Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2023

In many situations, colonial waterbird colony size is best evaluated from
aerial photographs taken during the breeding season. This is typically the
case where colonies are not accessible or when it is not feasible to count
all birds or nests from ground locations or by boat. This dataset presents
high resolution aerial imagery and corresponding nest counts of Caspian
terns (Hydroprogne caspia), double-crested cormorants (Nannopterum
auritum), Brandt’s cormorants (Urile penicillatus), California gulls
(Larus californicus), ring-billed gulls (Larus delawarensis), and American
white pelicans (Pelecanus erythrorhynchos) nesting in the Columbia River
Basin, during the 2023 breeding season. Photos were taken from a
fixed-wing aircraft during peak nesting, and colony size was estimated by
digitizing photos and enumerating visible birds using ArcGIS and
DotDotGoose. Colony size was reported as the number of birds on colony,
and, in the case of terns and cormorants, the number of active breeding
pairs. These data are part of a wider project to evaluate the efficacy of
management actions to reduce the impacts of predation by piscivorous
colonial waterbirds on Endangered Species Act (ESA)- listed juvenile
salmonids (smolts; Oncorhynchus spp.) in the Columbia River Basin.