Adult females, autumn adults of
both sexes and juveniles closely resemble sparrows with striped
upper parts and sparrow-like bills. Adult male in breeding plumage
has head and under parts black, large buff patch on back of neck,
upper back streaked with buff. Rest of back, rump, upper tail coverts
and scapulars pale grey to whitish. Wing and tail black with yellowish
edging. Overall length
16 -20 cm (Godfrey, 1986).
Distribution
Columbia Basin: Creston Valley and
southwest corner of the Columbia Basin.
British Columbia: Breeding is locally
distributed in the main valley bottoms in the southern and central
interior, east to Creston.
Global: Breeds from s. British Columbia
east to the Maritime Provinces and sw. Newfoundland, south to Oregon,
Nevada, Utah, Colorado, Kansas, Missouri, Illinois, Ohio, Pennsylvania
and locally south to North Carolina. Winters in South America, east
of the Andes, from Peru, Bolivia and c. Brazil south to n. Argentina
(Cannings et al. In prep.).
Habitat
Fields, marshes and meadows of tall
grass, clover, alfalfa, or grain. This neotropical migrant nests
in fields of tall grass, particularly large established hayfields
and moist meadows. In British Columbia it nests, often semi-colonially,
in cultivated fields between 300 and 800 m elevation (Cannings et
al. In prep.).
Threats
Recent population trends are considered
to be downward due to ongoing urbanization of lowland valleys and
more intensive farming practices, but empirical data is lacking.
Bobolinks colonized British Columbia shortly after the turn of the
century, likely by taking advantage of newly created agricultural
habitats. Moderately threatened by habitat loss due to urbanization,
particularly in the Okanagan Valley. Increasingly intensive haying
practices and conversion from grass to alfalfa hay crops also negatively
impacts breeding populations. Hay cropping during incubation and
early nestling stage results in 100% loss of offspring. Application
of insecticides to breeding areas both reduces and contaminates
their primary food source, impacting both juvenile and adult birds
(Cannings et al. In prep.).
Biology
The nest is flimsily constructed
of grasses and weed stalks, and is well concealed, usually on the
ground in a small hollow at the base of tall weedy plants. Bobolinks
are polygamous and feed on insects and seeds when they first arrive
on the breeding grounds in mid-to-late May, switching more to insect
and spider prey later in the season as the young hatch. They feed
on seeds (often rice) during migration and over-wintering. Fall
migration begins from late July to mid-August and very few birds
remain by the end of August. They winter south of the equator in
South America. In British Columbia the average clutch size is four,
and varies from 2 to 6 eggs Incubation, solely by the female, is
reported to last 10 - 13 days. The nestling period is 10 - 11 days
(Cannings et al. In prep.).
