Habitat use and foraging behavior of four parulid warblers in a second-growth forest

-Habitat use and foraging behavior of the Chestnut-sided Warbler (Dendroica pensylvanica), Canada Warbler (Wilsonia canadensis), Mourning Warbler (Oporornis philadelphia) and Nashville Warbler (Vermivora ruficapilla) were studied in a second-growth forest in northern Wisconsin (USA) during the breeding season. Our objective was to determine if interspecific and intersexual foraging differences exist among these species. The warblers concentrated foraging activities on a few species of trees and shrubs. Compared to other species, Canada Warblers more frequently used coniferous trees that were scattered through the primarily deciduous habitat. All species most frequently used branches of trees, but male Nashville Warblers also made considerable use of leaves and twigs. Warblers foraged at a variety of heights in the vegetation, with male Nashville Warblers foraging highest in the midstory and canopy of mature trees. Females of all species tended to be active lower in the vegetation than males. Gleaning was the most frequently used foraging method, except for male Canada Warblers, which used foraging methods involving flight in about 70% of prey pursuits. When 30 foraging-related characters were considered simultaneously in a multivariate analysis, it was found that intersexual differences within a species were less pronounced than interspecific differences, except Nashville Warbler males, which were distinct in their foraging. When designing a conservation strategy for these species, biologists must recognize that these birds require heterogenous second-growth forests. UTILIZACION DEL HABITAT Y CONDUCTA DE FORRAJEO DE CUATRO ESPECIES DE PARULIDOS EN UN BOSQUE SECUNDARIG Sinopsis. -Se estudi6, en un bosque secundario al norte de Wisconsin, el uso de habitat y la conducta de forrajeo de Dendroica pensylvanica, Wilsonia canadensis, Oporornis philadelphia y Vermivora ruficapilla, durante le 6poca reproductiva de dichas aves. El objetivo fue determinar si habia diferencias interespecificas e intersexuales entre las diferentes especies. Las aves concentraron su actividad de forrajeo en un grupo reducido de especies de airboles y arbustos. En comparaci6n a otros estudios Wilsonia utiliz6, con mayor frecuencia, coniferos que estaban esparcidos a traves de un habitat de deciduos. Todas las especies utilizaron con mayor frecuencia las ramas de los arboles, aunque los machos de Vermivora utilizaron considerablemente a las hojas y a las ramitas. La altura de forrajeo fue variable con Vermivora utilizando la parte mas alta del docel y el estrato medio de la vegetaci6n madura. A menor altura en la vegetaci6n, las hembras de todas las especies tendieron a estar mais activas que los machos. El rebusque result6 ser el metodo de forrajeo utilizado con mayor frecuencia, a excepci6n de los machos de Wilsonia que utilizaron metodos asociados al vuelo en el 70% de los casos. Cuando se consideraron en una analisis de multivarianza, simultaneamente, 30 caracteres relacionados al forrajeo, se encontr6 que las diferencias intersexuales dentro de una especie eran menos pronunciadas que las diferencias interespecificas, excepto para los machos de Vermivora que fueron distintos en su forrajeo. Cuando se planifique disefiar una estrategia de conservacion para estas especies, los bi6logos deben reconocer que estas aves requieren de bosques secundarios heterogeneos. 1 Current address: Laboratory of Wildlife Conservation, National Institute for Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305, Japan.