Scientific Name:
Dendroica caerulescens
Nest Type: Cup
Nest Location: Shrub,
coniferous tree; 0.5-3'
Clutch Size: 3-5,
avg. 4
Food: Insects
Foraging Guild:
Hover glean, foliage gleaner, hawks
The Black-throated Blue
Warbler is a rare and local summer resident in Minnesota. Breeding birds
can be found consistently mainly in the mature sugar maple forests of
Lake and Cook counties (Eckert 1983). The overall breeding distribution
of the species extends from Nova Scotia and New Brunswick, south along
the Atlantic Coast and into the Applachian mountains to western North
Carolina, and west around the Great Lakes to northeastern Minnesota
(National Geographic Society 1983). In Minnesota, spring migration usually
occurs in early to late May. Fall migration may begin in mid-August,
and last through late October (Janssen 1987). This species is one of
the least numerous regular nesting warblers in Minnesota (Janssen 1987)
and Wisconsin (Robbins 1991).
Preferred breeding habitats
in Minnesota, Wisconsin, and Michigan include deciduous habitats usually
dominated by sugar maple, but often mixed with other deciduous trees
such as oak, paper or yellow birch, and aspen (Green and Niemi 1978,
Brewer et al. 1991, Robbins 1991). Coniferous trees such as spruce and
pine are often present, but seldom dominating. Critical characteristics
appear to large deciduous trees, especially sugar maple and a well-developed
understory of deciduous shrubs (Nice 1930, Walkinshaw and Dyer, Freer
1958, Brewer et al. 1991).
Black-throated Blue Warblers
have been identified as sensitive to forest area size. For example,
Finch (1991) classified this species as area sensitive and suggested
minimum area of suitable habitat for breeding at 1000 ha (Finch 1991).
These data, however, were compiled from studies in the eastern United
States where fragmentation into isolated forest areas in an urbanized
and agricultural dominated landscape. The sensitivity of the species
to stand size in a forest-dominated landscape is unknown.
Nests are cup-like in shape
and generally placed in shrubs or small trees (Ehrlich et al. 1988).
In New Hampshire, Holmes (1990) located 66 nests all of which were in
shrubs from 0.1 to 0.9 meters from the ground.
These birds are foliage
gleaning insectivores which specialize in near-surface chase tactics,
and take small to medium sized invertebrates (Black 1975, Robinson and
Holmes 1982). Both sexes forage primarily in the shrub layer, with males
foraging higher than females (Ehrlich et al. 1988). Winter diets consist
of a large proportion of seeds and other plant matter (Ehrlich et al.
1988).
Based on these data, the
species was classified as associated with mature, hardwood forests,
and an area sensitive species.