Response of Great Blue Heron (Ardea herodias) Habitat Use to Changing Seasons and Tidal Levels Across a Grassland and Estuarine Ecosystem

The Great Blue Heron (Ardea herodias) is a generalist predator that forages from saltwater to grassy uplands. We sought to understand how tide and season influence heron habitat use throughout the estuarine and farmed grasslands of Fidalgo Bay and the adjacent Samish Flats in Skagit County, Washington, U.S.A. We counted 168 herons along 51 road transect surveys through both ecosystems across various tidal heights during the summer and winter (2023–2024). We subsequently applied negative binomial generalized linear models to the summer and winter datasets to examine the interaction between tidal height and location. In the summer, heron counts negatively correlated with tidal height in Fidalgo Bay, with fewer herons observed as tidal height increased. Herons did not forage in the bay in winter as daily tides were never low. Heron abundance in the Samish Flats was unrelated to tidal height in the adjacent marine environment. However, seasonality influenced heron counts, with more herons using the grasslands in the winter than summer. These findings contribute to a growing understanding of how abiotic factors may couple the use of marine and terrestrial environments by wading birds and highlight the importance of considering the juxtaposition of lands when planning for conservation.