Golden-winged warblers can breed with the closely-related blue-winged warbler, producing two hybrid types known as Brewster's warbler and Lawrence's warbler. Hybridization is thought to be contributing to the decline of golden-wings. In Virginia both hybrids have been documented from various locations, although reported numbers have generally been low in both recent times and in the past. A 2006 golden-wing survey of 40 Virginia counties documented 9 hybrid warblers across 7 counties (Wilson et al. 2007), with hybrids comprising 14% of total detections. Other recent studies based in Highland and Bath counties have produced similar results, with 2 hybrids documented in 2005 (A. Weldon, unpublished data), 3 in 2009 (M. Elfner, unpublished data) and 7 (including 3 pairs) in 2010 (Bulluck and Harding 2010). In these instances, hybrids made up between 6 and 21% of total detections. It is not known how the present frequency of hybridization compares to historical levels. The low number of hybrids detected in recent surveys suggests that hybridization is not currently taking place at a high rate.
Complicating the picture is the fact that birds appearing to be normal golden-winged and blue-winged warblers can in fact share genetic material with the other species (genetic introgression). These 'cryptic hybrids' can only be documented through genetic analyses. Analyses conducted for Virginia in 2013 documented cryptic hybrids as comprising 8.3% of a sample of 24 phenotypic golden-winged individuals (L. Bulluck and L. Stenzler unpublished data). Such levels of genetic introgression can be qualified as moderate in comparison to levels in several neighboring states, including Pennsylvania, West Virginia, North Carolina and Tennessee, which range from 4 to 14% (Vallender et al. 2009). Genetic introgression is nearly ubiquitous across the golden-winged warbler's breeding range.
Golden-winged Warbler banner image by Bill Hubick