WatchList Species Account for Bay-breasted Warbler
(Dendroica castanea)

Qualifies for the list as a Declining Yellow List Species

Photo: Ralph Wright

The Bay-breasted Warbler breeds in the boreal coniferous forests in central and eastern Canada and winters in Central America and northern South America. Its populations rise and fall dramatically with outbreaks of the spruce budworm, which form part of the natural cycle in maturing balsam firs. During one outbreak of spruce budworm in New England, population increases up to 300% occurred due to greater clutch sizes and immigration of conspecifics into the area. Typically, population crashes follow outbreak years.

Recent overall population declines in the warbler may be in part due to insecticide spraying to control the budworm; in addition, high levels of the insecticide have been found in the birds. Changes in forestry practices in eastern Canada such as shorter cutting cycles, large-scale clearcutting and replanting with tree species more resistant to spruce budworm mean less favorable habitat for the bird. In winter its preferred habitat is forest edge and second-growth. The species may be at risk because of habitat destruction on its wintering grounds, where much land has been cleared for cattle grazing.


Adoption of silvipasture practices on the wintering grounds and a more judicious use of pesticides on the breeding grounds—meaning lower dosages and less frequent application—would benefit the species and help reverse its decline.