Can birds cross

Biology: can birds reproduce across species boundaries?

Until now, biologists believed that partners of different species could not have procreative offspring. This dogma is now wavering

Apparently, yes, if there is a partner crisis. Outwardly, they can hardly be distinguished: Arctic terns and common terns both have a red beak, white plumage and red legs. Despite the different ways of life, the external differences are minimal. Even ornithologists find it difficult to tell the two species apart.

The birds themselves don't seem to be too particular about it either. It has long been suspected that the terns occasionally cheat with the other species. Scientists in the USA have now succeeded in providing genetic evidence for the first time. On Penikese Island, Carolyn Mostello of the Massachusetts Division of Fisheries & Wildlife observed a breeding pair made up of a male coastal tern and a female common tern.

Coastal terns and common terns mate more often than expected

From 2007 to 2014, the couple was able to raise nine chicks. The descendants are considered to be first generation hybrids. By chance, the researchers discovered that one of them returned to the island and mated with a female common tern there. This liaison produced three healthy chicks, second generation hybrids, which is unusual. Actually, species boundaries are drawn where two individuals cannot produce offspring capable of reproduction.

Here was proof to the contrary.

The researchers assume that the arctic terns on Penikese Island have little choice but to mate. Only a handful of their species face up to 2500 individuals of the other species. This is how a long-term marriage can turn from an affair. But there is also another explanation.

It is possible that the egg from which the male arctic tern hatched later got into the nest of the other species, and the young bird was minted there. This is not uncommon in mixed colonies. “Coast terns and common terns may mate more often than you think,” says Carolyn Mostello.