birding-aus

Wood-swallows - Do they soar?

To:
Subject: Wood-swallows - Do they soar?
From: brian fleming <>
Date: Mon, 20 Nov 2006 14:54:21 +1100
I recently said on 'Birding-aus' that 'Wood-swallows are the only soaring passerines". While I am quite certain from observation that they do soar, I have been wondering where I first saw this in print. After an extensive search of the thousand or so bird-books in the house (no exaggeration), I can say that I first found it in a work by E. Thomas Gilliard, Associate Curator of Birds, American Museum of Natural History - "Living Birds of the World" (Hamish Hamilton, London, 1958). Just because it's an older book does not mean that it doesn't contain useful information. On p. 303, he writes: "The finest of passerine fliers, and excepting the ravens the only songbirds known to soar, are the wood-swallows.... When hunting, wood-swallows often soar high into the air on rigid wings. At such times they resemble miniature vultures. Their food consists entirely of insects captured in the air." [We now know that they also take nectar with brushlike tongues, and very surprised I was when I first saw them doing so in a flowering Ironbark at Cocoparra.]

The early 1980 edition of Graham Pizzey's Collins FG (the one with Ray Doyle's illustrations) gave more room for description: "On the wing their silhouette is rather like the Common Starling; the flight is graceful and absolutely diagnostic: quick shallow wingbeats, circling glides and soaring on shapely pointed wings and spread tails; but pursuing flight can be dashing." (p.392).

Current edition, (1997) ill. Frank Knight, P., in the Family Introductions section, p 542: "Unrelated to true swallows, woodswallows are graceful songbirds with broad, pointed wings; they are among the few songbirds that soar."

And what is soaring flight anyway? Pizzey's definition (p. 551) is "rising flight on still, extended wings, using thermals or updraughts to gain height without flapping". It is typically seen in broad-winged birds such as large raptors, storks, pelicans etc - I recall resting during a mountain hike, flat on my back, while we watched a Brown Goshawk circling up in a thermal, never moving its wings until lost to human sight. I understand that in Africa small vultures such as the Egyptian can get airborne much earlier in the day than the very large heavy species, enabling them to get a start on small and part-eaten carcasses before the big ones arrive and bully them off. The 'dynamic soaring' utilized by albatrosses over waves, is a different action and requires a long, narrow wing (high aspect-ratio).

Swallows have very narrow wings and cannot soar, though of course they can and do glide between burst of flapping. I don't really know whether Needletail Swifts soar, though their powers of flight are prodigious. Half their weight is breast muscles, according to the books. Can they gain height without too much effort by using the updraughts in the thunderstorms which often seem to bring them?
Anthea Fleming
in Melbourne


===============================
www.birding-aus.org
birding-aus.blogspot.com

To unsubscribe from this mailing list, send the message: unsubscribe (in the body of the message, with no Subject line)
to: 
===============================

<Prev in Thread] Current Thread [Next in Thread>
Admin

The University of NSW School of Computer and Engineering takes no responsibility for the contents of this archive. It is purely a compilation of material sent by many people to the birding-aus mailing list. It has not been checked for accuracy nor its content verified in any way. If you wish to get material removed from the archive or have other queries about the archive e-mail Andrew Taylor at this address: andrewt@cse.unsw.EDU.AU