Spotted Owl Metapopulation Dynamics in Southern California

H. RESIT AKCAKAYA
Applied Biomathematics, 100 North Country Road, Setauket, NY 11733, USA

Summary

1. The California spotted owl Strix occidentalis occidentalis (Xantus) is found in the Sierra Nevada and in a series of isolated populations in the mountains of southern California.
   
2. We developed a model to assess the risk of decline of the southern California spotted owl metapopulation. We modelled the spatial structure of this metapopulation by incorporating distance-dependent dispersal and correlation among the population growth rates.
   
3. Demographic characteristics of the largest insular population were estimated from colour-ringing the majority of the territorial population. This owl population declined dramatically during the study period, 1987-1993.
   
4. If the observed decline continues and similar declines are occurring in the other populations, our viability analysis predicts that this metapopulation has a high risk of going extinct in the next 30 to 40 years.
   
5. If the observed decline is due to naturally occurring environmental fluctuations (drought), and thus temporary, the model results indicate substantial decline, but a low probability of total metapopulation extinction.
   
6. Our results indicated that the risk of decline is quite sensitive to the correlations among population growth rates. Increased correlation increased the risk of decline.