0 the rock wren (salpinctes obsoletus) is a small songbird of the wren family native to south america and western north america .
1  it is the only species in the genus salpinctes .
2  adults are about 12 cm long .
3  they have grey-brown upperparts with small black and white spots and pale grey underparts with a light brown rump .
4  additional distinctive features include a light grey line over the eye , a long slightly decurved thin bill , a long barred tail and dark legs .
5  they actively hunt on the ground , around and under objects , probing with their bill as their extraction tool .
6  they mainly eat insects and spiders .
7  its song is a trill that becomes more varied during the nesting season .
8 these birds are permanent residents in the south of their range , but northern populations migrate to warmer areas from the central united states and southwest canada southwards .
9  they are occasional vagrants in the eastern united states .
10  during the breeding season , they move to dry , rocky locations , including canyons , from southwestern canada south to costa rica to build cup nests in a crevice or cavity , usually among rocks .
