Monday, April 26, 2010

Vaux's Swifts: amazing aerialists

Vaux's SwiftVaux's Swift, Fernhill Wetlands, Forest Grove, Oregon on 22 September 2009 by Greg Gillson.


The Vaux's Swift might be thought of as a Pacific NW breeding specialty, occurring from SE Alaska across southern British Columbia and northern Idaho, south in the wooded mountains into central California. They winter mostly from southern Mexico to Panama.

However, there are also non-migratory Vaux's Swifts in Mexico, Panama, and northern Venezuela. These are sometimes considered a separate species, Dusky-backed Swift, Chaetura richmondi.

Vaux's Swifts arrive in the latter half of April in the Pacific NW and form large migratory flocks in September as they head south. Large migratory flocks of swifts roost at night in brick chimneys. One famous roost is in downtown Portland at the Chapman Elementary School. By mid-September 10-35,000 swifts may use this roost. This has become quite the local spectacle, and problem, with some 400-2000 people visiting each night to watch, according to the Audubon Society of Portland.

These swifts may choose to nest in chimneys in towns, but often use hollow snags in the forest. They build their nests of saliva and small twigs. During the day they forage over woods, waters, and towns with high, buzzy twittering calls.

Though they may look superficially like swallows, there are many differences. Swifts have weak feet and cannot perch on tree branches or wires. They cling to the inside of hollow snags or chimneys at night, but spend most of the day in speedy flight. They are dusky gray with paler throat and rump. The wings have the wrist joint very near the body, thus they have twinkling flight and brief soaring. Their tail feathers are short and bristle-like.

This swift was named in honor of American minerologist William Vaux (1811-1882). Since he pronounced his name as "vawks," that is the pronunciation of the name of the swift, not "voze" as it might be pronounced if French.