Behavioral Interactions between Golden-Winged and Blue-Winged Warblers

Abstract

The breeding range of the Golden-winged Warbler (Vermivora chrysoptera) has expanded in some regions and contracted in others for more than a century (Gill 1980). The decline of the Golden-winged Warbler often is attributed to loss of breeding habitat and/or interactions with the Blue-winged Warbler (V pinus; Confer and Knapp 1977, 1981; Will 1986; Hands at al. 1989; Confer 1992a,b). Golden-winged Warblers nest in early successional habitat. Abandoned farmland is the precursor of most its nesting habitat, although fires, lumbering, and powerline maintenance also create habitat (Hands et al. 1989). The decline of the Goldenwinged Warbler is part of a widespread reduction in early successional species (Sauer et al. 1997) that is correlated with habitat loss. For example, abandonment of farmland in New Hampshire peaked about a century ago, and early successional habitat was most abundant from 1900 to 1955 (Litvaitis 1993). Since 1955, early successional habitat has decreased to nearly zero. Similar loss of habitat has occurred throughout the reforested northeastern United States, and the abundance of Golden-winged Warblers and other early successional birds has declined (Hill and Hagan 1991, Witham and Hunter 1992, Smith et al. 1993). At the other extreme, the rate of farmland abandonment has increased in Pennsylvania, Minnesota, and Wisconsin from 72,000 ha per year during 1925 to 1960 to 185,000 ha per year from 1960 to 1990 (Census of Agriculture 1935, 1992). Numbers of Golden-winged Warblers increased from 1980 to 1996 (Sauer et al. 1997). Within forested habitats, bird species turnover may continue as young forests mature (Holmes et al. 1986). Rappole and McDonald (1994) speculated that Golden-winged Warblers (but not Blue-winged warblers) have been seriously reduced in numbers as a result of winter-habitat loss.... However, regional declines of Golden-winged Warblers began more than 90 years ago (Gill 1980), before loss of winter habitat was extensive, and their numbers are increasing in the northern portions of their range (Sauer et