Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2024

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), American white pelicans (Pelecanus erythrorhynchos), great blue herons (Ardea herodias), great egrets (Ardea alba) nesting in the Columbia River Basin, during the 2024 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. Colony size was reported as the number of birds on colony, and, in the case of terns a..., Three fixed-winged aerial surveys were conducted in 2024, on the 17th – 18th May, 31st May – 1st June, and 15th–19th June, to help identify all active nesting colonies of piscivorous waterbirds in the region. To estimate the size of waterbird colonies, aerial photos were taken at oblique angles using a Canon EOS 7D digital SLR camera with one of two image stabilizing lenses, Canon EF 70 - 200mm or Canon EF 100 - 400mm. The lens and camera settings used are included within the image metadata. Photos were taken through the open window of the plane during low-altitude flyovers, ~800 – 1,200 feet above the colonies. Aerial images were reviewed, and select images were imported to ArcGIS (ESRI ArcGIS Pro 3.30 and ArcMap 10.8.1, Redlands, CA) to be used for manual colony photo counts. Using ArcGIS, point shape files were created for each image or series of images, depending on colony size. Points were placed manually on either attended nests or individual birds and then summed to give the tota..., , # Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2024

Dataset DOI: [https://doi.org/10.5061/dryad.k98sf7mht](https://doi.org/10.5061/dryad.k98sf7mht)

## Description of the data and file structure

Evans, A.F., N. Banet, Q. Payton, A. Peck-Richardson, W. Kennerley, A.R. Piggott, R.A. Orben. 2025. Avian predation in the Columbia River Basin: 2024 Final Annual Report: Submitted to the Bonneville Power Administration, Portland, Oregon, and the Grant County Public Utility District/Priest Rapids Coordinating Committee, Ephrata, Washington.

This README file describes the data package for the nesting distribution and colony size of colonial waterbirds in the Columbia River Basin, 2024, which accompanies the above technical report.

Description:

This dataset consists of high resolution aerial images and corresponding individual species or nest counts of colonial waterbirds breeding in the Columbia River Basin in 2024. Date were collected during t...,