the olive-sided flycatcher , contopus cooperi , is a passerine bird .
it is a medium-sized tyrant flycatcher .
adults are dark olive on the face , upperparts and flanks .
they have light underparts , a large dark bill and a short tail .
the song is a whistled quick-three beers .
the call is a rapid pip pip pip .
contopus borealis is a junior synonym of contopus cooperi , according to the 1997 aou checklist , quoted by bison .
the name of this species is listed as contopus borealis in many older guides .
their breeding habitat is coniferous woods across canada , alaska and the northeastern and western united states , and other types of wooded area in california .
olive-sided flycatchers are abundant in early postfire landscapes that have burned at high severity .
these birds migrate to central america and the andes region of south america .
they wait on a perch at the top of a tree and fly out to catch insects in flight .
the female usually lays 3 eggs in a shallow open cup nest on a horizontal tree branch .
the male defends a large area around the nesting territory .
both parents feed the young birds .
the numbers of this bird are declining , probably due to loss of habitat in its winter range .
