Looking something akin to a small, tree-surfing kingfisher or a tiny woodpecker, the acrobatic Nuthatch (Sitta europaea) will scoot up and down the bark head first, in a manner unlike any other bird. Certainly it doesn’t creep endlessly upwards like the Treecreeper.
The Nuthatch will pluck small insects and grubs from the bark of trees for food, but will also find seeds and kernels and wedge them in a crevice smashing them open with its beak, hence the hatching of nuts from whence its name originates. It has a variety of calls from a pew, pew, pew to a pwee pwee, by way of a ka-ka-ka.
You will see them on garden bird feeders and often hanging around the visitor centres of nature reserves, anywhere with an abundance of insect life, decent craggy-barked trees, and a seed supply.