Patterns of Passerine Abundance and Effects of Precipitation at a Banding Station in the California Bay Area

Background/Question/Methods

In California we have had a long history with droughts, and as the planet continues to be affected by climate change we expect this trend to continue. The goal of this study was to see if the abundance of eighteen different bird species were affected by lack of precipitation. We chose resident, wintering and migratory birds to see if there would be a noticeable difference between their population numbers. To do this, we took historical bird banding capture data and assisted in the collection of the most recent data from the Coyote Creek Field Station in Milpitas, CA. Weather data from the nearby Moffett Federal Airfield Weather Station was analyzed to find the total monthly precipitation and compared to the total number of birds caught monthly starting in the year 1998. Our data analysis showed distinct migration and breeding patterns for each species chosen. A major part of our project was our use of a programming language called R to make ggplots, collect p-values and assess significance, and produce Generalized Additive Models, or GAMs for short. When analyzing data we looked at two lag periods, one month and one year, to assess the delayed effect of precipitation.

Results/Conclusions

We found that migratory species are more likely to show a significant negative correlation with rainfall than resident birds. It was much more likely for a species in decline to have their numbers affected by rainfall either through positive or negative correlation. However our results were not conclusive enough to say that precipitation alone affects the quantity of birds that will be seen one month and one year later. Our research presents the potential importance of precipitation to the survival of birds under climate change.