How a White Feather Can Outfox a Falcon

When 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 metres 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-coloured pigeons, while the newly whitened showed a much increased ability to survive.

No pigeon can outfly 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.