HI:
FYI

--

Ian Paulsen
Bainbridge Island, WA, USA
A.K.A.: "Birdbooker"
"Rallidae all the way!"

---------- Forwarded message ----------
Date: Wed, 21 Sep 2005 18:29:06 -0700
From: Charles T. Collins <ccollins at csulb.edu>
To: lpatters at ix.netcom.com, birdbooker at zipcon.net
Cc: tweeters at u.washington.edu
Subject: Black Swifts

BLACK SWIFT STUFF 101

There were a couple of recent posting asking some questions about Black Swifts. Maybe I can add a few bits to the discussion. I'll try!

Black Swifts, as outlined in the account on Birdweb, is not nearly as well known as the other North American swifts. It is larger (almost twice the body of Vaux's Swifts at their fattest) and faster flying. Part of the problem is that it nests in remote places, almost exclusively behind waterfalls. And to top it off, the come in to the nest only once or twice a day, usually just at dusk. Those trying to document nest sites well know this and have to stay until after dark to make sure if Black Swifts are going to come in. Trying to find the nests is not reliable as they may be hidden from general view and only detected when a bird returns. They do tend to return to the same sites and very few are thought to be deserted from year to year. Getting one of the several books documenting the waterfalls of the state (Washington, Oregon and California) and going to some or all and waiting until dusk during mid-june until mid-august is the long and hard way, but nearly the only!
way of mapping their breeding distribution. The list of falls can be shortened a bit by omitting the "slide" falls and sticking to the ones with a vertical drop and room behind them or in the adjacent spray zone for nests.

Why do they nest there? Good question! Clearly it is safer from terrestrial predators and that may be the main reason. Not only Black Swifts but pretty much all of the members of that genus (Cypseloides) do this, with some of the smaller ones (Spot-fronted for instance) nesting in damp dark locations on a clif near but not behind a waterfall. This may relate to the size of the bird vs. the impact of the falling water even in peripheral spray that would hit them.

Why do they stay out so late? Probably because they specialize on swarming insects (particularly winged ants) and these may be available at dusk. They can specialize on these winged reproductive insects which are rich in stored fat by virtue of the fact that Black Swifts load up the esophagus with these insects rather than bringing one wad or bolus carried in the mouth as in most other swifts. The bolus carriers take a wide array of insects, of the size they can handle, including whatever is abundant and available. This includes insects of many orders and families. Accordingly, they can form a bolus of these insects glued together with saliva, in a relatively short period of time and thus come back to the nest to feed the nestlings several times an hour. Black Swifts spend more time looking for the patchy swarms of the lipid-rich insects as reproductive ants or termites and also cover more ground in the process. This would be inefficient if they had to head back with!
each mouthfull. Thus by stacking the equivalent of several boluses in the esophagus they can in fact go farther, stay away longer and bring back a larger load when they do. They have been observed regurgitating multiple mouthfulls to a chick on a dusk return and also photographed feeding multiple times during the night after roosting. This pattern or strategy does put some limits on how many chicks can be reared so they lay only a single egg clutch and only raise a single chick a year. Sounds like some long-lived seabirds doesn't it. The parallel has been noted by several workers. Banding studies (in progress) show that Black Swifts are long-lived; the current record is about 17 years but that is not likely to be a maximum.

Anyway a long life, low reproductive rate, a secure nesting (and roosting site) and a dietary specialist.....there you have it, a Black Swift.

Further questions welcomed

Charles T. Collns
Calif. State Univ., Long Beach
ccollins at csulb.edu