This species prefers mature forests and dim light. They probe the bark for spiders and other soft-bodied insects with their long, curved, tweezer-like bill. They use their stiff tail-feathers to hitch themselves up the tree trunks similar to woodpeckers and have independently evolved an unusual tail molt like that of woodpeckers, in which the central rectrices (tail feathers) are molted last instead of first as in most birds.
In the past this species was considered a race of the Treecreeper (C. familiaris) of Eurasia. However its song is more like that of the Short-toed Treecreeper (C. brachydactyla). Current thinking is that our bird is a separate species from either.
This is the race Certhia americana phillipsi which breeds in the Coast Ranges from San Francisco south to San Louis Obispo County. It is often (e.g. Clements 6th) synonomized with C. a. zelotes which breeds in the Cascades, Sierra and northern Coast Ranges, but differs from it in having a dark rather than white belly. The difference is evident here and this distinctive race is recognized by BNA.
Reference:
Unitt, P. and A. M. Rea. 1997. Taxonomy of the Brown Creeper in California. Pages 177-185 in The era of Allan R. Phillips. A Fest shrift. (Dickerman, R. W., Ed.) R. W. Dickerman, Albuquerque, NM.
Digiscoped with Panasonic DMC-LZ5 | Nikon FieldScope 3 | 30X WA | hand-held (no adapter)