Distribution and demography of coastal Cactus Wrens (Campylorhynchus brunneicapillus) in southern San Diego County, California — 2021 Data summary

Abstract

We surveyed for coastal Cactus Wren ( Campylorhynchus brunneicapillus ) in 378 established plots in southern San Diego County in 2021, encompassing 3 genetic clusters (Otay, Lake Jennings, and Sweetwater/Encanto). Two surveys were completed at each plot between March 1 and July 31. Cactus Wrens were detected in 130 plots (34 percent of plots), remaining virtually the same as the percentage of plots occupied in 2020 (35 percent). There were 113 Cactus Wren territories detected across all survey plots in 2021, an increase from 109 in 2020. At least 86 percent of Cactus Wren territories were occupied by pairs, and 50 fledglings were observed in 2021. We observed 48 color-banded Cactus Wrens in 2021, 44 of which we could identify to individual. Adults of known age ranged from 2 to at least 7 years old. Adult Cactus Wrens moved, on average, 0.1 kilometers (maximum 0.5 kilometers) from their 2020 territories to their 2021 territories. No known-identity Cactus Wrens moved between genetic clusters from 2020 to 2021. Vegetation at Cactus Wren plots typically was dominated by coastal sage scrub shrubs, such as California sagebrush ( Artemisia californica ), California buckwheat ( Eriogonum fasciculatum ), lemonadeberry ( Rhus integrifolia ), and San Diego sunflower ( Bahiopsis laciniata ). Twenty-nine percent of plots contained blue elderberry ( Sambucus nigra ssp. caerulea ), and Cactus Wrens occupied proportionally more plots with elderberry than plots without elderberry. Very little dead or unhealthy cactus was observed within all survey plots, and the plots that were occupied by Cactus Wrens were likely to contain more healthy cactus than plots that were not occupied by Cactus Wrens. Thirteen percent of plots had 5 percent or less of the cactus crowded or overtopped by vines and shrubs. Although in 2020, Cactus Wrens occupied proportionally more plots with 5 percent or less of cactus crowded or overtopped by vines and shrubs, this pattern was not found in 2021. Non-native annual cover was 5 percent or less at 29 percent of plots and, unlike in 2020, Cactus Wrens appeared to occupy proportionally more plots with less non-native annual cover than plots with more than 5-percent annual cover.