In Portland, swifts swoop

A Portland tradition as mind-boggling as it is delightful is back this month along with thousands -- or maybe tens of thousands -- of Vaux's swifts. Portlanders will pack blankets, picnic dinners and binoculars and head to the Chapman School grounds every evening before sunset to watch the avian aerialists swirl in a tornado-like cloud before dropping into the school's tall brick chimney, where they snooze until dawn.

The spectacle occurs each September during the swifts' migration from the Northwest to wintering grounds in Central America and Venezuela. The Chapman chimney is the world's largest known Vaux's swift roost.

Most nights, Audubon Society of Portland stations volunteers at Chapman to answer questions, educate the public about the 4-inch-long birds, and to try, through counting, extrapolating and estimating, to get a handle on how many arrive each night.

In 2009 Audubon volunteers -- swifties, as they're known -- counted 4,000 swifts on Sept. 1; 8,000 on Sept. 15; and 1,700 on Sept. 30. Before 2004, numbers reached as high as 35,000 on a single evening but more recently, high estimates have been about 15,000.