21 April 2005

Falcons hunting pigeons: yet another demonstration of natural selection

An interesting study by Palleroni et al., published in today’s Nature1 shows that peregrine falcons (Falco peregrinus) are less likely to catch the feral pigeons with the so-called “wild” plumage, characterized by a white rump, than those with other plumage types. These results were based on observations of 1485 attacks on feral pigeons by five falcons in Davis, California. To confirm these results, the authors switched the rump feathers of a large number of wild and blue-barred (another plumage type) pigeons. After plumage transfer, the manipulated wild phenotype suffered predation at the same rate as the unmanipulated blue-barred type, whereas the manipulated blue-barred type had rates of predation as low as the unmanipulated wild type.

This paper reminded me of a recent study by Pole et al.,2 that demonstrated that in Zimbabwe, African wild dogs (Lycaon pictus) selectively prey on those individuals of impala (Aepycerus melampus) that are in poorer condition.

However, there is an interesting difference between the results of these two studies. In the Palleroni et al., study what determined the likelihood of a pigeon getting caught by a falcon was its plumage, regardless of its health; whereas, in the Pole et al., study it was the physical condition of an impala that dictated its chances of survival. In other words, sometimes even a very healthy animal may be more likely to get eaten if it has the wrong plumage, or the wrong fur color, or some display on its body that attracts the predators’ attention.

Another key point these studies reinforce is that survival is to some extent a matter of chance. The healthier or better camouflaged individuals are not guaranteed to survive; they only have better chances to do so.

1. Palleroni, A., Miller, C.T., Hauser, M., Marler, P. 2005. Predation: Prey plumage adaptation against falcon attack. Nature 434:973-974.
2. Pole, A., Gordon, I.J., Gorman, M.L. 2003, African wild dogs test the ‘survival of the fittest’ paradigm. Proc. R. Soc. Lond. B (Suppl.) (
Biology Letters) 270:S57.

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