Nuthatch

The nuthatches are Sitta, a genus of small passerine birds in the family Sittidae. They live in the Northern Hemisphere.
They have large heads, short tails, and powerful bills and feet. Nuthatches advertise their territory with loud, simple songs. Most species have grey or bluish upperparts and a black eye stripe.
They live in forests, often pine coniferous forests, on higher land (montane forests). As usual in such places, insects, nuts and seeds are their food. Unlike other birds, nuthatches can run down trees head-first, and hang upside down. They can run down trees as fast as they climb up them.
Nuthatches use holes in trees for nests. This 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 defence 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 except in trees.
All nuthatches store food, especially seeds. They hide seeds in tree crevices, in the ground, under small stones, or behind bark flakes. These stores are remembered for as long as 30 days.
Most nuthatches do not migrate. They stay in the forest through the winter, where they roost in large flocks. These flocks can have over 100 nuthatches. Sometimes they include other forest birds, such as tits and woodpeckers.