Editor's Note: As originally published by BNA, this account combined Oak Titmouse and Juniper Titmouse into a single account because most of the work on which it was based considered the two species conspecific ("Plain Titmouse"). Systematic revision of the Plain Titmouse complex separated these species (see Systematics), which will be treated in separate accounts when this account is revised.
Oak and Juniper titmice are common residents of warm, dry woodlands in the western United States, extreme northern mainland Mexico, and northwestern and southern Baja California. Until recently, these taxa were regarded as a single species in the genus Parus: Plain Titmouse (Parus inornatus). A comprehensive analysis of geographic variation in the species complex (Cicero 1996), along with genetic evidence of relationships within the family (Sheldon et al. 1992, Slikas et al. 1996), has led to their reclassification as sibling species in the genus Baeolophus (American Ornithologists' Union 1997). Although similar in appearance, the 2 species are distinguished by a suite of morphologic, colorimetric, genetic, vocal, and ecologic traits (Cicero 1996). They are discussed here in a combined treatment, however, in order to describe and compare distinctive features of each species.
Whereas the Oak Titmouse is found primarily in oak or oak-pine (Quercus-Pinus) woodlands of the Pacific slope, the Juniper Titmouse inhabits juniper (Juniperus) and piñon-juniper woodlands of the intermountain region. Both species are sedentary, nest in natural or woodpecker-excavated cavities, and mate for life. Pair bonds form during the first year, and both sexes defend territories year-round. Thus, unlike many other parids, these titmice generally do not form winter flocks. Clutches typically contain 6¿7 unmarked eggs.
The diet is varied, and the birds are known to cache food. Both species are highly vocal, and individuals are most commonly recognized by their chatterlike calls which males and females utter throughout the year. Males may sing infrequently during the nonbreeding season, with singing intensity increasing toward spring. Vocalizations are directed primarily toward intraspecific defense of terri-tories.
Of the 2 species, the Oak Titmouse in California has been the subject of most studies of natural and life history information, including pairing, territoriality, survivorship, dispersal, molt, and nesting and foraging behavior (Price 1936, Dixon 1949, 1956, 1962, Davis et al. 1973, Block 1989). Physiologic studies, on the other hand, have concentrated on the Juniper Titmouse in Utah (Cooper 1997) and Arizona (Weathers and Greene 1998). Vocalizations and vocal behavior have been studied in both the Oak Titmouse in California (Dixon 1969) and the Juniper Titmouse in Arizona (Gaddis 1983, Johnson 1983, 1987a). Other studies involving both species have focused on behavioral or ecologic interactions with sympatric congeners in California (Dixon 1954) and Arizona (Dixon 1950, Gaddis 1987), respectively. For the future, studies that use a comparative approach to assess differences between these 2 species in aspects of the annual cycle, and in thermoregulation and energetics, should prove especially valuable.
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