 1967), and nest-site location has been shown to influence reproductive success in the Common Goldeneye (Bucephala clangula; Dow and Fredga 1983). Although much quantitative information is available on nest-site characteristics for many species of ducks (e.g., Bengston 1972, Lokemoen et al. 1984), little is known about the behavioral mechanisms used in nestsite selection. Most ducks search for sites immediately before nesting (Bengston 1972, Bellrose 1976, Palmer 1976). In the genus Bucephala, however, females have been reported to search for sites at the of the summer, presumably in preparation for the next breeding (Grenquist 1963, Bengston 1966, M. Jackson in Bellrose 1976, Cramp and Simmons 1977). This behavior has often been called nest prospecting, to distinguish it from the more usual form of searching at the beginning of the breeding season. The unusual timing of searching in Bucephala is interesting for three reasons. First, all three species of Bucephala in tree cavities, and sites are often limited (Erskine 1972, Savard 1982). It is possible that searching in advance of the next breeding has evolved in response to the scarcity of suitable sites. Second, despite the above reports of end of the season searching in Bucephala, few data are available. We know of only one detailed study of searching in a hole-nesting duck (Patterson and Makepeace 1979, Patterson 1982, for the Common Shelduck, Tadorna tadorna). Third, Grenquist (1963) suggested that searching by female goldeneyes at the of the breeding might cause desertion by incubating females. This potential cost to incubating females has received little attention in previous studies. The objectives of our study were, therefore: (1) to quantify and compare the late visitation patterns of three species of cavity-nesting ducks, the Common and Barrow's goldeneyes (Bucephala islandica) and the Bufflehead (B. albeola), (2) to consider the hypothesis that females were for sites for the following year, and (3) to examine potential costs of this activity to both incubating and visiting females.