Spring Black Swift Flocks

Another feature of North Okanagan birding is the regular occurrence of flocks of Black Swifts over Swan Lake, north of Vernon, from about the middle of May through early June. Elsewhere in the Okanagan Valley, things are pretty hit and miss when it comes to seeing Black Swifts at anytime, but late spring is a good time to look for this species over the middle and northern sections of Swan Lake.

The Black Swift is quite simply an amazing bird. Dip into its Birds of North America account by P.E. Lowther and C.T. Collins and you'll find it is a species about which very little is known.

Adult Black Swift on nest at Banff, June 2010. Photo by Chris Charlesworth.

Historical changes in Distribution: No information. Migratory behavior: Little information. Physiology: No information. Winter Range: until very recently unknown. Food selection: No info. Daily patterns of vocalizations: No information. You get the picture.

And yet the Black Swift is, for many birders, a fascinating bird, a species of way more interest than just a checkmark on a life list.

For one thing there's the mysteries of its distribution. Look at the bird's range map and you'll see that Cypseloides niger's supposed ranges across the south two thirds of British Columbia (and yet fewer, probably far fewer, than a half a dozen nests have ever been found in B.C.) south through Washington and Oregon (no nests as of my info of 2007) and into California, and east in "colonies" to Colorado, with outposts in New Mexico and Arizona. Then the range appears again in central Mexico and Central America and on some of the Caribbean island. Are the three subspecies of Black Swift really subspecies, or species in their own right. No information.

Secondly, the Black Swift is notoriously FUSSY about its nest sites. An energetic, pioneering researcher in Colorado in mid century, Al Knorr, summarized the species' nest site requirements: a) the presence of water, and not just a pond or an alpine tarn, but usually a waterfall with a spray zone that keeps the nest site damp. In coastal California seepage around crevices in a sea cliff were acceptable as well b) high relief - in other words a site on a cliff or high on the vertical wall of a damp cave c) inaccessibility by predators. A nest on a rock shelf behind the outer spray zone of a waterfall is far less likely to be predated or even detected by some protein hungry predator d) unobstructed flyways and e) darkness.

These characteristics make to Black Swift's nest hard to find, but paradoxically, help reseachers develop   inventories of sites to search. Colorado reseachers have lead ther way for the past several decades in finding Black Swift colonies, although "colony" is a term used very loosely and may mean a site with only one nest. However, Black Swifts have a strong tendency to reuse old nests and many sites have been occupied for many years in a row.

Thirdly, and I personally find this the most fascinating of all the strange facts about this bird, Black Swifts lay a single egg. Of North American land birds, the only other species to lay a single egg is the Band-tailed Pigeon.

The swift's cousins, the Vaux's Swift and the White-throated Swift, both lay multi-egg clutches, but the Black Swift lays one. Its incubation period is very long, 23-26 days, a period common to species that hatch precocial young, like grouse, covered in feathers and almost ready to fly. However, in the case of the Black Swift, after 23-26 days, the chick is born naked and helpless. The young grow slowly and may slip into periods of tropor, an adaptation to long periods between feedings.

While the chick remains in the nest, it may be brooded by both parents at night. When it's older than 20 days, only one parent may stay with it during the dark hours. During the day the parents are generally away soaring around for their principal food, flying ants, which the parent bird binds with saliva into a bolus in its throat pouch. Californian young were fed twice a day.  Once over 30 days of age the chick was brought food only once, in the evening, but perhaps fed several times from the same bolus during the night.

The chick leaves the nest when it is about 44 days old, usually in early September. Once it leaves the nest, that's it. Nests are not revisited until it's time to nest again. The fledgling is presumed to join migratory flocks of adults.

I am deliberately omitting some information about the Black Swift which is quite as interesting as any of the facts herein. If I have whetted your appetite to learn more about the Black Swift, visit the American Birding Association's website to download Rick Levad's book, The Coolest Bird, A Natural History of the Black Swift and Those Who Have Pursued It. Try http//www.aba.org/thecollestbird.pdf