Landbird trends 2016–2021, and 2021 annual report: Channel Islands National Park

Larramendy, Peter; Hall, Linnea; Little, Annie

doi:10.36967/2299629

The National Park Service (NPS) began monitoring landbirds at Channel Islands National Park in 1993 as part of its long-term inventory and monitoring program. The park’s landbird monitoring later became part of the NPS Inventory and Monitoring Division’s Mediterranean Coast Network long-term monitoring programs. Consequently, landbird monitoring has been conducted during every breeding season since 1993. In this report, we summarize data collected during the 2021 breeding season and we analyze trends in a select number of species. Landbird monitoring was conducted between 10 March and 22 May 2021. Using distance-based sampling methods in a standardized protocol, birds were counted on 334 of 338 permanent point count stations (99%) across the Channel Islands monitored for landbirds. These surveys were conducted at 29 of 33 points on Santa Barbara Island, 8 of 8 on East Anacapa Islet, 112 of 112 on Santa Cruz Island, 40 of 40 on San Miguel Island, and 145 of 145 on Santa Rosa Island. Four points on Santa Barbara Island were not counted due to nesting California Brown Pelicans (Pelecanus occidentalis) and Western Gulls (Larus occidentalis); 3 of 4 points (i.e., 17, 19, and 20) were also not counted in 2016–2021 to avoid disturbing breeding pelicans. This was the first monitoring season that the permanent line transects on Santa Barbara, East Anacapa, and San Miguel Islands were not surveyed. During the 2021 monitoring season, Channel Islands National Park decided to stop using line transects and focus on point count stations only, based on an external review of the landbird monitoring program. Fifty-six bird species were counted at point count stations across all of the islands in 2021. Parkwide, 40 of these species are breeders in Channel Islands National Park. Parkwide, the 10 most detected breeding landbirds in 2021 were, in descending order: Spotted Towhee, Song Sparrow, Bewick’s Wren, Orange-crowned Warbler, House Finch, Western Meadowlark, Horned Lark, Common Raven, Island Scrub-Jay, and Pacific-slope Flycatcher (scientific names in Table 2 and Appendix A). On East Anacapa Islet, 26 landbird species have been counted since 1993; 7 species were counted in 2021. No new transient species were detected in 2021; 6 transient or visiting species have been counted on the island overall since 1993. On Santa Barbara Island, 50 landbird species have been counted since 1993; 13 species were counted in 2021. Lincoln’s Sparrow was a new transient species counted in 2021 on Santa Barbara; 23 transient or visiting species have been counted on the island since 1993. On Santa Cruz Island, 78 landbird species have been counted since 2013; 45 species were counted in 2021. Hermit Warbler, Lawrence’s Goldfinch and Warbling Vireo were new transient species counted in 2021 on Santa Cruz Island; 21 transient or visiting species have been counted on this island since 2013. On San Miguel Island, 70 landbird species have been counted since 1993; 10 were counted in 2021. No transient species were counted in 2021; 32 transient or visiting species have been counted on the island since 1993. On Santa Rosa Island, 78 landbird species have been counted since 1994; 39 were detected in 2021. No new transient species were counted in 2021 on Santa Rosa; 21 transient or visiting species have been counted on the island since 1994. Nonnative and invasive birds were counted on only 1 of the 5 islands in 2021: 23 European Starlings on Santa Rosa Island. However, anecdotal sightings of nonnative species occurred more frequently (i.e., outside of survey times) on Santa Cruz and Santa Rosa Islands in 2021. The highest numbers of nonnative species detections occurred on Santa Rosa Island, with 25 detections of Eurasian Collared Dove (primarily at the Historic Ranch), 18 detections of European Starling (Historic Ranch), 2 detections of Brown-headed Cowbird, and 1 Rock Pigeon detection (Historic Ranch). Other species were not reported by Channel Islands National Park landbird monitors or in eBird in 2021. This was the first annual monitoring report since the Coonan and Dye (2016) trend report to incorporate density estimates for particular species across Channel Islands National Park. Parkwide, 13 species were analyzed using the Distance Package in R. Of the 13 species analyzed, 5 had either increasing or decreasing densities from 2016 to 2021. All park islands except for Santa Barbara had a species that showed an increasing or decreasing trend from 2016 to 2021. Horned Lark and House Finch on San Miguel Island were the only species to show decreasing trends from 2016 to 2021, which is opposite from the trend presented by Coonan and Dye (2016).

Landbird trends 2016–2021, and 2021 annual report: Channel Islands National Park

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