0 the bay-breasted warbler , dendroica castanea , is a new world warbler .
1  they breed in northern north america , specifically in canada , into the great lakes region , and into northern new england .
2 these birds are migratory , wintering in northwest south america and southern central america .
3  they are very rare vagrants to western europe .
4 this species is closely related to blackpoll warbler , but this species has a more southerly breeding range and a more northerly wintering area .
5 the summer male bay-breasted warblers are unmistakable .
6  they have grey backs , black faces , and chestnut crowns , flanks and throats .
7  they also boast of bright yellow neck patches , and their underparts are white .
8  they have two white wing bars , as well .
9  breeding females essentially resemble washed out versions of the male .
10  the females are greyish above and white below , with much weaker head patterns .
11  the females also only have chestnut markings on small flank patches , although tiny tints in their grey crowns have been observed .
12 non-breeding birds have greenish heads , greenish upperparts and yellowish breasts .
13  the yellow extends to the belly of young birds .
14  the two white wing bars are always present in every stage of life .
15  these birds differ from non-breeding blackpoll warblers in the absence of breast streaks .
16 their breeding habitats are coniferous woodlands .
17  bay-breasted warblers nest in conifer , laying 3-5 eggs in a cup-shaped nest .
18  more eggs are laid in spruce budworm years .
19  these birds feed on insects , and the numbers of these birds vary with the abundance of the spruce budworm .
20  these birds will also feed on berries and nectar in wintertime .
21 their songs are repetitive high-pitched si si si's .
