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Black-and-white Warbler
PARULINE NOIR ET BLANC
Mniotilta varia (Linnaeus)
Fairly common breeder in the
southern half of the boreal forest; common migrant elsewhere in the south.
Many warblers glean insect
life from leaves and twigs, but the Black-and-white Warbler usually forages
like a nuthatch along tree trunks and branches for wood-boring insects and
dormant larvae. The legs and feet are modified for this behaviour—the main
reason that the species is classified in a separate genus from Dendroica.1
This specialization allows this rather tame little bird to reach its breeding
grounds a week or two ahead of most other warblers in the spring.
This boldly striped
species is readily identified in all plumages, though the buffy wash and
limited streaking on some immature birds can be confusing. The male’s primary
song is high-pitched, with a rhythmic, sawing quality, weesee-weesee-weesee…,
that distinguishes it from the Cape May Warbler and other high-frequency
singers. Less often heard is the sweet and complex alternate song.
This species reaches
Manitoba in late April and becomes well established in the first half of May.
Fairly common and widespread in much of the south, it represents about two
percent of the warblers banded at Delta Marsh Bird Observatory in both spring
and fall, but is relatively scarce in the extreme southwest.2
Migration is concentrated mainly in May, August and early September; spring
departure and fall arrival dates south of the boreal forest are difficult to
define, because the breeding range includes much of the aspen-parkland region.
Frequent stragglers occur well into October, while an exceedingly late bird
survived on a diet of peanut butter at a Winnipeg feeder until 20 November 1997.3
The breeding range
spans eastern North America from Texas to Newfoundland, and extends west across
much of Canada. In Manitoba the species is most numerous in deciduous and
mixed-wood portions of the southern boreal forest, from the Whiteshell–Nopiming
region north and west to Grand Rapids, Easterville and Overflowing River.
Farther south, this warbler also occurs in extensive aspen bluffs, boreal
“islands” and wooded river valleys. Northerly localities include The Pas,
Thicket Portage, and Grass River Provincial Park. The range limit is probably
near the upper Churchill River system;4 the species has not been
reported at Thompson, and there is just one report for the intensively studied
Churchill region, a lone bird on 15 June 1966.5
Black-and-white
Warblers have been recorded on 31 different Breeding Bird Survey routes,
including many in south-central and southwestern regions that average only one
or two birds. Bird River is the leading route, with a peak count of 20 birds
and an average of 10, closely followed by several other routes in southeastern
and west-central Manitoba. There are just four cards in the Nest Record file
for this ground-nesting warbler, with egg dates from 7 to 27 June and nestlings
observed on 23 June and 6 July.
1 Parkes 1978; 2 Knapton 1979a; 3 Yvette & Harold Kelly, confirmed by R.F. Koes; 4 Koonz
& Storey 1975; 5 Jehl & Smith 1970.
S. Edie, J.
Maynard, P. Taylor
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