FORAGING BEHAVIOR AND NESTLING DIET OF CHESTNUT-BACKED CHICKADEES IN MONTEREY PINE

The foraging behavior and nestling diet of Chestnut-backed Chickadees (Parus rufescens) was studied during the breeding season (March-May) i n a Monterey pine (Pinus radiata) plantation, 1991-1992. Adult birds s pent 79% (+/-7.1 SD) of their foraging time on Monterey pine as a resu lt of prey availability. The majority of this time was spent perch gle aning and hang gleaning prey from the outer needles of the upper tree crown. Nestling diet was composed of approximately 43% Monterey pine s awfly larvae (Acantholyda burkei, Hymenoptera: Pamphiliidae) and 17% t ree camel crickets (Gammarotettix bilobatus, Orthoptera: Ehaphidophori dae). Both insects feed upon Monterey pine foliage. Spiders and indivi dual Homoptera, Hemiptera, Coleoptera, Lepidoptera, and Diptera specie s comprised the remaining 40% of the diet. Monterey pine serves as an important foraging resource for Chestnut-backed Chickadees during the breeding season and may have contributed to the range expansion and po pulation increase of this species in the San Francisco Bay region.