Bay-breasted Warbler

Taxonomy/Description

The Bay-breasted Warbler is a passerine in the family parulidae. This family contains all of the species of wood warblers in the new world. It is in the genus Dendroica – consisting of northern warblers. The Bay-breasted Warbler is one of the largest warblers in Dendroica at about 14cm in length and weighing an average of 13g. The immature and basic plumage of the Bay-breasted Warbler consists of an olive green head, nape, and back with very thin black streaks, cream colored belly, and occasionally rusty tinted sides. The male breeding plumage shows the same creamy undersides, two distinct white wingbars, a black face and chestnut on the crown, throat, and sides. The breeding female differs in that markings and color is not as bold and she will lack black face coloration, chestnut cap and throat. The Bay-breasted Warbler in basic plumage is, at times, confused with the Blackpoll and Pine Warbler, however, with noting slightly chestnut sides, pure unstreaked underparts, streaked back, and dark legs and feet a positive identification of the Bay-breasted can be made.

Habitat/Diet

The distribution of the Bay Breasted Warbler in North America is correlated with spruce and balsam fir forests. Its range is mostly the Central and Eastern boreal forests of Canada. In fact, ninety percent of its breeding range is found in Canada – the other ten percent in the U.S. This shouldn’t be discouraging for Western New York birders, however, because the Bay Breasted Warbler can be found in W.N.Y. during the bird’s migration season and this warbler spends less than 30% of the year on its breeding ground. During migration the Bay Breasted Warbler is not restricted to coniferous trees alone. They usually will be spotted in the midlevel to canopy of a forest. Insects and spiders make up the majority of the Bay Breasted Warbler’s diet, especially during the rainy season – from October to December. When insects are scarce, fruits are consumed.

photo M. Noonan

Behavior/Reproduction

The Bay Breasted Warbler is a rather aggressive warbler. Males are very territorial and can be seen chasing one another on breeding grounds. This bird is typically solitary and territorial when food supplies are low. When food is abundant, territories are given up and they forage in flocks. However, aggression peaks during times of high food supplies. Bill snapping is associated with attack and raising of the crown feathers is associated with alarm. Against other warblers, the Bay Breasted is usually the more aggressive competitor. This warbler’s larger body may not always make it the most social dominant interspecifically, but it does allow it to have more opportunistic feeding behavior.

Because there have been no reports of polygamy, Bay breasted warblers have been presumed to be monogamous. A loosely woven and fragile nest is usually built in the lower third of a tree, mainly by the female. There is usually only one clutch per season with five eggs being typical. The female incubates alone while the male perches on a nearby tree and sings. When the nest is approached by female, she will begin to flap wings with her tail spread – supposedly to fake injury.

Where to see them in WNY

At times the Bay Breasted Warbler has been heard and found on Swallow Hollow Nature Trail in Iroquois National Wildlife Refuge.