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Nest-site selection and nesting success of Wood Thrushes

1998; Wilson Ornithological Society; Volume: 110; Issue: 3 Linguagem: Inglês

1938-5447

Jeffrey P. Hoover, Margaret C. Brittingham,

Animal Behavior and Reproduction

-We characterized nest sites and compared specific nest-site characteristics to nesting success for Wood Thrushes (Hylocichla mustelina) nesting in southeastern Pennsylvania in 1991. We determined if nests were placed in areas that differed from randomly selected points within a given tract of forest and compared specific nest-site characteristics for successful nests (those that produced at least one fledgling) and nests that failed because of predation. Wood Thrushes selected nest sites non-randomly within a tract of forest, and female Wood Thrushes built nests in areas that had a higher density of trees, higher canopy, higher density of shrubs, and higher average shrub height than randomly selected points. Specific nest-site characteristics had little effect on the ultimate success or failure of nests. The only specific nest-site characteristic included in a stepwise logistic regression model comparing successful and failed nesting attempts was the concealment of the nest from above and below. The average concealment of successful nests was greater than unsuccessful nests, but the model that included nest concealment did not give good fit to the data. Rather, a landscape-level feature, size of forest tract, had the greatest influence on the success and failure of nests for Wood Thrushes in this region. Received 10 Feb. 1997, accepted 20 April 1998. The Wood Thrush (Hylocichla mustelina) is a neotropical migrant that has undergone significant population declines in recent decades (Sauer et al. 1996). Poor reproductive success, particularly as a result of high rates of nest predation, has been cited as one probable cause of the decline (Robinson 1992, Roth and Johnson 1993, Hoover et al. 1995). Identification of specific habitat features associated with nest sites and nesting success, and a calculation of the probability of success given certain characteristics are needed in order to develop long-term strategies for reversing declines in populations of Wood Thrushes and other neotropical migrants (Martin 1992). Also, information on nest-site selection may be applied to management of habitat for this and other species of neotropical migrants. General characteristics of the forest habitat where Wood Thrushes are found during the breeding season have been described by other researchers (Bertin 1977, James et al. 1984, Roth 1987). In addition, other researchers have documented the influence of landscape features such as forest patch size and proximity to edge habitat on the probability of nest success (e.g., Robinson 1988, 1992; Hoover et al. 1995). In this study, we looked at nestsite selection by Wood Thrushes in two different ways. We first determrined whether or not Wood Thrushes, within the forest, used particular areas for nesting based on the structure of the vegetation. We then measured microhabitat characteristics of successful nests and nests that were lost to predators. Our specific objectives were to: (1) determine the characteristics of the vegetation that influenced the probability that a site would be used for nesting by a Wood Thrush, and (2) determine whether or not microhabitat characteristics at the nest site influenced the probability of nesting success.