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Feather lice transmission between seabirds

- PETER RYAN

ost seabirds breed on islands where they are safe from terrestrial predators - or at least they were until people started moving rats and cats and other commensal species around the planet. By breeding on islands, seabirds can occur at high densities, gaining social benefits from foraging together and sharing colony defence against avian predators such as skuas or gulls.

However, one drawback to having large numbers of birds breeding together in the same place year after year is that seabird colonies often accumulate high densities of parasites. Mostly this ancient conflict between host and parasite goes on unnoticed, but in the past few decades we have come to appreciate how internal parasites and diseases have major evolutionary implications for seabirds.

Ectoparasites are more readily detected - seabird biologists have a wealth of anecdotes about the challenges posed by ticks and fleas on seabird islands.

The brooding Cape Gannet (left bird) speckled with feather lice prepares to greet its mate, which lacks any visible lice. Seconds later, the partner also has lice on its feathers (right).