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Incidence of nest material kleptoparasitism involving Cerulean Warblers.

Article Excerpt
The Cerulean Warbler (Dendroica cerulea) is a canopy-nesting bird of eastern deciduous forests. Nests of this species are composed mainly of bark fiber, fine grass stems, weed stalks, hairs, spider webs, grapevine bark, lichen, and moss (e.g., Bent 1953, Ehrlich et al. 1988, Oliarnyk and Robertson 1996, Hamel 2000). Nests are typically on horizontal branches and are concealed from above by nest-tree and/or vine foliage (Bent 1953, Hamel 2000, Roth 2004). Few published studies have documented interspecific nest kleptoparasitism involving Cerulean Warblers. Hamel (2000) noted in the Mississippi Alluvial Valley that Cerulean Warblers and American Redstarts (Setophaga ruticilla), and Cerulean Warblers and Blue-gray Gnatcatchers (Polioptila caerulea) interacted aggressively over nesting materials. Cerulean Warblers have also been observed gathering nesting materials from vireo nests (species unspecified) in New Jersey (Dater 1951).

Cerulean Warbler breeding biology studies have focused on nest observation beginning in 1992 in Tennessee and Arkansas, and in 2002 in southern Indiana. This paper documents 21 interspecific contests for nesting material involving Cerulean Warblers that were observed during stages of the nesting cycle (Table 1). We present three detailed accounts of nest material kleptoparasitism involving Cerulean Warblers as both victim and perpetrator. Owner defense usually started at the point at which the owner discovered the robber at its nest.

OBSERVATIONS

The following two accounts document nest material kleptoparasitism with the Cerulean Warbler as victim. The first incident occurred on 19 May 2003 between 1230 and 1300 hrs CST when a Red-eyed Vireo (Vireo olivaceus) was observed taking material from a Cerulean Warbler nest in a grove of black walnut (Juglans nigra) at Big Oaks National Wildlife Refuge (39[degrees] 03' N, 85[degrees] 25' W) near Madison, Indiana. The vireo landed on the nest branch within a meter of the nest, then flew to the nest and removed a piece of the outer cup when the Cerulean Warbler was not present. The nest material was sufficiently large to be seen in the vireo's beak as it flew to a more densely wooded area. No bird visited the nest for a period of several minutes until a vireo again landed on the nest branch. The vireo hopped toward the nest when the male Cerulean Warbler chased it into the heavily wooded area. The female Cerulean Warbler then flew to the nest and sat in it. The female Cerulean Warbler was first observed building the nest on 8 May and incubating on 17 May. She was last observed incubating on 29 May and the nest had failed on 31 May. The walnut grove had...