Barb,

I would vote for sun-realted feather care for the behavior you describe:

From Christopher Leahy's Birdwatcher's Companion to North American Birdlife, pp.773-774 (Princeton University Press, 2004).
"...main theories that have been advanced to explain sunbathing in birds are (1) that exposure to heat and light activates ectoparasites such as bird lice and perhaps drives them from area of the body that the bird has most trouble reaching and / or to areas where they can be captured most easily in the bill; (2) that the sun's ultraviolet rays release vitamin D from the preen oil, which in turn is ingested by the bird in the preening that typically follows a sunbath; (3) that the sun dries and fluffs the feathers by evaporating moisture and oil from the plumage (as may be true of dusting), thus maintaining good insulation; (4) that birds may be able to increase energy reserves by absorbing solar radiation directly through the skin (...); (5) that it feels good, especially when molting causes skin irritation; and, of course, (6) some optimal combination of 1 - 5."

The Cornell Lab of Ornithology Handbook of Bird Biology (published in association with Princeton University Press, Second Edition, 2004), Sandy Podulka, Ronald Rohrbaugh, Jr, and Rick Bonney, editors, p. 3- 22, lists some of the aforementioned and adds: "...conditioning the feathers by keeping them supple through limited heating,...".

The Cambridge Encyclopedia of Ornithology, Michael Brook and Tim Birkhead, editors, Cambridge University Press, 12991. p. 140. gets into the terminology (sunbathing not being an appropriate term since it does not share the same functions as true bathing) differentiating between sunning: behavior associated with feather care, and sun-exposure or sun-basking which is a mechanism to influence body temperature. The posture and "trance" you describe placing what you saw in the sunning category.

In contrast Olin Sewall Pettingill, Jr., in his 1985 fifth edition of Ornithology in laboratory and field, Academic Press, Inc., separates sunbathing (including an involuntary form after emerging from shade into sun), with fluffed and ruffled feathers, associated with feather care. This is associated with the risk of overheating and a retreat to shade afterwards. Sunning (including assuming a posture perpendicular to the sun with opened wings and tail), in contrast, appears associated with bodily warming, without subsequent retreat to shade.

I was taught that older published terminology has priority, so we should follow Pettingill's terminology. However I did not do a search of the primary publications referenced in these works (for lack of time, not curiosity), so I'll leave the decision what to call it up to you.

Cheers,
Martin Muller
martinmuller at msn.com


On 6/19,2010 Barb Deihl wrote:


Hello Tweeterpersons,

During the past 2 summers, I and others observed some behavior in a pair of Merlins, on the streets and rooftops of N. Seattle, that some called "anting" and others called "sunning". The reason given for the behavior was that it was an antiparasite strategy (the birds' scratching and time spent on a nest filled with growing young made it seem likely that they were indeed hosting some freeloaders).

An adult Merlin would, on a hot summer day, usually in the afternoon between 1 & 3 p.m., land on a south-facing roof edge (over the gutter), spread out it's wing- and tailfeathers and remain there for up to 5 minutes, fairly motionless. On one occasion, a Merlin landed on a gravel/grass driveway 10-15 ft away from 3 of us and stood there with spread feathers for what seemed to be less than a minute, turning slightly and walking slowly a bit before flying off. Photos taken by one of us, clearly show his positions.

As there was no sign of ants near the standing Merlin and no movement by the rooftop sunners such as there was in the blackbird anting video in the Bird Note segment Bob shared here, surely what we have witnessed is not anting, at least in the sense of gathering them up under the "tent" of wings & tail, to feed on. Merlins do not generally eat ants, as do robins and blackbirds, so any anting behavior seen in these birds, it seems to me, must relate to the ridding of parasites (through the application of formic acid to the feathers?). I am wondering if, this obvious sunning behavior we have observed with the Merlins, also in some way helps kill or otherwise reduce the number of parasites on them? And if so, how?

Any thoughts or references on any of this are most welcome.

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