- 5.5 in
- 7.9–8.7 in
- 0.4–0.6 oz
- Paruline à poitrine baie, Fauvette à poitrine baie (French)
- Reinita pecho bayo, Reinita castaña (Spanish)
- The Bay-breasted Warbler is closely related to the Blackpoll Warbler, and hybrids between the two species are known. The Bay-breasted Warbler is known to hybridize also with Yellow-rumped and Blackburnian warblers.
- Adult Bay-breasted Warblers appear to follow a more western migratory route south in the fall than first-year birds. More adults migrate west of the Appalachian Mountains than east of them, while first-year birds are frequent along the coast.
- In contrast to the more stable populations of other warblers, Bay-breasted Warbler numbers go up and down depending on outbreaks of the spruce budworm. It is abundant during infestations, but declines or even disappears from some areas a few years later.
- The oldest known Bay-breasted Warbler was at least 4 years, 11 months old.
Breeds in boreal spruce and fir forest. Winters in lowland tropical forest and second growth.
Insects and spiders, fruit in winter.
- Clutch Size
- 4–7 eggs
- Egg Description
- White or creamy with bold dark spots.
- Condition at Hatching
- Helpless with sparse brown down.
Nest an open cup of twigs, bark, lichen, spider web, and plant down; lined with fine rootlets, pine needles, hair, moss, and fine grasses. Placed on limb of dense spruce tree.
Gleans insects off leaves and branches in middle part of trees.
Populations of Bay-breasted warbler appear to be decreasing throughout their range. The U.S. has seen a decline of almost 3% per year between 1966 and 2014, resulting in a cumulative decline of 74%, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 9 million birds with 99% breeding and migrating through Canada, and 1% in the U.S. They rate a 12 out of 20 on the Continental Concern score and are a U.S.-Canada Stewardship species. They are not on the 2014 State of the Birds Watch List. Population declines are possibly as result of spraying for spruce budworms, and loss of wintering habitat may be a problem.
- Williams, J. M. 1996. Bay-breasted Warbler (Dendroica castanea). In The Birds of North America, No. 206 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.
- Dunn, J. L., and Garrett, K. L. 1997. A Field Guide to Warblers of North America. Houghton Mifflin Co., Boston.
- North American Bird Conservation Initiative, U.S. Committee. 2014. State of the Birds 2014 Report. U.S. Department of Interior, Washington, DC.
- Partners in Flight. 2012. Species assessment database.
USGS Patuxent Wildlife Research Center. 2015. Longevity records of North American Birds.
- USGS Patuxent Wildlife Research Center. 2014. North American Breeding Bird Survey 1966–2014 Analysis.