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Dryad

2024 Pacific flyway region Caspian tern (Hydroprogne caspia) colony surveys – aerial photos and colony count data

Data files

Mar 18, 2025 version files 16.90 KB

Abstract

The 2024 Caspian tern (Hydroprogne caspia) minimum breeding population in the Pacific Flyway region was estimated by census of known active and historical colony sites. We collected survey data for 155 colony sites (c.a., 98%, 88%, and 93% of known active, historical, and potential colony sites, respectively), including 37 colonies that were confirmed to be active in 2024. This is the fourth population survey conducted under a monitoring strategy developed by the U.S. Fish and Wildlife Service in 2015 and undertaken every third year. As part of this effort, Oregon State University flew aerial surveys from fixed-wing aircraft to locate and photograph Caspian tern colonies in Washington, Oregon, California, Alaska, Nevada, and Utah. Oblique aerial photos were analyzed to estimate the number of nests at active colonies. Here we provide aerial photographs and count summaries for active colonies surveyed by Oregon State University in 2024. Additional colonies in the Columbia River Basin are archived in a separate dataset, “Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2024”, DOI: 10.5061/dryad.k98sf7mht.