Bay-breasted Warbler

 

Common Name:Bay-breasted Warbler

Class:Aves

Order:Passeriformes

Family:Parulidae

Genus:Setophaga

Species:Setophaga castanea

Photo: M. Noonan

 

TAXONOMY

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. The Bay-breasted Warbler is one of the largest warblers in Setophaga at about 14cm in length and weighing an average of 13g. 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 the black face coloration, chestnut cap and throat. An immature and basic plumage of the Bay-breasted Warbler has an olive-green head, nape, and back with very thin black streaks, cream colored belly, and occasionally rusty tinted sides. The Bay-breasted Warbler in its autumn basic plumage may be confused with the Blackpoll and Pine Warber. The Bay-breasted Warbler can be distinguished by noticing slightly chestnut sides, unstreaked underparts, and darker legs.

Photo: M. Noonan

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 WNY 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 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

 

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 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 socially dominant species of bird, but it does allow it to have more opportunistic feeding behavior.

There have been no reports of polygamy in Bay-breasted Warblers so the species 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 5 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. The female incubates the eggs for 12-13 days. The chicks are born altricial which means they are blind, immobile and helpless. Both males and females will tend the young until they fledge which is 11-12 days after they hatch.

 

WHERE TO FIND THEM

 

During the peak of migratory season Bay-breasted Warblers may be found in coniferous trees Forest Lawn and at times has been seen in other areas of Buffalo in wooded areas before continuing to their breeding grounds.

 

Birds of Western New York is brought to you by the Institute for the Study of Human-Animal Relations at Canisius College in Buffalo, NY.