October 3, 2017
Despite being well-adapted to urban life, house sparrow numbers are falling. A study in open-access journal Frontiers in Ecology and Evolution finds that compared to sparrows living in the country, urban-dwelling birds show clear signs of stress linked to the toxic effects of air pollution and an unhealthy diet. This could have health implications for people living in cities.
"We find that house sparrows living in the city are suffering from more stress than those living in the countryside, and we link this to differences in air quality and diet," says Amparo Herrera-Dueñas, who completed this work in collaboration with the Department of Zoology and Physical Anthropology at the Complutense University of Madrid, Spain.
"It is particularly bad for urban birds during the breeding seasonwhen they are torn between allocating resources towards fighting the toxic effects of pollution or towards laying healthy eggs, both of which aren't helped by their poor diet."
She adds, "If our cities are unhealthy for birds, which is what our study is suggesting, then as their neighbors we should be concerned because we are exposed to the same environmental stressors as house sparrows."
Stress measured in urban, suburban and rural sparrows
Herrera-Dueñas and her colleagues used a non-invasive method to sample the blood of hundreds of sparrows from rural, suburban and urban areas around the Iberian Peninsula in Spain.
"We took a small blood sample from each bird, according to its weight and physical condition, and released them unharmed," she explains. The samples were analyzed for signs of oxidative stress, which can be used to measure how much an environmental stressor, such as pollution, is weakening the bird's natural defenses.