Threats and Population Declines
Unfortunately, the golden-winged warbler is a bird species in peril. Breeding Bird Survey results indicate a range wide population decline of 2.3% annually since 1966 with the Pennsylvania golden-winged warbler population declining by 6.8% per year over the same period. The species is also breeding in fewer places across the commonwealth than it did 20 years ago. The 2nd Pennsylvania Breeding Bird Atlas (2004-2008) demonstrated a distribution decline of 63% since the first PBBA (1984-1989).
The cause of golden-winged warbler population declines is primarily due to loss of suitable breeding habitat. Golden-winged warblers depend on regular ecological disturbance, like wildfires or insect outbreaks, to maintain prime early successional habitats by interrupting the natural process of open habitats reverting to forests. Natural forest succession from young to mature forests, and changes in management practices like wildfire suppression have reduced the amount of suitable habitat available across the landscape. Shifts in farming practices and development have also contributed to the loss of golden-winged warbler habitat.
To further complicate the situation, golden-winged warblers face another opponent in the form of its close relative the blue-winged warbler (Vermivora cyanoptera). Both species occupy early successional breeding habitats and compete for resources, and where their ranges overlap, the two species can interbreed or hybridize. The resulting hybrid offspring share mixed characteristics of both species including plumage and song. Although a variety of traits can appear in hybrids, two forms are commonly observed: Brewster’s warbler – a cross between two pure parents, and Lawrence’s warbler – a cross between a pure parent and a fertile hybrid. In Pennsylvania, the concern with hybridization is that blue-winged warblers and resulting hybrids appear to be squeezing out golden-winged warblers from more marginal habitats, thus reducing populations and limiting distribution to mostly higher elevations of the central Appalachians.
Other factors contributing to declining golden-winged warbler populations include nest parasitism by the brown-headed cowbird (Molothrus ater) and continuing loss of wintering habitat in Central America, Colombia, and Venezuela.