Urban Heat Island Effects on Songbirds Physiological and Behavioral Stress Responses

Background/Question/Methods

There has been an alarming decline in bird populations, correlated with rapid temperature increases due to climate change, in addition to other global changes. Birds have had to either adapt to, exploit, or avoid urbanizing areas. In urban environments, impervious surfaces further elevate temperatures, forming areas within cities that are substantially warmer than their surroundings, in what is known as the urban heat island effect. Overall, urban heat islands have contributed to changes in bird behavior, physiology, and reproductive success. We explored the question, how do Urban Heat Islands (UHIs) affect songbird physiology (metabolic rate) and behavior (activity level)? We hypothesized that UHIs (measured by % impervious surfaces and interpolated weather station data) would result in higher physiological stress for songbird nestlings. We also hypothesized that UHIs would inhibit songbird activity. We explored the physiological aspect of this question by using pull flow-through respirometry methods to calculate the average resting metabolic rate of House Wren nestlings along an urban to rural gradient. In addition, we observed songbird behavior in more or less impervious surfaces to examine impacts of UHI on activity level.

Results/Conclusions

This project studied behavior and physiology in the field to investigate the effects of increasing temperatures exacerbated by the urban heat island effect on songbirds. Included in the study were 33 focal sites, ranging in temperature and impervious surface. Temperatures included in the study ranged from 59.70 to 85.50 degrees. Impervious surfaces included in the study ranged from 0% to 48.47%. To determine a significant relationship between total activity levels and daily average temperature, I ran a linear regression to determine if this relationship is statistically significant. Since this relationship meets the statistically significant p-value assumption, then it is accepted that this relationship is statistically significant. In contrast, I can not accept a statistically significant relationship between % impervious surfaces and total activity level since the linear regression model does not output a p-value that meets statistical significance. Although there is a slight correlation, determining statistical significance would require more data. In conclusion, as temperature increases across sites total activity level of songbirds also increased. A better understanding of the relationship between UHI (% impervious surface and temperature) and songbird stress responses (physiological and behavior) can help to predict climate change impacts on songbirds. This research will increase our understanding of how birds will respond to the impacts of climate change, informing strategies for bird conservation. The methodologies used here can serve as a model to study the effect of global change on other urban species. As the expansion of urban areas increases, understanding birds’ behavioral and physiological stress responses will provide insight into the broader phenomenon of climate change on bird populations.