Distribution and demography of coastal Cactus Wrens ( Campylorhynchus brunneicapillus ) in San Diego County, California—2022 data summary

Abstract

We surveyed for coastal Cactus Wren ( Campylorhynchus brunneicapillus ) in 507 established plots in San Diego County in 2022, encompassing 4 genetic clusters (Otay, Lake Jennings, Sweetwater/Encanto, and San Pasqual). Two surveys were completed at each plot between March 1 and July 31. Cactus Wrens were detected in 214 plots (42 percent of plots). Cactus Wrens were detected in 31 percent of plots that have been consistently surveyed since 2020, indicating less plot occupancy than in 2021 (34 percent) and 2020 (35 percent). There were 202 Cactus Wren territories detected across all survey plots in 2022. In plots that have been consistently surveyed since 2020, we documented 94 territories, which is a decrease from 113 territories in 2021 and 109 in 2020. The number of territories declined from 2021 to 2022 in the Lake Jennings and Otay genetic clusters but remained virtually the same in the Sweetwater/Encanto genetic cluster. At least 78 percent of Cactus Wren territories were occupied by pairs, and 134 fledglings were observed in 2022. We observed 24 banded Cactus Wrens in 2022, 20 of which we could identify individually by band combination. Adults of known age ranged from 3 to at least 7 years old. All individually identifiable adult Cactus Wrens remained on the same territory in 2022 that they occupied in 2021, and we detected no movement of banded Cactus Wrens between genetic clusters. Vegetation at Cactus Wren survey plots was dominated by coastal sage scrub shrubs, such as California sagebrush ( Artemisia californica ), California buckwheat ( Eriogonum fasciculatum ), lemonadeberry ( Rhus integrifolia ), jojoba ( Simmondsia chinensis ), and San Diego sunflower ( Bahiopsis laciniata ). No definitive signs of fungal pathogens were observed on cactus within and around survey plots. Blue elderberry ( Sambucus nigra ssp. caerulea ) was detected at 39 percent of plots, 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 fewer dead cactus than plots that were not occupied by Cactus Wrens. Almost 80 percent of plots had more than 5 percent of cactus crowded or overtopped by vines and shrubs. Similar to 2020, Cactus Wrens occupied proportionally more plots with 5 percent or less of cactus crowded or overtopped by vines and shrubs, although this pattern was not observed in 2021. Non-native annual cover was less prevalent in survey plots in 2022 than in 2021, and Cactus Wrens did not preferentially occupy survey plots with 5 percent or less non-native annual cover than plots with more non-native cover.