市郊生活的鸟类比农村鸟类更易“愤怒”

No need to head to the movie theater or download the video game app: Angry Birds can be found right in your backyard this summer--if you live in the suburbs, that is. Virginia Tech researchers recently found that birds that live in suburban areas exhibit significantly higher levels of territorial aggression than their country counterparts. The results were recently published in Biology Letters.

"A possible reason for this is that these birds have less space but better resources to defend," said Scott Davies, a postdoctoral associate in biological sciences in the College of Science. "Living near humans provides better food and shelter, but it also means more competition for these limited resources."

Davies and co-author Kendra Sewall, an assistant professor of biological sciences in the College of Science, measured territorial aggression in 35 urban and 38 rural male song sparrows at three rural and three urban sites in the New River Valley during the spring of 2015. 

The Virginia Tech and Radford University campuses served as the (sub)urban sites due to their levels of human impact. Rural sites included Kentland Farm and Heritage Park. In these settings, the researchers played a recording of a male song sparrow and observed how the territory-holding birds responded to a simulated intrusion from a neighbor.

Campus birds showed a higher level of aggression: they approached and remained near the speaker, flapped their wings furiously, engaged in loud singing and then began to produce 'soft song'--a term that researchers use to describe the quiet, garbled noise that a bird makes, which is predictive of an impending attack.

Though rural birds still responded to a song intrusion, they did not respond as vigorously.

The researchers placed small leg bands on the birds to identify individuals, and recorded each individual's responses twice, several weeks apart. The suburban birds were more territorial on both occasions, showing that their increased aggression persists throughout a breeding season.