Nesting success and nest-site selection by a neotropical migrant in a fragmented landscape

Abstract

Information on breeding-habitat requirements for neotropical migrants is important for managing remnant woodlots used by these species. In 1998, we examined nest-site selection and nesting success of hooded warblers (Wilsonia citrina) in seven woodlots of the highly fragmented Carolinian Forest in southwestern Ontario, Canada. We sampled and compared 23 nest and unoccupied sites. We recorded number of eggs, number of nestlings, and number of young fledged, as measures of productivity, and the presence of cowbird (Molothrus ater) parasitism. Nest sites had an overall higher percentage of vegetation cover than unoccupied sites (U [Formula: see text] 75.0, P < 0.04) and a lower basal area of trees with a diameter at breast height between 7.5 and 15 cm (U = 376.0, P = 0.014). Our best logistic regression model showed that the probability of a site being occupied by nesting hooded warblers increased with the height of the subcanopy and with the percentage of vegetation cover at the 1- to 2-m height interval. The model correctly classified 74.6% of the nest and unoccupied sites. Nest survivorship for the entire nesting period was estimated at 67.1%. Cowbird parasitism was low (18%). No nest-site characteristics were correlated with any of the productivity parameters (rs[Formula: see text] 0.663, P [Formula: see text] 0.536, n = 17). We conclude that canopy gaps and understory vegetation, rather than forest maturity, appear to be the limiting factors affecting the selection of a site by hooded warblers. Further research should focus on the use of gaps by breeding hooded warblers, and logging prescriptions should be formulated to include the creation of openings in the forest canopy.