Swamp forests and uplands in southern New York:
A source-sink landscape that allows the exceptional coexistence of Golden-winged and Blue-winged Warblers.
The Golden-winged Warbler was once fairly common throughout much of New England yet the Golden-winged Warbler Atlas Project sponsored by the Laboratory of Ornithology recently found only 15 pairs in this entire region. The New Jersey Fish and Game found that the number of territorial males has declined from 200 in 2002 to less than 24 in 2008. Breeding Bird Atlas Surveys in New York and New Jersey show a 55% to 60% decline for both states in the last 20 years.
Although the loss of disturbance ecosystems is a major cause of this decline, the near or total elimination of Golden-winged Warblers from much of its range is associated with the intrusion of Blue-winged Warblers, perhaps because of some combination of competition and hybridization. In many areas, the virtual elimination of Golden-winged Warblers has occurred despite the presence of suitable habitat. Management of utility rights-of-ways in Massachusetts alone provides over 30,000 acres of habitat that is more suitable for Golden-winged than Blue-winged Warblers, yet my surveys of 380 locations on utility rights-of-ways across New England found only Blue-winged Warblers.
Southern New York is unusual in that it has supported both species for a prolonged time. Golden-winged Warblers in local uplands experiences high predation, frequent hybridization, and have a high level of genetic mixing with Blue-winged Warblers. In swamp forests, the nesting success is high as predation by eastern chipmunks and black rat snakes is near zero, there is low hybridization because there are very few Blue-winged Warblers, and the Golden-winged Warblers have a high degree of genetic purity. Thus, Golden-winged Warblers in swamp forests produce a large number of genetically pure young, enough to sustain the population in swamps and uplands.
Attempts to manage uplands as early successional habitat appear to have failed since Blue-winged as well as Golden-winged Warblers were attracted to the disturbance sites. Currently, the suitability of swamp forests for Golden-winged Warblers is threatened by the invasive growth of Phragmites, which are avoided by Golden-winged Warblers. We are trying to get support to study the effect of water level management on Phragmites and subsequent nesting density and nesting success for Golden-winged Warblers in a wide range of swamp forests.