A recent study has provided some evidence supporting the hypothesis that light and noise pollution alters the biological clocks of birds living in cities (compared to birds living in rural areas).
Dr. Dominoni (Max Planck Institute for Ornithology, Germany) and colleagues used radio-pulse transmitters attached to European blackbirds (Turdus merula) living in Munich, Germany (city) and those living in a forest nearby to track the animal's activity levels. They found that blackbirds living in the city showed significantly increased activity an average of 29 minutes earlier in the morning than blackbirds living in the forest.
When the birds were housed in a room with constant dim light, effectively eliminating time-of-day cues, the circadian rhythm of the city birds was 50 minutes shorter and the animal's behavioural pattern became irregular more quickly compared to forest birds. The authors speculate that the irregular pattern may help the city birds adapt to their ever-changing, and often unpredictable, environment.
Dominoni DM, Helm B, Lehmann M, Dowse HB, Partecke J. Clocks for the city: circadian differences between forest and city songbirds. Proceedings of the Royal Society B. 280(1763) [Epub ahead of print]