What Makes Robins Sing at Night Answers
TEXT 1
Robins in urban areas are singing at night because it is too noisy during the day, researchers suggest. Scientists from the University of Sheffield say there is a link between an area's daytime noise levels and the number of birds active at night. Until now, light pollution had been blamed because it was thought that street lights tricked the birds into thinking it was still daytime. The findings are published in the Royal Society journal Biology Letters.
"You generally only seem to hear nocturnal singing in cities," explained Richard Fuller, one of the study's co-authors. "So this led us to think that there was some aspect of the urban environment that was driving this phenomenon."
Shedding light
Light pollution had been widely held as the prime suspect. It was thought to prevent the birds from roosting, leading to them remaining active through the hours of darkness.
"That was the stock answer you would get," Dr Fuller said, "that it was basically tricking the birds into thinking it was daylight and tripping some sort of physiological threshold. "But we thought that was pretty unlikely because birds are much more complex than that."
He said that there had never been a scientific study to measure the impact of light pollution on the behaviour of urban robins. So we went out and measured both nocturnal light and daytime noise levels and we found that daytime noise had a far stronger effect. We found that night-time light had a small effect, but very much smaller than the impact of noise levels."
This led the team to conclude that it was an active decision by the birds to sing at night rather than passively responding to light levels.
"The birds appear to be singing at night to avoid competition with high noise levels caused by our cities during the day," Dr Fuller suggested. "Noise levels were 10 times higher in places where birds were singing at night."
The findings form a part of a seven-year research programme by the university's Department of Animal and Plant Sciences to measure the impact of urbanisation on biodiversity.
TEXT 2
Urban robins living in noisy areas sing at night because they are more likely to be heard, according to research published yesterday. Scientists in the north of England have discovered that the birds have adapted their behaviour to cope with the pressing demands of modern city life. The study, which appears in the journal Biology Letters, disproves the myth that some robins sing at night because they believe street lighting is daylight. One of those who undertook the research, Richard Fuller of Sheffield University, said: "This shows that there are subtle effects of urbanisation, and that birds are adapting their behaviour to overcome some of these problems."
The researchers recorded sound levels at 121 sites around Sheffield for several months in 2005 and 2006. They found robins singing during the day at 67 sites, and nocturnally at 18. At one site, where daytime traffic created a noise of 69 decibels, the scientists discovered a single robin that sang only at night. Light levels at the different sites were measured by the scientists but was shown to have less of an effect on the robins’ behaviour than noise. The robins' songs, which they use to define and defend their territory as well as attract mates, are slightly higher pitched than traffic sound but the researchers added that increased urban noise levels still manage to drown out the birds' vocal efforts.
This behaviour is not without drawbacks for the bird, one of the earliest to join the dawn chorus. The birds are more likely to tire themselves out with nocturnal singing. Dr Fuller added: "If they are singing at night, it is going to take more energy than sleeping, so this may not be good news for them."
