California Gnatcatcher (Polioptila californica)

Subspecies differentiation and range‐wide genetic structure are driven by climate in the California gnatcatcher, a flagship species for coastal sage scrub conservation

“…The California gnatcatcher was originally listed as threatened in southern California due to declines in populations linked to extensive loss and fragmentation of coastal sage scrub habitat (Atwood, 1993 ), with estimates of habitat loss between the 1940s and 1980s of 70%–90% (Westman, 1981 ). Habitat reduction was likely most severe in Los Angeles, San Bernardino, Ventura and Riverside Counties (Atwood & Bontrager, 2020 ). Similarly, habitat loss in northern Baja California may be contributing to, or reinforcing, the genetic differentiation apparent at the international border.…”

“…Similarly, habitat loss in northern Baja California may be contributing to, or reinforcing, the genetic differentiation apparent at the international border. As early as the 1990s loss of habitat due to agriculture, grazing, housing and urban development rendered connection between southern California and Baja populations tenuous (Atwood & Bontrager, 2020 ; USFWS, 1993 ). Anecdotally, aggregations of gnatcatchers are sparse in this region.…”

“…Euclidean distances and modified habitat cost distances among all individuals were calculated in ArcMap v. 10.4.1 using the Landscape Genetics Toolbox. Habitat loss in southern California and in northern Baja have been associated with reductions in occupancy and may impact connectivity (Atwood & Bontrager, 2020 ). We used the global human modification of terrestrial systems model, v. 1 (Kennedy et al, 2020 ) to estimate converted lands.…”

“…Because not all models were nested under the same hierarchy, we ranked models by log likelihoods, the fit of the model‐data plots, and whether parameters converged to determine the best fitting model. To scale our transformed empirical values, we used a mutation rate (2.3 x 10 −9 substitutions/site/generation) that was estimated for another small passerine (Smeds et al, 2016 ) and assumed a generation time of 1 year on the basis of published age structure and breeding activity records from two sites (Atwood & Bontrager, 2020 ). We also used δaδi to estimate the following summary statistics for the rangewide dataset and each grouping from our population structure analyses: Watterson's Theta (ϴ), Tajima's D, and the number of pairwise differences.…”

Distribution and abundance of Least Bell’s Vireos (Vireo bellii pusillus), Southwestern Willow Flycatchers (Empidonax traillii extimus), and Coastal California Gnatcatchers (Polioptila californica californica) at the Santa Fe Dam, Los Angeles County, California—2022 data summary

“…Fish and Wildlife Service, 2019a). Territorial males often sing or call from exposed perches (Atwood and Bontrager, 2020). Males select nest sites, usually just below 1 m above the ground, in plant species in proportion to their availability in the habitat, typically California sagebrush (Artemisia californica) or California buckwheat (Eriogonum fasciculatum).…”