Saturday, October 08, 2005

Chimney Swifts

This evening after the rains had temporarily ended, I walked for a little bit around my neighborhood. I saw a flock of chimney swifts fluttering over the intersection of Massachusetts Ave. and 3rd St., NE; it is a spot where I frequently see them in late summer and during fall migration. Swifts are difficult to count because of their fast flight and flocking habits, but I estimated there were about thirty in this flock. That is a good deal smaller than the peak flocks that I was seeing back in the same general area in September.

Chimney swifts may be one of the few native bird species that benefitted from the urbanization of North America in the wake of the European conquest and Industrial Revolution. They adapted well to nesting in human structures, particularly chimneys and other hollow cavities. (Changes in chimney design may be a cause for concern. See also here.) During the breeding season, swifts will only nest one or two family groups to a chimney, but once the young have fledged, the swifts begin to gather in large flocks that may number in the thousands for a single roosting site.

Now that it is mid-October, we are approaching the late dates for swifts in this part of North America. They will appear in increasingly smaller flocks, until one day there are none, and then we will have to wait to see them again until next spring. My latest date for a chimney swift sighting is October 16; that was set last year in the National Arboretum. The Maryland "Yellow Book" gives November 23 as the late date, but that is clearly an abnormal sighting; most records stop at least two weeks before that date.

When can we expect them to return? The Yellow Book's early date is March 14, but again that is an outlier. Early birds appear around the end of March, and then the full flight comes in late April. My early date is April 18. Between now and then the chimney swifts winter in Peru and the Amazon Basin.

So if you want another look at these characteristic urban birds before next spring, make sure to look up and listen for their chattering during the next two weeks. After that, the swifts will be gone.