DOI: 10.5061/dryad.kprr4xhgh
title: 2024 Pacific flyway region Caspian tern (Hydroprogne caspia) colony surveys – aerial photos and colony count data

description: 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.
description: In 2024, we attempted to collect colony size estimates from all
 known active, historical, and potential colony locations in the Pacific
 Flyway region, and for any new colony sites identified during our census
 effort. Surveys of all colony sites were targeted to capture the peak
 colony attendance, based on regional and site-specific nesting
 chronologies from previous years. Numbers of attended nests were
 quantified using different methods depending on colony location,
 accessibility, collaborator availability, and independent ongoing research
 or monitoring efforts. These methods included fixed-wing aerial surveys,
 UAV surveys, boat surveys, and ground visits. Aerial photography of active
 colonies was obtained whenever possible, which allowed researchers to
 efficiently observe colonies across large geographic regions during a
 short window during peak nesting. Aerial surveys provided high resolution
 oblique photography (Canon DSLR and mirrorless cameras with 100-600 mm
 equivalent zoom lenses) taken while flying over colonies at low altitude
 (ca. 500 – 1200 feet AGL). For larger colonies, multiple images were
 stitched together into high-resolution files using Adobe Photoshop
 (Version 25.1; San Jose, CA). When possible, these stacked images were
 captured in rapid succession using 12 fps bursts to avoid artifacts from
 perspective shifts (parallax) due to photographing from a moving aircraft
 platform and to eliminate double counting birds in flight. Ground based
 photos were used when provided by collaborators, and if aerial photography
 was not possible. Photography of each active colony was analyzed by two
 independent observers using either ArcGIS Pro (Version 3.3; ESRI,
 Redlands, CA) or DotDotGoose (Version 1.7.0; Ersts 2024) to enumerate
 nests and loafing adult terns. Counts were finalized when count totals
 were within 10% (calculated by dividing the difference between the two
 counts by the mean of the two counts). This imagery was funded by the
 Bureau of Reclamation (Reclamation), US. Department of Interior. Funding
 was provided by Reclamation as part of its mission to manage, develop, and
 protect water and related resources in an environmentally and economically
 sound manner in the interest of the American public. Funding was provided
 through Grant R23AP00195. The views in this report are the author's
 and do not necessarily represent the views of Reclamation.
description: # 2024 Pacific flyway region Caspian tern (Hydroprogne caspia) colony
 surveys – aerial photos and colony count data
 [https://doi.org/10.5061/dryad.kprr4xhgh](https://doi.org/10.5061/dryad.kprr4xhgh) ## Description of the data and file structure This README file describes the data package for 2024 Pacific Flyway Region Caspian tern (Hydroprogne caspia) colony surveys – Aerial photos and colony count data Description: This dataset consists of high-resolution aerial images and corresponding nest counts of Caspian Terns (*Hydroprogne caspia*) colonies surveyed during the 2024 Pacific flyway population census.  Methods used to collect colony images included fixed-wing aerial surveys, UAV surveys, boat surveys, and ground visits. ### Files and variables #### File: 2024\_CATE\_Aerial\_Survey\_Counts\_Archive.xlsx Files: Data folder -Contains an Excel spreadsheet (2024_CATE_Aerial_Survey_Counts_Archive.xlsx) The spread sheet contains colony names, location, including latitude and longitude, 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 C1_Chicks and C2_chicks 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 Mean_Chicks  **Variables** Colony_Name = The assigned colony name. State = The US state in which the colony is located. Region = The general region of the colony within the US state. Lattitude = Colony latitude. Longitude = Colony longitude. Counter_1 = Counter 1 four letter name code C1_Affiliation = Counter 1 affiliation. C1_Nest = Total number of nests counted by counter 1. C1_Stand = Total number of standing birds counted by counter 1. C1_Chick = Total number of chicks counted by counter 1. Counter_2 = Counter 2 four letter name code. C2_Affiliation = Counter 2 affiliation. C2_Nest = Total number of nests counted by counter 2. C2_Stand = Total number of standing birds counted by counter 2. C2_Chick = Total number of chicks counted by counter 2. Mean_Nest = The mean of counter 1 and counter 2 nest counts, representing the final total nest estimate. Mean_Stand = The mean of counter 1 and counter 2 stand counts, representing the total stand estimate. Mean_Adults = The mean of counter 1 and counter 2 combined standing bird and nest counts, representing the total adult estimate. Mean_Chicks = The mean of counter 1 and counter 2 chick counts, representing the total chick estimate. Survey_Date = Date of the survey (MM/DD/YY). Survey_Type = The survey type used, one of three options, aerial fixed wing, aerial UAV, or ground survey. Photos_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. #### 2.  Zip-folder - \*\*contains archived photos (CATE\_2024\_Photo\_Archive.zip). This file contains the photos from aerial surveys of Caspian tern colonies. The images included were used to determine number of adults and nests and relate to the corresponding count data from 2024_CATE_Aerial_Survey_Counts_Archive.xlsx. Images are saved a .jpg and .tiff files. 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 ## Access information Other publicly accessible locations of the data: * Population estimates can also be publicly found in the BPA annual reports;  [https://www.birdresearchnw.org/project-info/publications-&-reports/unpublished-reports/](https://www.birdresearchnw.org/project-info/publications-&-reports/unpublished-reports/)  * Aerial photos and colony counts of nesting colonial waterbirds in the Columbia River Basin, 2024”, DOI: 10.5061/dryad.k98sf7mht.