Effects of Time, Tide, and Currents on Pacific Great Blue Heron (Ardea Herodias fannini) Abundance, Behavior, Prey, and Strike Rates at False Bay, San Juan Island

Abstract

Pacific Great Blue Herons (Ardea herodias fannini) are large, non-migratory wading birds residing on the coast of Washington State, British Columbia, and Alaska. Herons are commonly found near shores of wetlands and tideflats, feeding primarily on small fish. Although pre-existing studies have looked at the individual effects of either tide, time, or current on herons, we aimed to compare the effects across all of these components on abundance, behavior, prey, and strike rate and how they differ in their correlations. We conducted continuous and opportunistic field surveys between August 7 and August 12 at False Bay on San Juan Island and found the abundance of herons was highest while located in the water during mornings and low tide, whereas a smaller group of herons were roosting in the afternoon and at high tides. Additionally, herons in the water spent a majority of the observation period hunting, with attempted and successful strike rates highest at low tides and ebb currents. We found prey size and handling time were directly proportional. Our data showed current impacted the size and type of prey caught. We recommend that future studies extend our methods to a broader range of tides and times of day, as well as to other sites and times of year to attain a more holistic understanding of factors that influence the natural history of herons.