Description
The California Least tern (Sternula antillarum browni) is a small, migratory shorebird currently classified as endangered. Statewide numbers of breeding pairs and fledges have dropped since 2010 raising concern over the efficacy of management efforts. Understanding the habitat characteristics that influence nest placement and nest success is needed so that management efforts can be optimized. In this study I characterize fine-scale habitat features and describe their relationship to nest placement and nest success. My main objectives were to provide statistically-rigorous data on Least tern preferred nesting habitat and associated nest fate from a large number of colonies in order to provide evidence-based recommendations for management. The results of this study confirm that ground cover at a Least tern colony is predominantly sand/shell substrate with low to moderate cover of shortstature vegetation, litter and/or rock. The placement of nests differed from the surrounding habitat on a range of scales. Across colonies, nests are significantly more likely to be placed in large areas with a higher percent cover of sand/shell and lower cover of vegetation and litter, though not solely in areas of 100% sand/shell. Moreover, the exact location of the nest is significantly different from areas just a few meters away. Positive nest outcomes are significantly associated with areas of 80-89% sand/shell cover, suggesting that some heterogeneity in the landscape is beneficial to nest success. Unfortunately, the analysis of the relationship between nest placement and nest fate was hampered by low statistical power due to limited information about fate on hatchlings. The results of this study indicate that interactions between California Least tern and the environment happen on many scales and reveal a very fine-scale spatial pattern at nests.. This fine scale pattern needs to be understood and incorporated into management of California Least tern colonies.
