The Canada Warbler is a little-studied species that typically breeds in cool, moist forests of the United States and Canada. A long annual migration takes it to its wintering grounds in northern South America, where habitat loss is a threat. Habitat degradation and loss on the breeding grounds has also negatively affected populations.
Identification
The distinctive black markings across an otherwise yellow throat and
breast gives this warbler the nickname of "Necklaced Warbler." The unmarked
back and wings are slate-gray, edging towards black on the crown, and a
white eye-ring boldly characterizes the face. The female is similar to the
male, though the necklace is less distinct and the face and crown are more
olive-gray than black.
The clear, loud song is extremely variable, consisting of a chip note
followed by an abrupt, explosive series of short notes that invariably ends
with a 3-note phrase, the last one loud and rising in pitch. The song is
often described as chip chupety swee-ditchety or chip, suey de
swee-dictchety.
Distribution and Population
Trends
During the breeding season, the Canada Warbler's range stretches from
northeastern British Columbia and northern Alberta across southern Canada to
Nova Scotia. This species can be found in many types of forest in central
Minnesota, the Great Lakes region, New York, and New England. It is also
found at higher elevations in the southern Appalachians, stretching south
from New York, through Pennsylvania and New Jersey to western North Carolina
and northern Georgia. Canada Warblers breed in a number of Audubon Important
Bird Areas including New York's Moose River Plains and Catskill High Peaks
IBAs and North Carolina's Roan Mountain IBA.
It winters in northern South America, including
Venezuela, Colombia, Ecuador, Peru and northern Brazil.
Canada Warblers are not abundant within most of the breeding distribution,
and based on Breeding Bird Survey (BBS) results from 1966 - 2001,
populations have declined at rate of 1.9% per year throughout the breeding
range. The most severe declines are in the northeastern U.S., perhaps a
result of a change in forest structure over the past century. Optimal
habitat may have been provided as previously farmed land regenerated to
forest, but disappeared as the forest matured and eliminated the understory.
Forested wetlands, also suitable for Canada Warbers, have been drained,
filled, and developed during the 20th century.
Ecology
Birds leave the wintering grounds between late March and mid-April and
arrive on the breeding grounds between mid-May and early June. Important
stopover habitats include bushes and vine tangles near the edge of parks,
villages, and cities, and thickets of stream and woodland edges, swamps and
willow trees.
The Canada Warbler will inhabit many types of forest during the breeding
season, primarily coniferous and mixed northern hardwood forests with dense,
often wet, undergrowth. They appear to prefer limited ground cover, but high
foliage density in the shrub layer. Little is known about territoriality,
but the male appears to arrive on the breeding grounds before the female and
aggressively defends a territory by singing. The female builds the nest
alone, it is usually placed on or just above the ground among ferns, stumps,
and fallen logs, or, in the southern part of its range, in rhododendron
thickets. Dense nest site cover appears to be important habitat requirement.
There is little information about the incubation and nestling periods, but
it appears the incubation period is performed only by the female and lasts
for about 12 days. During the nestling period, which lasts for about 10
days, both parents feed the nestlings. Fall migration starts in mid-July to
late August, the first individuals typically arrive on the wintering grounds
by early September.
Their diet consists of flying insects and spiders, captured by flycatching
or gleaning prey from both conifers and deciduous trees, or off of the
ground.
Threats
Sensitive to forest fragmentation and human disturbance, populations have
been apparently negatively affected on both the breeding and wintering
grounds due to habitat loss and degradation. Extensive cutting and forest
fragmentation in eastern deciduous forests has reduced this bird's breeding
habitat. Nest predation is higher in fragmented forests. Populations that
breed in the southern Appalachians are particularly vulnerable to habitat
loss and degradation from air pollution, especially acid rain, since they
only nest in sensitive spruce-fir habitats at high elevations. Loss of
coniferous habitat from infestations of the Woolly Adelgid are a major issue
in much of the species southern breeding range. Habitat loss on the South
American wintering grounds may continue without decreases in human
population growths and changes in policies toward habitat conservation.
Conservation
Although little conservation work has been directly focused on the
Canada Warbler, much land has been purchased for conservation purposes
throughout its range which likely benefits the species. Audubon New York's
Forest Biodiversity Stewardship Program is developing landowner outreach and
educational materials for how private forest landowners can manage for
Canada Warblers and other forest-dependent species through various forestry
techniques. To find out more visit:
http://ny.audubon.org/FOREST/index.html
Canada Warbler is listed as a priority species in Partners in Flight's Bird Conservation Plan for the Adirondack Mountains, an area where the species reaches some of its highest breeding densities (http://www.partnersinflight.org). One of the objectives of this plan is to ensure the availability enough northern hardwood/mixed forest suitable to support 15,000 - 20,000 breeding pairs of Canada Warbler distributed among 600-700 atlas blocks.
