California Least Tern

Metapopulation Dynamics of the California Least Tern

H. Resit Akçakaya
Applied Biomathematics, 100 North Country Road, Setauket, NY 11733, USA

Jonathan L. Atwood
Antioch New England Graduate School, 40 Avon Street, Keene, NH 03431, USA

David Breininger
Dynamac International, Dyn-2, Kennedy Space Center, FL 32899, USA

Charles T. Collins
Department Of Biological Sciences, California State University, Long Beach, CA 90840, USA

Brean Duncan
Dynamac International, Dyn-2, Kennedy Space Center, FL 32899, USA

Summary

        The California Least Tern (Sterna antillarum browni) is federally listed as an endangered species. Its nesting habitat has been degraded, and many colony sites are vulnerable to predation and human disturbance. In this study, we developed a metapopulation model for the California least tern that can be used to predict persistence of populations along the Pacific coast and the effects of various management actions. We demonstrate the use of the model by estimating the effect of reducing predation impact in various populations. Apart from restricting human access to nesting sites, most management efforts have concentrated on predation, an important source of reduced fecundity. In the model, each cluster of nearby colonies is defined as a population. Within each population, the model includes age-structure, year-to-year changes in survival and fecundity, regional “catastrophes” (strong El Niño/Southern Oscillation events), and local catastrophes (reproductive failure due to predation). The model predicted a continuing population increase and a low risk of a substantial decline in the next 50 years. However, this result was sensitive to assumptions about vital rates. Under a pessimistic scenario, the model predicted a high risk of decline, although a low risk of extinction. We simulated the effect of predator management by reducing the probability of reproductive failure due to predation. The improvement in viability was not the same for management in all populations (it ranged from 1% to 4% for single populations, and up to 8% when all populations were included). Results indicated that the number and location of populations selected for focused management influenced the effectiveness of management efforts.

This study was presented at the 2001 Annual Meeting of the Society for Conservation Biology, and is summarized in:

Akçakaya, H.R., J.L. Atwood, D. Breininger, C.T. Collins, and B. Duncan. 2003. Metapopulation dynamics of the California least tern. Journal of Wildlife Management 67:829-842.