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

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.