Riparian Avifauna of the San Francisco Bay Region: Population Dynamics and Future Outlooks with Anthropogenic Climate Change

Anthropogenic climate change is predicted to drive widespread avian population declines, range contractions, and global extinctions in the coming century. Recent research has largely focused on identifying past trends and phenological disruptions; however, relatively little is known about how climate variation impacts the ultimate drivers of population change: demographic rates.
Throughout my project, I worked to expand this area of research by establishing two new bird banding stations for monitoring demographics and conducting analyses of existing banding data from the Coyote Creek Field Station in Milpitas, CA. I built demographic models in a Bayesian framework to evaluate the effects of growing-season precipitation, spring mean temperature, and mean winter minimum temperature on the adult apparent survival and reproductive success for nine songbird species from 1995–2018. One study species – the San Francisco common yellowthroat (Geothlypis trichas sinuosa) – is of immediate conservation concern. I simulated possible population trajectories for the period 2020–2100 using my estimated parameters and the predicted local climate from two global climate/circulation models under three future greenhouse gas emissions scenarios.
The demographic rates for six of these species were significantly affected by local climate variation. Reproduction was highest in years with the most growing-season precipitation and warmest spring mean temperatures. In contrast, adult apparent survival was lowest in years with the highest growing-season precipitation. There were several interesting exceptions to these general patterns as well. Among the study species, climate variation most impacted the survival and reproduction of the San Francisco common yellowthroat. Simulations with projected climate change suggest that this population will decline over the next 80 years.
To my knowledge, this is the first study to simulate population trajectories for a North American songbird species under future climate scenarios. The models show that immigration may buffer climate effects, which suggests metapopulation management of this species will be beneficial. This study highlights how population demographics can be applied to conservation and demonstrates the need for expanded research in this area.