(Eurasian) Nuthatch
Sitta europaea

Nuthatches are adept climbers and can be seen hanging upside down from branches or descending head-first down tree trunks. This is a female - the males have darker red rumps and flanks.
 

(Eurasian) Nuthatch  (Eurasian) Nuthatch

1-2: Elfenau Nature Reserve, Bern, 12/05/2007.