California Least Tern Monitoring and Management in San Diego County

Project background

Although nearly 40 years of California least tern monitoring data existed, in 2013 IEMM saw that a comprehensive analysis of this data had never been done.

The California least tern (Sternula antillarum browni) was listed as endangered in 1970. Since then, the species population has been monitored annually.

The number of breeding pairs had gone from just 624 in 1973 to about 6500 in 2010. While the number of breeding pairs had increased substantially, fledgling success remained extremely low and appeared to be declining.

In order to better understand this anomaly, a more comprehensive understanding of the ecological relationships shaping California least tern population dynamics was needed. 

Filling a research gap

The California least tern recovery plan identifies specific goals and many management strategies have been successfully implemented to meet those goals. Yet, monitoring and management of the species had been largely site-specific and decentralized.

Led by IEMM in 2014, this project is facilitating the implementation of a scientifically robust, statewide monitoring and management program for California least terns. Species recovery objectives and current understanding of California least tern ecology guided IEMM’s research goals.

Project Goals

Adopting a robust meta-analytical approach, two goals were established for this project:
1. Identify population trends, and the drivers of those trends
2. Evaluate current monitoring and managing practices

IEMM began by reviewing the current monitoring and management strategies. The utility and efficacy of monitoring and management protocols to track tern population status are being evaluated.

Findings and recommendations

The research analyses thus far has identified knowledge and methodology gaps that can guide future research needs and strengthen the California least tern recovery plan.

The findings illuminate areas of research where there are gaps in type and consistency of data collection. For example, there were scarce data for rates of predation and fledgling mortality. Filling gaps such as these could be beneficial and critical for recovery of the species. 

Also, IEMM has provided recommendations for improving the effectiveness and efficiency of California least tern conservation efforts. These efforts, along with IEMM’s ongoing research on this project, can help long-term efforts to mitigate threats and stressors facing tern populations.

See our project report to learn more:

Long-term Analysis of California Least Tern Data