Holly berries are edible to birds, but depending on the variety (either American or English) they may not be able to eat them until late in winter or even early spring. The berries have a hard surface and have to soften due to weather conditions to be available as food...
The starlings usually peck away at our holly berries, but since they're in profusion this year, I don't know whether it's a good sign or not. We've just got eh red berries on our trees, and they seem to be mainly untouched.