DOI: 10.5061/dryad.q573n5tqt
title: Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2023

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), 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.
description: Three fixed-winged aerial surveys were conducted in 2023, on the
 13th–15th May, 3rd–5th June, and 15th–16th 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 is 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 2020. ArcGIS
 Desktop: Release 10.8.1. Redlands, CA) or DotDotGoose (Ersts, P.J. Version
 1.7.0. American Museum of Natural History, Center for Biodiversity and
 Conservation) 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. In both programs, 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 situations 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 clearly 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”.
description: # Aerial photos and colony counts of nesting colonial waterbirds in the
 Columbia River Basin, 2023 Evans, A.F., K. Collis, N. Banet, Q. Payton, R.
 Kobernuss, N. Windels, A. Peck-Richardson, W. Kennerley, A.R. Piggott,
 R.A. Orben. 2023. Avian predation in the Columbia River Basin: 2023 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, 2023, 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 2023. Date
 were collected during three aerial surveys conducted on the 13th–15th May,
 3rd–5th June, and 15th–16th June, 2023. These three survey counts were
 used to determine the peak colony sizes. Files: 1. Data folder - Contains
 three Excel spreadsheets (Survey1_Photo_Counts_0513-0516_2023.xlsx,
 Survey2_Photo_Counts_0603-0605_2023.xlsx,
 Survey3_Photo_Counts_0615-0616_2023.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 under Observer_1_Count and
 Observer_2_Count 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. 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 Reference = 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. 2. First Survey_0514_0516_2023 - 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_0513-0516_2023.xlsx. Images are saved a .jpg
 files. 3. Second_Survey_0603-0605_2023 - 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_0603-0605_2023.xlsx. Images are saved a .jpg files.
 4. Third_Survey_0615-0616_2023 - 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_0615-0616_2023.xlsx. Images are saved a .jpg files.