The Eurasian treecreeper (Certhia familiaris) is a mouse-like bird that does not perch on tree branches like most birds, preferring to hold on to the trunk instead, similarly to woodpeckers. It climbs up trees, starting from the base and working its way to the top, where it spreads its wings and drops to the roots of the next tree.
The Eurasian treecreeper feeds on spiders and insects living in crevices in the bark. It is easiest to distinguish by its shrill calls, the most audible of which is an emphatic srii-srii-srii. In late winter and early spring, you can also hear its clear and short song, which is similar in tone to that of the blue tit and somewhat reminiscent of the willow warbler: tii-tii-tii-tititititititi-tii-tii-tyit.
The Eurasian treecreeper typically nests in a tree stump split open by a storm or between the detached bark and trunk of a dead tree. The base of its nest is always supported by a layer of rough spruce needles to prevent it from sliding down. In Helsinki, the Eurasian treecreeper nests in all woodland areas where there are old and dead trees or trees felled by the wind.
Eurasian treecreeper, photo Jussi Helimäki.