Ball 12. The Truthiness of Animal Signals

Another one from the bird files:


The natural world has no equivalent of the Federal Trade Commission to monitor truth in advertising. Boasts about reproductive fitness—elaborate plumage, antlers and other ornaments—must be sincere because the physical costs of producing gaudy displays are so high. Animals with the most impressive finery have the physical robustness necessary to develop the flourish while fighting environmental threats like predators and infections.

Biologist Gary Bortolotti, of the University of Saskatchewan, says:

Signals have to be honest or cheat-proof and it is their cost that prevents cheating. Peahens like peacocks with big trains. Only the best quality males can pay the price and grow a big train. If it were cheap every male would grow one.

(See Ball 11. Begging to Differ)

As intuitive as it seems, however, proving the honesty of ornamentation is tricky. But Bortolotti and his colleagues have found compelling new evidence that, at least for one species of game bird, the cocks of the walk really strut the talk

The study found that the size (and, presumably, the attractiveness to females) of decorative combs above the eyes of red grouse depend largely on how much recent environmental pressure the birds endured. In particular, the researchers showed that levels in the birds’ feathers of the stress hormone corticosterone were linked to the height of their crimson courtship tufts. What’s more, the study also found that infecting the grouse with parasites diminished the size of the ornamental plumage—consistent with the idea that the wage of cultivating displays is reduced immunity.

We all know too well the important role of stress is in our own lives. How well an animal copes with the many, often concurrent, challenges in the environment may be one of the more meaningful, if not the best, overall measure of its ‘quality’ and fitness potential.

The researchers reported their findings in PLoS ONE.