relatively little is known about the locations of North american landbirds’ winter roosts (Skutch 1989, Dobbs and martin 2000). North american Piciformes and cavity-nesting passerines have frequently been documented using cavities and variations thereof for overnight roosts during the non-nesting season, but relatively little is known about where passerines that nest in cups or other open structures spend the night (Skutch 1989, Dobbs and martin 2000, antczak 2010). Th rubycrowned Kinglet (Regulus calendula), an insectivorous cup-nesting species, has not been observed either nesting or roosting in cavities (Swanson et al. 2008). it breeds in coniferous forests in Canada, alaska, northern New England, and the western united States, and winters across western, mid-central, and southern North america south through mexico to Guatemala. in central California, the ruby-crowned Kinglet winters commonly (lepthien and Bock 1976, Swanson et al. 2008).