[TN-Bird] On the rump color of feral pigeons

From: "Charles P. Nicholson" <cpnichol@xxxxxxxxxxxxx>
To: "TN-Bird Listserve" <tn-bird@xxxxxxxxxxxxx>
Date: Mon, 2 May 2005 21:09:04 -0400
The April 21 edition of the scientific journal Nature (which is published in
the UK and similar in content to the US-published journal Science) has an
interesting article on the rump color of feral pigeons (a.k.a. rock
pigeons).  The authors show, through a combination of field observations and
experimental manipulations, that pigeons with white rumps are less
susceptible to predation by peregrine falcons than pigeons with darker
rumps.  Interestingly, and not surprisingly, the ancestral Eurasian stock of
the rock pigeon (known to pigeon fanciers as the "Blue-bar") is
predominantly gray with black bars on the wings and tail and a white rump.
Following is a summary of the article from the AAAS's ScienceNOW weekly
email.
20 April 2005 

A Tail of Survival
 
Preying peregrine falcons plunge through the sky at more than 250 miles per
hour, leveling out at the last minute to knock speeding pigeons out of the
air in an explosion of feathers. But the victim's feathers are rarely white.
A new study shows that pigeons with white rumps have a strong advantage over
their grey-butted brethren in avoiding death from above--perhaps because a
bright derriere distracts the pursuing bird.

As anyone who has watched a flock of pigeons in the park knows, the birds
come in several colors and patterns. This multitude of markings is
maintained because pigeons tend to choose mates with plumage unlike their
own. But after hearing a talk about the role of markings in predator
evasion, Alberto Palleroni, then a Ph.D. student in ecology at the
University of California, Davis, began taking notes on which pigeons were
attacked by falcons as they "commuted" past his lab between the university
and nearby feed lots.

Over seven years, Palleroni, now at Harvard, and colleagues recorded nearly
1500 adult falcon attacks on pigeon flocks near Davis, 40% of which resulted
in kills. Although white-rumped pigeons make up 20-25% of the pigeon
population, they represented only about 10% of falcon attacks and less than
2% of kills, the researchers report 21 April in Nature. The team then
captured more than 750 white and gray-rumped pigeons and swapped their hind
feathers using rubber cement. When the researchers released the pigeons,
Palleroni says, "the survivorship completely flipped."
The white rump may act as a distraction to a falcon, say the researchers,
providing a focal point for the falcon's attention and preventing it from
noticing when the pigeon drops one of its dark-colored wings and rolls out
of the peregrine's fight path. As once-endangered peregrine falcon
populations continue to increase [ScienceNOW 6 May, 1998], this selection
pressure may play a growing role on the pigeon population. It may have
already begun: Over the course of Palleroni's experiment, the number of
falcon attacks increased, as did the proportion of white-rumped pigeons in
the population relative to their gray-rumped peers.

The findings "suggest the pigeon has a really good reason for having a white
rear end," says Steven Lima, an ecologist who studies predator-prey
interactions at Indiana State University in Terre Haute. Lima hopes the
researchers will continue to follow the birds over successive generations to
see if the pigeon population continues to change under the falcon's
selection pressure. That, he says, would be "evolution in action." --JESSICA
MARSHALL

Chuck Nicholson
Norris, TN



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[TN-Bird] On the rump color of feral pigeons

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