Golden-winged Warbler (Vermivora chrysoptera) habitat selection, mating behaviour, and population viability in a fragmented landscape at the northern range limit
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The Golden-winged Warbler (Vermivora chrysoptera) is an early-successional specialist and one of the fastest declining songbird species in North America. This decline is related in part to habitat loss and degradation of contemporary forests; however, the consequences of anthropogenic disturbance on the species need further evaluation. Thus, I assessed occupancy, population growth, mating behaviors, and hybrid habitat use by Golden-winged Warblers across a range of disturbance levels within southeast Manitoba, Canada. Golden-winged Warblers consistently responded most strongly to disturbance at the 1-km scale. Forest patches with greater agricultural matrix cover at a 1-km scale were less likely to be occupied by Golden-winged Warblers. However, warblers did select for early-successional habitat created via resource extraction and other anthropogenic disturbances at this scale. Despite higher densities, productivity declined in landscapes with greater edge density because of Brown-headed Cowbird (Molothrus ater) brood parasitism. Additionally, pairing success was reduced in patches with lower forest cover at a 1-km scale, although extra-pair paternity rates were not impacted by patch or landscape characteristics. These results suggest that proximate habitat cues used to select nesting sites may be decoupled from realized fitness in this system. Of the sub-populations I monitored, all showed negative population growth suggesting that anthropogenically disturbed forests may act as ecological traps for Golden-winged Warblers. The most productive habitat for Golden-winged Warbler will have high forest cover and minimal anthropogenic edges. Hybridization with Blue-winged Warblers (Vermivora cyanoptera) has also been suggested as a reason for population declines range-wide and I found that hybridization is now occurring in low levels in the Manitoba population. I found no difference in the habitat used by Golden-winged Warblers compared with hybrids at either a territory or landscape scale. The low proportion of hybrids found in Manitoba and the lack of a distinguishable difference in habitat use by Golden-winged Warblers and hybrids indicates that management efforts to encourage habitat use by Golden-winged Warblers while discouraging habitat use by Blue-winged Warbler are unlikely to be a successful conservation strategy. Instead, management efforts should focus on maintaining or creating early-successional habitats with minimal anthropogenic edges.