Hooded Crows and koinophilia

Hooded Crows are far more sociable birds than Carrion Crows. Here in Rome we can see 300 of them in an evening in a single field, as they roost in safety.

Hooded Crows are the alternate version of the Carrion Crow. Hoodies are found in north and west Scotland, Ireland and the Isle of Man. Elsewhere, in the south and east of Scotland and in England, the Carrion Crow holds sway. Here in Rome, these must be the same Northern European Hooded Crow sub-species, Corvus cornix cornix, we get in the UK. Hooded Crows and Carrion Crows have an invisible ‘barrier line’ which runs between their populations and separates them from one another. That’s odd, because apart from their feathers and a tendency to be more sociable, they appear to be identical, even when you investigate their genes.

There must be something which keeps them from interbreeding, since they could, quite easily. The most commonly proposed idea for them keeping themselves apart is koinophilia – the tendency of animals to choose mates with fewer unusual or mutant features. Birds which exist on the borders and which encounter the other species frequently must have imprinted what a suitable mate would look like as a juvenile, as it doesn’t seem to matter how frequently they see the other species, there’s nothing doing. They could, of course, be put off by body language or language just as much as colouration, but that’s something not visible to us.

I’d love to get a closer view of them, as I’m sure there’s just a hint of pink in that grey. They’re so wary, having been so persecuted by humans, that even with a hide that’s going to be tricky.