How a white feather can outfox a falcongeons
By Tim Radford, science editor,
Thursday April 21, 2005
aerial menace zooms in from behind, the feral pigeon does what a dove's got
to do - it shows the white feather and stands a better chance of getting
clean away, US scientists say.
Albert Palleroni of Harvard University and three
colleagues report in Nature today that they set out to solve the puzzle of
the white patch often found on the rump of the feral pigeon Columbia livia.
In seven years the researchers recorded 1,485 attacks by five adult
peregrine falcons on flocks of feral pigeons flying around Davis,
California. They also observed 309 attacks by juveniles. They made a note of
the plumage of the luckless target.
And they found that whether the peregrines were at the peak of their powers,
or still on a learning curve, the result was the same. Only one dead pigeon
in 50 had a set of white feathers on its rump.
The scientists reasoned that the white patch might be an evolutionary
adaptation that helped its inheritor to live longer and procreate more.
Falcons swoop with fearsome speed: the fastest have been clocked at 157
meters a second - around 320mph.
So they tested the idea by capturing 756 white-rumped and blue-grey pigeons
and swapping their plumage coloration. They then released the birds again,
and monitored the kill rate of three particular peregrines.
Those birds who could no longer show the white feather fell victim to
peregrine strike as often as the blue-colored pigeons, while the newly
whitened showed a much increased ability to survive.
No pigeon can out fly a falcon. They escape by aerobatics. The white patch
somehow distracts the peregrine.
The peregrine falcon almost disappeared from large areas of its range 40
years ago, but has slowly been making a comeback. As more falcons begin to
cull the pigeons in modern cities, the US scientists argue, an increasing
proportion of their prey will start to show the white feather.