photo Michael Noonan
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 Warbler can be made.
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 Michael Noonan
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 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 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.