Assessing the abundance and movement of marine birds during a range of tidal currents at Cattle Point, San Juan Island

Abstract

Observational surveys are vital to ornithological studies. Often done by boat or plane, they can offer data on the behavior, ecology, and habitat use of marine birds. However, these methods can be challenging to use, expensive, and inaccessible. In this study, we propose a new shore-based method of surveying marine birds. We used a Fixed-Point Transect across Cattle Pass, San Juan Island, WA, a region with abundant bird populations and complex bathymetry. Over 6 days, we recorded the community composition, abundance and behavior of marine birds over all 8 tidal phases. We found that Gull and Cormorant abundance and behavior were likely not influenced by changes in tidal current speed in Cattle Pass. Alcid abundance, however, increased during fast flooding currents, with most birds either floating North with the current or flying South against it. These relationships can be explained by the preferred feeding habitats of these families: Gulls and Cormorants feed on larger prey in calmer, coastal waters, and Acids feed on aggregations or smaller prey in fast-moving, turbulent waters. The Fixed-Point Transect offers a widely accessible and applicable survey method to collect data on marine birds who often act as sentinel species in their environment. Observations of bird behavior and movement are important in furthering our understanding of the marine ecosystem to help inform marine conservation efforts in the face of climate change.