Scientific Name:
Vireo gilvus
Nest Type: Cup
Nest Location: Deciduous
trees, shrubs; 4-90', avg. 30-90'
Clutch Size: 3-5;
avg. 4
Food: Insects, berries
Foraging Guild:
Foliage gleaner, hover and glean
The Warbling Vireo is a
summer resident throughout Minnesota, except in the northeast and north
central regions where it is usually not found in contiguous stands of
coniferous vegetation, including spruce bogs (Janssen 1987). The species
arrives in Minnesota in late April to early May (Janssen 1987) after
spending the winter in Mexico and Guatemala (Peterson 1980). Fall migration
begins in late July and continues through early September (Janssen 1987).
The species occurs throughout the United States (except the extreme
southeast) and Canada (except the northwest) (Peterson 1980).
The Warbling Vireo prefers
open deciduous woods and fragmented, forested areas (Harrison 1975).
Warbling Vireos prefer to nest in open habitats ranging from open parkland
with isolated trees to small groves in southern Ontario. In Michigan,
the most frequently recorded habitat category was residential-roadside-hedgerow.
They were also recorded in a variety of forest habitats including mesic,
dry, and wet deciduous. Few observations were recorded in mixed forests
and no reports indicated an association with coniferous forests in Michigan
(Brewer et al. 1991). Therefore, this species was classified as hardwood
dependent.
Only one individual was
observed in an extensive survey of northern Minnesota in 1991. This
individual was found in a mature aspen stand in the Chippewa National
Forest (Hanowski and Niemi 1991a). The low number of individuals observed
could be attributed to the types of forest areas sampled. For example,
this survey focused on censusing in larger areas of contiguous forests.
The species generally prefers broken, more fragmented landscapes. Green
(1991) classified it as a species of disturbed/fragmented landscapes.
The Warbling Vireo's nest
is placed in a tree 6 to 20 m from the ground well out from the trunk
(Roberts 1932, Harrison 1975). The average clutch size is 4 eggs and
incubation requires 12 days (Harrison 1975). Caterpillars, moths, and
butterflies comprise the largest portion of the animal diet of this
species (Roberts 1932, Martin et al. 1951). The Warbling Vireo generally
forages in the uppermost portion of trees.
The species has not shown
any significant change in status in the Minnesota during the period
1966 to 1989 based on USFWS Breeding Bird Survey routes (Janssen 1990).
Because the Warbling Vireo prefers open-wooded habitats, it is likely
that this species was much less common during presettlement times (Brewer
et al. 1991). This is likely true in Minnesota, also. Roberts (1932)
describes the bird as relatively rare in most of the forested zones
of Minnesota, but relatively common in the prairie region. As forest
areas are fragmented due to agriculture, urbanization, and forest harvesting
this species has expanded its range into these areas of Minnesota. However,
with reductions in trees in prairie areas and in riparian habitats,
the species has likely become less common (Roberts 1932). It may have
originally been confined to riparian forests and open wetlands with
trees. Because of its association with riparian areas, it was classified
as a riparian species.
The Warbling Vireo would
likely not be affected by increases in forest harvesting in Minnesota
because it prefers smaller forested areas. An additional negative effect
on this species is that it is highly susceptible to Brown-headed Cowbird
parasitism (Bent 1950). The habitats used by the Warbling Vireo coincide
with agricultural lands in which the Brown-headed Cowbird is also quite
common.