Subspecies Limits and Geographic Patterns of Morphological Variation in California Gnatcatchers {Polioptila californica)

Abstract

California Gnatcatchers {Polioptila californica) are distributed from <br /><br />the arid coastal plain of southern California south throughout most of the lowland <br /><br />regions of Baja California. Atwood (1988) suggested that populations in central <br /><br />Baja California were not subspecifically distinct from populations occurring north <br /><br />of 30°N latitude, and that the range of the northern, nominate subspecies therefore <br /><br />extended south to the Cape region of the peninsula. However, re-examination of <br /><br />data used in the earlier analysis indicates that the primary break in patterns of <br /><br />morphological variation in California Gnatcatchers occurs near 30°N, and that <br /><br />populations north of this latitude are subspecifically distinguishable from popu- <br /><br />lations occurring in central Baja California. Patterns of variation south of 30°N <br /><br />latitude are less clearly defined, with variably distinct steps in clinal variation <br /><br />exhibited by different characters near 28°N and/or 24°N latitude. Multivariate <br /><br />analyses indicate that in central and southern Baja California the principal break <br /><br />in morphological variation occurs near 24° N latitude. Following these results, <br /><br />the naming and distributions of subspecies of Polioptila californica should revert <br /><br />to that initially proposed by Grinnell (1926): P. c. californica (north of 30°N), P. <br /><br />c. margaritae (from 30°N south to 24°N), and P. c. abbreviata (south of 24°N).