House Sparrows (Passer domesticus) have adapted to urban environments, which are changing and growing faster than ever. A range of both biotic and abiotic factors — including habitat fragmentation, changing food availability, heavy metals, nighttime light, noise and urban density — are changing the way birds live in urban environments. By understanding how cities affect birds, scientists can understand and predict how bird populations may change in the future and birds and humans can coexist.
For urban ecologists like Jenny Ouyang, they are the perfect study animal: a way to gain insight into how birds may or may not adapt to the human environment.
“House sparrows are really an ideal way to study urban ecology,” Ouyang said. “They’re human commensals, so they exist everywhere, they’re easily observable, and they’re charismatic.”
In a new study published in the journal of the Ecological Society of America Ecological applications, Ouyang and her team used sophisticated methods to assess the impact of nighttime light, noise and urban density on the health and physical condition of house sparrows. They also examined the birds’ lead and glucocorticoid concentrations and compared them to the birds’ reproductive success. Through their efforts, they discovered that urban density, more than light pollution or noise levels, affects sparrows. The sparrows also carried a much higher charge of lead in their bodies than the researchers had expected.
Most urban ecology studies have used satellite imagery to estimate the urban environment and human population density and have considered the rural-urban divide as a dichotomy. Ouyang’s study is one of a growing number that studies urban environments along a continuum and on a fine scale: in this case, in pieces of two square meters each.
“We’re looking at the environment in small plots, at the scale that the bird would inhabit,” Ouyang said. ‘A sparrow doesn’t care about the whole city. It really inhabits one area, and listens to the noise from that area, and it cares about the number of people from that area. The urban density factor takes into account that cities can be small but dense, and vertical structures are just as important to consider as horizontal ones.”
Ouyang was shocked at how closely the birds’ health correlated with urban density, rather than any of the other components they studied. She was also shocked by the high levels of lead in the blood of the birds they studied and intrigued by the puzzle of where the lead came from.
“They could eat small pieces of gravel like birds have been eating pebbles for millennia to digest their food,” Ouyang said. “Or the lead could be in the water or in the insects via bioaccumulation.”
She and her lab will continue to explore the link between urban environments and bird health, to understand the effects of cities on birds and how urban expansion is changing ecosystems, individuals, populations and genetics.
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Subject of research
Elevated lead and glucocorticoid concentrations reduce reproductive success in house sparrows along an urban gradient
Article publication date
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