Landbird monitoring 2020 annual report: Channel Islands National Park

Hall, Linnea; Larramendy, Peter; Lee, Lena; Little, Annie

doi:10.36967/2301088

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 in the park during every breeding season since 1993. In this report, we summarize data collected during the 2020 breeding season. Landbird monitoring was conducted between 1 April and 30 June 2020. Using distance-based sampling methods in a standardized protocol, birds were counted on 7 of 10 permanent line transects (70%) (2 of 3 on Santa Barbara Island, 1 of 1 on East Anacapa Island, and 4 of 5 on San Miguel Island). Two transects were not sampled in 2020 because of nesting California Brown Pelicans (Pelecanus occidentalis) on Santa Barbara Island (i.e., Canyons Transect) and reduced person hours and unfavorable winds on San Miguel Island (i.e., San Miguel Hill Transect). For point counts, 225 of 338 (67%) permanent stations were counted (i.e., 30 of 33 points on Santa Barbara Island, 8 of 8 on East Anacapa Island, 100 of 112 on Santa Cruz Island, 40 of 40 on San Miguel Island, and 47 of 145 on Santa Rosa Island). The 8 Prisoners’ Cove points were not counted in 2020. Three points were not counted on Santa Barbara Island due to nesting pelicans: these points and the transect were also not counted in 2016–2019 to avoid disturbing breeding pelicans. Other points (i.e., on east Santa Cruz Island and Santa Rosa Island) were not counted due in large part to the global COVID-19 pandemic. Traveling to and from the park was only granted to essential NPS staff for the majority of the landbird season. Fifty-one bird species were counted from points and transects across all of the islands in 2020; 39 of these are breeding species on the island. Parkwide, the 10 most commonly detected breeding landbirds in 2020 were, in descending order: Horned Lark, Spotted Towhee, Song Sparrow, White-crowned Sparrow, Western Meadowlark, Orange-crowned Warbler, Bewick’s Wren, Island Scrub-Jay, House Finch, and Common Raven. On East Anacapa Island, 26 landbird species have been counted since 1993; 5 species were counted in 2020. No new transient species were detected in 2020; 10 transient or visiting species (nonbreeding, native species recorded only once or twice during surveys) have been counted on the island overall since 1993. On Santa Barbara Island, 49 landbird species have been counted since 1993; 15 species were counted in 2020. The highest number of Horned Lark since 1993 were counted in 2020 (n = 451). Warbling Vireo was a new transient species counted in 2020 on Santa Barbara; 30 transient or visiting species have been counted on the island since 1993. On Santa Cruz Island, 74 landbird species have been counted since 2013; 34 species were counted in 2020. Bullock’s Oriole was a new transient species counted in 2020 on Santa Cruz; 21 transient or visiting species have been counted on this island since 2013. On San Miguel Island, 69 landbird species have been counted since 1993; 14 were counted in 2020. No transient species were counted in 2020; 34 transient or visiting species have been counted on the island since 1993. On Santa Rosa Island, 75 landbird species have been counted since 1994; 26 were detected in 2020. Rose-breasted Grosbeak was a new transient species counted in 2020 on Santa Rosa Island; 30 transient or visiting species have been counted on the island since 1994. Across all the 5 islands, 3 transient or visiting bird species were newly counted in 2020, for a total of 77 such species counted since NPS monitoring began on the islands. Nonnative and invasive birds were counted on only 1 of the 5 islands in 2020: 4 European Starlings on Santa Rosa Island. However, anecdotal sightings of nonnative species occurred much more frequently (i.e., outside of the point and transect counts), and were made on all islands except Anacapa in 2020. The highest numbers of nonnative species detections occurred on Santa Cruz Island, with 33 detections of Eurasian Collared Dove (primarily at the Main Ranch area in the Central Valley), 15 detections of Brown-headed Cowbird (primarily at Scorpion Harbor), and 15 detections of European Starling (primarily at the Main Ranch and Scorpion Harbor). House Sparrows were observed fewer times, but on all islands except Anacapa; cowbirds occurred on all islands except Anacapa and San Miguel; and Rock Pigeon occurred on Santa Barbara and Santa Cruz Islands. In 2020, despite the COVID-19 pandemic, 67% of all points and 77% of all transects were counted among the 5 islands. Santa Rosa received the lightest sampling of points (32%), due to the difficulty of getting observers onto the island. Even with diminished sampling, species richness (number of species) values fell in predictable patterns: richness was greatest on the larger islands (75 on Santa Rosa, 73 on Santa Cruz) and least on the smallest islands (26 on Anacapa, 48 on Santa Barbara). We continue to recommend that nonnative invasive species, such as European Starlings on Santa Rosa Island, be removed before their numbers become harder to manage. Also, because Distance analyses assist statistically with evaluations of trends, we continue to recommend that a trend analysis using program DISTANCE, or newer hierarchical distance analyses, should be used after the 2020 season to assess 5-year trends in breeding species’ numbers following the 2015 trend analysis conducted by Coonan and Dye (2016).

Landbird monitoring 2020 annual report: Channel Islands National Park

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