Climate variables are not the dominant predictor of Arctic shorebird distributions

1994–2018, with a majority of the sampling effort concentrated between 2003 and 2018. The Canadian Arctic was divided into 12 regions based on logistical considerations. Within each region plots were selected by random sampling, stratified by habitat. The proportion of plots in wet, moist and dry habitats varied by region depending on habitat abundance [see 29 for more details], but on average 16%, 29%, and 56% of plots were in wet, moist, and dry habitats respectively. In all years, surveys were conducted between June 18 and July 15. This corre- sponds with the latter part of shorebird courtship and the early part of incubation, when breed- ing territories could be identified from the birds’ territorial displays. Plots were typically 12–16 ha (400 m x 300–400 m). We excluded one set of surveys because extensive flooding led to very atypical breeding conditions. We also excluded surveys for which observers recorded nearby human development, which is rare across the study area and could potentially alter shorebird habitat preferences. For 211 plots that were visited in more than one year, we ran- domly selected one of the surveys to be included in the final dataset. Plots were surveyed for breeding birds following PRISM protocols [29]. Two surveyors searched the plot walking straight-line transects, covering a breadth of 50 m with the observers situated 25 m apart, using a GPS to ensure complete coverage of the entire plot. Surveys took approximately 90 mins. Observers recorded the number and species of all birds observed

within each plot. Altogether we observed 19 species of shorebirds, 17 of which were observed in at least 30 plots, our minimum threshold for developing habitat suitability models: Ameri- can Golden-Plover (Pluvialus dominica), Baird’s Sandpiper (Calidris bairdii), Black-bellied Plover (Pluvialis squatrola), Buff-breasted Sandpiper (Tryngites subruficollis), Dunlin (Calidris alpina), Least Sandpiper (Calidris minutilla), Pectoral Sandpiper (Calidris melanotos), Red Knot (Calidris cantus), Red Phalarope (Phalaropus fulicarius), Red-necked Phalarope (Phalar- opus lobatus), Ruddy Turnstone (Arenaria interpres), Sanderling (Calidris alba), Semipalmated Fig 2. Path diagram of the hypothesized relationships among predictors of shorebird occupancy. Groups of predictors with a blue label are included in climate-only models, and groups of predictors with an orange label are additional predictors included in climate +additional models. Arrows indicate direct causal paths between all combinations of variables in the respective groups are included in the path model of occupancy for each shorebird species. For example, the arrow from climate to land cover represents 60 arrows, one from each climate variable to each land cover variable. https://doi.org/10.1371/journal.pone.0285115.g002 PLOS ONE Climate variables are not the dominant predictor of Arctic shorebird distributions PLOS ONE | https://doi.org/10.1371/journal.pone.0285115 May 17, 2023 4 / 14