DOI: 10.5061/dryad.k98sf7mht
title: Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2024

description: 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 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.
description: 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
 total. To estimate the number of breeding pairs, direct counts of attended
 nests were used. However, in some situation,s it was not possible to count
 breeding pairs or nests; in these cases, the number of individuals was
 used as a surrogate for breeding colony size. Each
 photo was counted by at least two counters. To generate an estimate of
 error, all counters conducted two complete passes of the same photo(s). A
 pass was defined as examining all areas thoroughly enough that any bird
 captured in the photo may be counted. To improve the accuracy and
 consistency of the counts, the total count from each counter was always
 within 10% of the other. If the count data resulted in differences larger
 than 10%, counters conducted a third pass or recounted until the average
 of both counts was within 10%. Once all images were counted, the peak
 count was determined for each colony and species by comparing total counts
 from each aerial survey.  Each species had a specific
 counting method. <strong>American white
 pelicans </strong> All individual American white
 pelicans that were visible on or near the breeding site were counted.
 Birds flying over the colony were not counted. Once chicks were large and
 mobile, no counts were made, and the photo(s) were recorded as “mobile
 chicks- not counted”. <strong>California gulls
 and Ring-billed gulls</strong>  All individual
 gulls that were visible on the colony were counted. Birds flying over the
 colony were not counted. The two gull species are not consistently
 distinguishable from aerial photos, therefore, California gulls and
 ring-billed gulls were grouped and counted together as the total numbers
 of breeding "gulls" at a colony. If chicks were large and
 mobile, no counts were made and the photo(s) were recorded as “mobile
 chicks- not counted”. <strong>Caspian
 terns </strong> Caspian terns were counted as
 either individuals or as attended nests, depending on the site. When
 counting individuals, all Caspian terns visible on the colony were
 counted. When counting attended nests, all Caspian terns sitting in nest
 scrapes were counted. If a pair was present at the nest scrape, only one
 of the birds was counted in an attended nest count. If chicks were large
 and mobile, no counts were made, and the photo(s) were recorded as “mobile
 chicks- not counted”. <strong>Double-crested
 cormorants and Brandt’s cormorants</strong> Early
 in the breeding season adults were sitting tight on nest structures making
 nest sites easier to identify, thus attended nests were counted. However,
 as the breeding season progresses and the number and size of chicks
 increases, the nest identity can be difficult to determine or be lost. If
 this was the case, then no counts were made and the photo(s) were recorded
 as “mobile chicks- not counted”. <strong>Great
 blue herons and great egrets</strong> Some
 double-crested cormorant breeding sites were within mixed species
 colonies; in these cases, great blue herons (<em>Ardea
 herodias</em>) and great egrets (<em>Ardea alba</em>)
 that attended nests were also counted.
description: # 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 three aerial surveys conducted on the 17th–18th May, 31st May–1st June, and 15th–19th June, 2024. These three survey counts were used to determine the peak colony sizes. ### Files and variables #### Files: 1. Data folder - Contains three Excel spreadsheets (**Survey1_Photo_Counts_0517-0518_2024.xlsx, Survey2_Photo_Counts_0531-0601_2024.xlsx, Survey3_Photo_Counts_0615-0619_2024.xlsx**) for each of the three aerial surveys conducted. Spread sheets contain the location and colony names, species counted, individual count estimates, final colony size estimates, and the reference for the corresponding photos which were counted. N/A's are present within the dataset when no count was made by one or both observer(s). If both observers did not count then N/A is also entered in the Average Count column. **Columns** Location = The general location name. Sub-location = The specific island/colony name. In cases where colonies were on channel markers within an estuary or bay, the sub-location gives the individual channel marker number within the location. Species = The species that was counted. AWPE = American white pelican, LAXX = California gulls and Ring-billed gulls (counted together), CATE = Caspian tern, DCCO = double-crested cormorant, BRAC = Brandt's cormorants, GBHE = Great Blue Heron, GREG = Great Egret. Count Type = Counts were either of number of individual birds or nests. See methods for further details and specific species methods.  Photo Date = The date (MM/DD/YY) the photo was taken. Observer_1_Count = The final count for the corresponding photo(s) from observer 1. Count units are either number of individuals or nest as defined by count type. Observer_1_Affiliation = Observer Affiliation. Observer_2_Count = The final count for the corresponding photo(s) from observer 2. Count units are either number of individuals or nest as defined by count type. Observer_2_Affiliation = Observer Affiliation. Average Count = The average of the two counters counts representing the final colony size estimate for that colony. Count units are either number of individuals or nest as defined by count type. Photo Used = Gives the name of the corresponding images which were used for the counts and the total number of photos used to complete a full colony count. **Arial Survey Images** Images are stored as supplementary information and publicly available on Zenodo ([https://doi.org/10.5281/zenodo.15103513)](https://doi.org/10.5281/zenodo.15103513 "Go to supplemental information") 1. **First Survey_0517_0518_2024** - This folder contains the photos from the first of three aerial surveys. The images included were used to determine colony size and relate to the corresponding count data from Survey1_Photo_Counts_0517-0518_2024.xlsx. Images are saved a .jpg files. 2. **Second_Survey_0531-0601_2024** - This folder contains the photos from the second of three aerial surveys. The images included were used to determine colony size and relate to the corresponding count data from Survey2_Photo_Counts_0501-0601_2024.xlsx. Images are saved a .jpg files. 3. **Third_Survey_0615-0619_2024** - This folder contains the photos from the third of three aerial surveys. The images included were used to determine colony size and relate to the corresponding count data from Survey3_Photo_Counts_0615-0619_2024.xlsx. Images are saved a .jpg files. Version changes: The changes to the dataset were minor, a few of the counts in the excel spreadsheets needed to be updated. I so replaced the excel spreadsheets with the new updated versions.  ## Code/software ### File Types: Software .xlm Files: Microsoft Excel  Zip Files: Unzip software, built in software on your operating system or installable software such as WinZip or 7-Zip JPG and TIFF files: Most standard image viewers, including Windows Photo Viewer on Windows, Preview on Mac, or third-party options like Adobe Photoshop, FastStone Image Viewer, ACDSee, or XnView