Nuthatch
Nuthatches use holes in trees for nests. This also means they compete with squirrels and woodpeckers for these holes. In fact both squirrels and the great spotted woodpecker kill nuthatches if they can. Owls and hawks also kill these small birds, but that is not to do with their nest-holes. In defense of their nests, nuthatches make the entrances smaller by packing the edges with mud or tree resin. Predation is not really a threat, just a fact of life for them. Loss of coniferous forest in some countries is a threat. They cannot live in anything else except in trees.