July 13, 2012
House Sparrows Threatened By Urban Noise
Lawrence LeBlond for redOrbit.com - Your Universe Online
Man-made noise is something that will likely never go away, yet, long-term exposure to the commotions of everyday hubbub is increasing the likelihood of many health issues for us humans. But humans aside, the ever-droning din of our everyday cultures are also taking a toll on birds, particularly house sparrows.
In the United Kingdom, the house sparrow population has been in decline since the 1970s, and noise pollution could be linked to the mortality rate being observed in young house sparrows across the country. Researchers believe man-made noise could keep adult birds from hearing the hunger calls of their dependent offspring.
To investigate the issue, researchers from the University of Sheffield followed sparrows on Lundy, a 1,100-acre island located 12 miles off the coast of North Devon, to record how these songbirds are affected by man-made noise pollution.
Julia Schroeder, coauthor of the study appearing in the journal PLoS One, said birds that nest in noisy areas were found to be less effective at feeding their chicks than those nesting in quieter places.
Schroeder noted that the study happened more-or-less by chance. “When I first went to the island, which is very remote and quiet - apart from gulls and shearwaters - I entered a barn and it was very loud.” The barn contained a deafening generator, yet sparrows continued to nest in the building.
Schroeder, wondering if the conditions were affecting songbirds, delved in to find out. “I found that there was a reduced fitness - a reduced reproductive output from the nest boxes located in the noisy area," she told Mark Kinver of BBC News.
In testing the findings about how noise could affect birds, Schroeder explained the main theory “regarding breeding output is that it affects mate choice decisions.” However, the findings did not match up with the existing theory.
“In our case, we saw that the birds did not feed the chicks as well as the birds in the quiet area - this was a novel idea that had not been shown before,” she said. “Obviously, chick provision is strongly linked to chick survival because if they do not get fat then they die.”
Schroeder noted that surviving chicks reared in the noisy environment were also much lighter when they fledged compared to birds in quieter areas, strongly supporting provision behavior, which suggests that noise interrupted the communication between young birds and their parents.
The UK sparrow population has declined by 71 percent since the 1970s -- with some of the sharpest declines seen in urban areas. Schroeder compared the generator in the barn where the study took place with the noises found on any urban street filled with the constant hum of passing traffic.
In the past, studies of this kind focused on mate choice, where the male advertises its quality to the female, said Schroeder. “But the idea that the communication between parents and offspring could be affected in cities is fairly new,” she added.
Another study in 2007, also conducted by researchers at Sheffield and published in the journal Biology Letters, found that robins living in urban settings chose to sing and communicate at night in order to avoid the noise during the daytime.
Until that research was conducted, it was believed that these birds chose to sing at night because they were disturbed by light pollution.
Schroeder´s work is important because it shows that man-made noise could be directly affecting the livelihood of birds.
However, the study sample was small and there could be other factors that are causing these young birds to experience mortality at such a young age, noted Schroeder.
Her study only looked at nest boxes in one noisy site, which may differ from other similarly noisy sites. But because Schroeder found that only chicks were affected, it seemed indicative that the noise pollution played a significant role in their mortality rates, given that the parents could not hear their calls when away from the nest.
“If what we suggest takes place in cities too, it is likely to play an important role in the sparrow population dynamic, and is probably one cause of the dramatic population crash that we are currently observing,” added Schroeder.
Schroeder next wants to work out exactly why the chicks get less food amid the generators´ hubbub. Maybe the parents cannot hear them begging, or maybe the chicks do not beg enough because they can´t hear their parents return (eyesight in chicks is very poor at an early age). Also, perhaps the noise drives off potential insect prey as well, leaving birds to travel farther in search of food.
“It will be interesting to compare stress hormone levels of parent birds and chicks from nest boxes in the noisy area, with those breeding elsewhere,” Schroeder said. “It would be interesting to experiment with noise-insulated nest-boxes.”
Current estimates place about 3.7 million nesting house sparrow pairs in the UK. While numbers continue to decline in England, other areas such as Scotland and Wales have recorded an increase in recent years. Perhaps those places have much less piercing man-made noise levels where birds can flourish.