FACTORS ASSOCIATED WITH GROWTH OF NESTLING PROTHONOTARY WARBLERS

Abstract

The Prothonotary Warbler (Protonotaria citrea) is the only wood warbler in the eastern United States that nests in cavities. It readily accepts nest boxes in lieu of natural breeding sites and therefore provides an excellent model for tests of ecological factors associated with reproductive success. During 1987, 300 nest boxes were placed along a 30-km transect along the tidal James River in eastern Virginia, and these nest boxes have been monitored every year through 2000. During the 1999 and 2000 breeding seasons, we collected 2910 measurements of nestling mass, and recorded ages of parental females, dates of clutch initiation and hatching, brood sizes, and the number of young that survived to fledging. Multivariate analysis of variance indicates that nestling mass was a significant function of brood size, hatching date, age of the female, and year, even when the effects of all independent variables were considered simultaneously. Growth rate and fledging mass were significantly lower in larger broods. Two- to three-year-old females fledged nestlings with greater mass than one-year-old females and females older than three years. Frequency of handling nestlings was not significantly associated with changes in their mass. Ambient temperature of the study area during the breeding season was significantly colder during 1999 than during 2000. Growth rate, fledging mass, and rate of survival of nestlings to fledging were lower during 1999 than during 2000. Growth of nestling birds was related to a large suite of intrinsic variables, but application of growth data to environmental concerns requires knowledge of both demographic and ecological factors.