The california least tern (sternula antillarum browni hereafter clte ), a federally endangered seabird that nests during the summer months on beaches between central california and the baja california…

The U.S. Fish and Wildlife Service, under the Cooperative Endangered Species Conservation Fund (CFDA 15.615), awarded a $330,628 project grant to the California Department of Fish and Wildlife (CDFW) to study the drivers of reproductive success for the federally endangered California least tern. The 3-year project, running from Sep 1, 2024 to Aug 31, 2027, will leverage existing and new empirical data on oceanographic conditions, tern diet, nest attendance, predation, and reproductive output from three key breeding sites in California. The research will use structural equation modeling to identify the key factors directly and indirectly influencing the tern's poor reproductive success, which has prevented population recovery despite ongoing management efforts. The results are anticipated to be applicable across much of the tern's range and will guide future conservation and management actions for this endangered seabird species.

The california least tern (sternula antillarum browni hereafter clte ), a federally endangered seabird that nests during the summer months on beaches between central california and the baja california peninsula in mexico, has experienced a steady population decline since 2009. This decline has been attributed to observed low reproductive success, despite widespread implementation of site management interventions such as site protection (e.g., fencing, signage), predator control, and habitat restoration. This suggests that population recovery and recruitment could be influenced not only by site-specific variables, but also by larger-scale environmental factors such as changes in ocean conditions which influence fish distributions, abundance, and availability. Fish population declines or shifts due to changes in oceanic conditions, such as sea surface temperatures (SST), may lead to indirect effects on adult nest attendance or nest provisioning if breeding adults are forced to either fly further from the colony to forage or settle for less nutrient-rich prey species, which can also have direct negative impacts on reproductive success. This research leverages contemporary and archived empirical data to identify the key drivers of clte reproductive output. Existing data on oceanographic conditions, clte diet, nest attendance, predation events, and reproductive success from marine corps base camp pendleton (mcbcp), batiquitos lagoon ecological reserve (bler), and naval base coronado (NBC) will be supplemented by additional EGG and fecal sampling as part of this proposal and analyzed to characterize the relationship between these variables. Relationships among the variables of interest will be analyzed using a multivariate statistical technique known as structural equation modeling (SEM), which will enable US to test multiple competing hypotheses and identify which variables are most strongly influencing reproductive success. This analysis was identified as a primary recommended action in the 2020 5-year review and understanding these factors and how they directly and indirectly influence clte reproductive output is the critical next step to effectively support and promote successful population recovery. The three sites included in this study represent nearly 50 of the clte population statewide, thus the results are anticipated to be applicable to much of the species range and will be used to effectively direct management effort and funding moving forward. This project provides actions and assessments that are critically needed for the conservation and recovery of a federally- and california state-listed species as outlined in the clte recovery plan and 5-year review and must be completed if we expect to address the poor reproductive success that currently is preventing species recovery.