Dataset DOI: 10.5061/dryad.cc2fqz6nn

Associated publication

Feigin, S., T. Diehl, L. Niles, A. Dey, and J. Burger. 2026. “ Long-Term Population Trends and Spatial Redistribution of Shorebirds at a Critical Migratory Stopover.” Ecology and Evolution 16, no. 9: e74183. https://doi.org/10.1002/ece3.74183.

Contact

Stephanie Feigin — stephaniefeigin@gmail.com — Wildlife Restoration Partnerships, Greenwich, NJ, USA.

Overview

This dataset provides the annual peak counts and shoreline-use data underlying the analyses reported in the associated publication. It contains four decades (1986–2025) of standardized peak counts for four migratory shorebird species at their Delaware Bay spring stopover site (USA), together with paired counts partitioned by the New Jersey and Delaware shorelines for the two focal species (Red Knot and Ruddy Turnstone) and a supplementary shoreline breakdown for the two other species (Sanderling and Semipalmated Sandpiper) restricted to the period of complete species-specific coverage.

The dataset supports the log-linear population trend analyses (Table 4 and Figure 2 in the publication), the shoreline-use interaction model for Red Knots and Ruddy Turnstones (Table 5 and Figure 5), and the exploratory shoreline analyses for Sanderlings and Semipalmated Sandpipers reported in Appendix S2. An R script (reproduce_analyses.R) is provided to reproduce all reported statistical results from the CSV files.

Files

Data files

1. peak_counts_1986-2025.csv

Annual peak counts for four shorebird species at the Delaware Bay spring stopover, 1986–2025 (n = 40 years).

Missing values: Empty cells indicate years in which no reliable count was completed for that species. Red Knot and Ruddy Turnstone were counted every year (n = 40); Sanderling has n = 35 usable years; Semipalmated Sandpiper has n = 34.

Definition of "annual peak count": The maximum number of individuals of a given species observed on a single survey day during that year's spring stopover, from any survey type contributing to that year's monitoring. See publication Methods for the survey protocol and Data Limitations subsection for treatment of methodological changes over time.

2. shoreline_use_REKN_RUTU_1986-2025.csv

Peak count partitioned by shoreline for Red Knot and Ruddy Turnstone, 1986–2025.

Shoreline definition: The New Jersey shoreline includes all survey segments on the eastern (New Jersey) side of Delaware Bay, from Cape May Point north to the Cohansey River. The Delaware shoreline includes all survey segments on the western (Delaware) side, from Cape Henlopen north to the Smyrna River. The bay is partitioned by the deep-water channel that runs down the center of the bay. See Figure 1 of the publication for the study area map.

3. shoreline_use_SAND_SESA_1986-1996.csv

Peak-day shoreline counts for Sanderling and Semipalmated Sandpiper, restricted to the 1986–1996 period of complete species-specific coverage (n = 11 years). These data support the exploratory analyses reported in Appendix S2 of the publication.

Why 1986–1996 only: From 1997 onward, aerial observers periodically pooled unidentified small calidridine sandpipers into aggregate categories ("PEEP" and "MED/PEEP"), which may have included unknown proportions of Sanderling and Semipalmated Sandpiper. Species-specific shoreline totals after 1996 therefore underestimate true abundance by an unknown magnitude. From 2016 onward, aggregate categorization also affected Semipalmated Sandpipers directly. The 1986–1996 window is the only period with clean, species-specific, shoreline-level counts for both species (all PEEP and MED/PEEP counts zero throughout).

Definition of peak-day survey (this file only): Peak surveys were identified independently for each species based on that year's maximum bay-wide total, so the peak day for Sanderling may differ from the peak day for Semipalmated Sandpiper within a given year.

Analysis script

4. reproduce_analyses.R

A single R script that reads the three CSV files above and reproduces the log-linear population trends (Table 4), the shoreline-use interaction model (Table 5), and the exploratory shoreline trends for Sanderling and Semipalmated Sandpiper (Appendix S2). Expected values for every reported statistic are included as comments at the end of the script for verification.

Requirements

• R version 4.4.1 (R Core Team 2024). The script was tested under this version. Later 4.x versions should also work.
• Packages: none. The script uses base R functions only (lm(), summary(), read.csv(), AIC(), pf()). No installation of additional packages is required.

How to run

1. Download the three CSV files (peak_counts_1986-2025.csv, shoreline_use_REKN_RUTU_1986-2025.csv, shoreline_use_SAND_SESA_1986-1996.csv) and reproduce_analyses.R into a single folder.
2. Open R or RStudio and set the working directory to that folder, either with setwd("path/to/folder") in the console or, in RStudio, via Session → Set Working Directory → Choose Directory.
3. Run the script either by opening it in the R editor and running all lines, or by calling source("reproduce_analyses.R") from the R console.

The script writes all results to the R console; there are no output files to disk.

Survey methodology summary

Annual peak aerial surveys were conducted between the first week of May and the first week of June each year, coinciding with the spring shorebird stopover. Between 1986 and 2012 the surveys were conducted primarily from a fixed-wing aircraft flown approximately 30–60 m above ground level at approximately 110 km/h, following the shoreline at approximately 25–30 m seaward of the mean high tide line, with two observers counting shorebirds by species and one person recording GPS positions. From 2013 onwards, ground-based and boat-based counts at high-density locations (e.g., Mispillion Harbor, Egg Island) supplemented the aerial counts to improve counting accuracy in areas where aerial detection is most challenging. The peak counting window and survey timing relative to peak migration have remained consistent throughout the time series. Full methodological details, including the treatment of methodological changes over time, are provided in the Methods and Data Limitations subsections of the publication.

Data quality and limitations

• Peak counts represent a relative index of stopover-period abundance rather than absolute density; detection probability was not formally estimated. Aerial counts at Delaware Bay have been reported to underestimate the snapshot stopover population by approximately 17% relative to mark-resight estimates (Lyons et al. 2015), but this bias is consistent across years given the stable protocol.
• The addition of ground and boat counts in 2013 improved counting accuracy in high-density areas but did not alter the peak-detection window, which has remained the same since 1986. This transition is described in detail in the publication's Data Limitations subsection.
• Sanderling and Semipalmated Sandpiper have missing years in the annual peak count file reflecting periods when the aerial counter recorded medium-peep and peep aggregate categories without distinguishing between the two species, or when neither ground nor boat counters recorded these species independently. The shoreline breakdown file for these two species is further restricted to years with zero aggregate-category counts.

License

Creative Commons Zero (CC0 1.0). This dataset may be reused for any purpose without permission. Attribution to the associated publication is appreciated but not required.

Citation

Feigin, S., Burger, J., Diehl, T., Niles, L., & Dey, A. (2026). Data from: Long-term population trends and spatial redistribution of shorebirds at a critical migratory stopover. Dryad Digital Repository. https://doi.org/10.5061/dryad.cc2fqz6nn.