Already a subscriber? Sign in Don't have a subscription? Subscribe Now
Bay-breasted Warbler
Setophaga castanea
– Family
Authors: Williams, Janet Mci.
Revisors: Venier, Lisa, and Steve Holmes

Welcome to the Birds of North America Online!

Welcome to BNA Online, the leading source of life history information for North American breeding birds. This free, courtesy preview is just the first of 14 articles that provide detailed life history information including Distribution, Migration, Habitat, Food Habits, Sounds, Behavior and Breeding. Written by acknowledged experts on each species, there is also a comprehensive bibliography of published research on the species.

A subscription is needed to access the remaining articles for this and any other species. Subscription rates start as low as $5 USD for 30 days of complete access to the resource. To subscribe, please visit the Cornell Lab of Ornithology E-Store.

If you are already a current subscriber, you will need to sign in with your login information to access BNA normally.

Subscriptions are available for as little as $5 for 30 days of full access! If you would like to subscribe to BNA Online, just visit the Cornell Lab of Ornithology E-Store.


Adult male Bay-breasted Warbler, OH, 17 May.
Fig. 1. Distribution of the Bay-breasted Warbler.

Editor’s Note: Phylogenetic analyses of sequences of mitochondrial and nuclear DNA indicate that all species formerly placed in Dendroica, one species formerly placed in Wilsonia (citrina), and two species formerly placed in Parula (americana and pitiayumi) form a clade with the single species traditionally placed in Setophaga (ruticilla). The generic name Setophaga has priority for this clade. See the 52nd Supplement to the AOU Checklist of North American Birds for details. Future revisions of this account will reflect these changes.

The Bay-breasted Warbler, a neotropical migrant, inhabits boreal coniferous forests in a broad band across central and eastern Canada. This species breeds primarily in northern spruce (Picea)-fir (Abies) forests, feeding and nesting in the dense foliage of conifers, and typically undergoes significant changes in population density correlated with outbreaks of spruce budworm (Choristoneura fumiferana) and other caterpillars.

Since Bent’s (1953) summary of the life history of this species, several studies have focused on changes in its populations within its breeding range in relation to budworm outbreaks (Venier and Holmes 2010). The decline in spruce budworm populations since the early 1980’s has correlated with reductions of Bay-breasted Warbler populations. During outbreak years, it was estimated that this species typically ate more than 13,000 budworms per hectare in a 41-day period (Crawford and Jennings 1989). Despite these studies within the breeding range of this species, many aspects of its breeding biology remain unknown (e.g., song patterns and repertoire, pair formation, nest selection, and egg-laying.)

The Bay-breasted Warbler winters in Panama and northern South America. An insectivore on its breeding grounds, it eats mostly fruit in Panama during the tropical dry season.

In breeding plumage, males differ markedly from females. Nonbreeding males, females, and juveniles closely resemble Blackpoll Warblers (Setophaga striata) and Pine Warblers (S. pinus) in Basic plumage, making it difficult to distinguish these species. Only since the 1950s have the migration routes of the Bay-breasted Warbler become clarified as people have learned to properly distinguish these three species of confusing fall warblers.

Recently, the Bay-breasted Warbler has been placed on the Partners in Flight Watch List (Rich et al 2004) in the category of moderately abundant or widespread but with declines or high threats. In Canada, which contains over 90% of its range, the Bay-breasted Warbler declined 3% annually from 1970 – 2009 and 5.2 % annually from 1989 to 2009 (Environment Canada 2010). These declines are significantly correlated with decreasing spruce budworm populations, as measured by area defoliated (Venier et al. in review). Although Bay-breasted Warbler has been established as an old forest specialist, it appears to expand its habitat into young and intermediate aged stands in response to budworm outbreaks.