Seabirds and Tides at Fine Temporal Scales

Abstract

Intricate tidal dynamics are the main drivers of ecosystem processes in coastal estuaries. Previous Pelagic Ecosystem Function studies have explored the relationship between tidal activity and seabird abundance in the San Juan Channel, Washington, but no strong or consistent temporal patterns were found. My objectives were to investigate: the fine scale temporal changes in bird abundance over the flooding tidal cycle; taxa specific responses to tides; and the influence of other environmental factors on variation among days and between years. I did this through sampling seabird abundance at half-hour intervals during the flooding tide on four consecutive days in the fall of 2013. Seabird abundance results showed consistent response to tidal phase for total birds and alcids in both 2013 and 2012. Variation between years suggested different foraging strategies were used by local gulls based on a change in feeding conditions. Additionally, the variation between years was related to large-scale oceanographic conditions, such as El Nino Southern Oscillation (ENSO). The differences in tidal response between taxa and between years suggests that fine temporal scale sampling can provide more insight into previously undetected factors affecting seabird abundance. Based on the results of this study, fine scale sampling can provide better predicting power and thus more informed decisions for management and conservation.