The Effects of Climate Change on the Nesting Phenology of Three Shorebird Species in the United States

SIMPLE SUMMARY: Previous studies have shown how climate change can lead some bird species to alter the timing of their breeding and migration. To understand this better in shorebirds, we investigated if the nesting times of three shorebird species in the United States have fluctuated due to increases in temperature and precipitation at their breeding sites. We found that the laying dates of our species have become earlier and temperatures at our nest sites have significantly increased over time. Precipitation did not show a clear trend over time in our study, though previous studies indicate precipitation has been increasing in the U.S. While we were unable to find evidence that precipitation affects when our species begin laying eggs, one species, the Willet, had significantly earlier laying dates as temperatures during the breeding months increased. While another species showed this same trend, it was not significant, and the third species showed later laying dates as temperatures increased. Our results demonstrate that changes in climate affect species differently, warranting further study in this field. ABSTRACT: Previous research suggests that a frequent response of organisms to the ongoing climate crisis is the adjustment of their reproductive timing or breeding phenology. Shorebirds may be especially vulnerable to increasing temperatures and precipitation, as many are migratory and depend on coastal habitats for wintering and breeding. These particular habitats could be at risk due to changes in climate, and nesting times often depend on food availability, which is often directly influenced by temperature. We investigated if clutch initiation dates (CID) for three shorebird species in the United States have become earlier over time with increasing temperatures and precipitation. We used nest records from Cornell’s NestWatch program and various museum databases and weather station data from the National Oceanic and Atmospheric Administration. We found evidence that CIDs have become earlier over time, though this was only a significant factor for one species. While temperature in our study areas has increased significantly over time, precipitation changes were more variable and not always significantly predicted by time. We found evidence that one species may be responding to increasing temperatures by nesting earlier, but there was no support for our hypothesis that CID has changed due to changes in precipitation for any species. Results varied for each species, indicating the importance of further studies on shorebirds as the effects of climate change on their nesting phenology may not be fully realized and will likely depend on the species’ biology and distribution.