The Pygmy Nuthatch (Sitta pygmaea) and Mountain Chickadee (Parus gambeli) are two of the most abundant resident birds in yellow pine (Pinus ponderosa, P. jeffreyi) forests of western North America. Although nuthatches and chickadees usually forage in different ways, pygmaea has been characterized as “remarkably titlike in many of its foraging actions” (Norris 1958). In yellow pine woods, these two birds occupy what Sturman (1968) has called the “titmouse niche,” which might be more appropriately referred to as the titmouse “guild” (sensu Root 1967). This guild has been intensively studied in many parts of the northern hemisphere, primarily because its members are common, conspicuous and potentially important insect predators in temperate zone woodlands (Sturman 1968). In this paper, I focus on resource use patterns in relation to environmental structure, seasonal changes in resource distribution and interspecific flocking of the Pygmy Nuthatch and Mountain Chickadee.