American Birding Podcast



A Black Swift secret revealed

Swifts have never been ones to reveal their secrets freely, just where these sickle-winged aerialists went in the winter being perhaps the most well-guarded.  In fact, not that long ago even preeminent naturalists like Elliott Coues were inclined to fall back on odd theories for their abrupt departure, giving some credence to the ludicrous idea that the birds buried themselves in the mud and hibernated until spring.  

It wasn't until 1944 that the wintering grounds of even the wide-ranging Chimney Swift (.pdf) were discovered when a band of Peruvian indigenous people more or less unceremoniously presented local missionaries with a chain of aluminum bands previously affixed to birds banded from Ontario to the Gulf coast.  That discovery of that species' wintering grounds was one of the most significant ornithological findings of the last century, but not for another 70 years could we say the same for all the North American swifts.

The Black Swift, Cypseloides niger, is not only the largest swift in North America, but undoubtedly the most mysterious.  It was one of the last birds on the continent to be scientifically described.  Its nest, tucked behind mountain waterfalls in the high altitudes of the west, wasn't discovered until 1901.  And perhaps most amazingly, it is the only species of bird in North America whose wintering range was unknown going into the 21st Century.  

Until now.  

In 2009, a group of researchers primarily from the Rocky Mountain Bird Observatory but including other government and non-profit organizations, netted several Black Swifts at a known colony in Colorado and affixed to them a tiny geolocator in the hopes that, at some point in the future, those birds would return to be netted again, and the mystery would finally be revealed.  It took a few years, but three of the four tagged swifts were recaptured and the remarkable results published just last week in the Wilson Journal of Ornithology

BLSWmigrationThe Black Swifts traveled all the way from Colorado, from those nest sites in the high Rockies, to the Amazon, where they spend the cold months in western Brazil.  For more, I turn to Nathan Pieplow of the great

The colored blotches in the western Amazon are the areas where the swifts likely spent most of the winter.  They’re blotchy because the geolocators aren’t terrifically accurate, and also because the swifts apparently  moved around a fair amount during the winter.  It’s possible that they roosted in caves or cliffs for the night and then roamed extensively during the day, but the researchers raise the tantalizing possibility that wintering Black Swifts may actually stay aloft 24 hours a day, based on the behavior of the related Common Swift of Eurasia, which may be on the wing for up to 9 months of the year — or even several consecutive years, in the case of non-breeding individuals!

The authors stress, however, that no conclusions about roosting behavior can be drawn from the current study.  If the wintering birds do roost in dark crevices like they do in summer, they could skew the geolocator data, which is based on light levels.  Extensive cloud cover could also be an issue.  There’s evidence of at least some errors in the migration tracks at right: the researchers stress that bird 554 did not, in fact, probably take a quick jaunt to the Pacific Ocean off of Baja California after arriving in Colorado — that data point is likely due to some type of irregular shading event that messed up the geolocator data.  Nevertheless, the generally strong agreement between the tracks of the three birds provide a reasonable level of confidence about the quality of the data.

There's no shortage of fascinating tidbits and ramifications to pick through with this paper, not least of which is the revelation that all three birds appear to travel north by way of Texas, a state that has zero records of Black Swift on the state list.  What to do there? 

For more information on this truly amazing bird, and to put this recent finding in greater context, please have a look at the eBook, The Coolest Bird (.pdf), written by Rich Levad and published by the ABA.