Pollution can actually lead male birds to change their tune, singing better than before. This could lead to birds that prefer pollution, to their ultimate detriment.
Scientists focused on wild European starlings (Sturnus vulgaris) that were foraging for earthworms at a number of sewage treatment plants. These areas were contaminated with pollutants that mimicked estrogen.
After determining what pollutants the birds were exposed to, behavioral ecologist Shai Markman at Cardiff University in Wales and his colleagues fed starlings mealworms that either were clean or were dosed with the same pollutants.
The researchers found the pollutants markedly enlarged the area of the brain that controls song complexity in the male birds. The males sang more often and developed longer and more complex songs that females preferred.
"This is the first evidence that environmental pollutants not only affect, but paradoxically enhance a signal of male quality such as song," said researcher Katherine Buchanan, a behavioral ecologist at Cardiff University.
Unfortunately, the pollutants also debilitated the birds, hampering their immune systems. The concern now is that females will prefer males that sing well but are in poor shape.
"Our results suggest female birds should prefer to mate with males that forage on polluted prey," Buchanan said. "That's bad because we know the pollution affects immune function. We don't know whether it also affects their ability to find food for offspring, or their fertility. The pollution could have dramatic effects on their population."
"It's extremely likely that a whole range of birds will be affected the same way," Buchanan added. "We know corvids — magpies and crows, for instance — use these sewage treatment plants as foraging places when food is in short supply."
The effects of these pollutants on females remain uncertain. "We could see hypermasculinazation of these females, with females starting to sing when normally they don't," Buchanan said.
Markman, Buchanan and their colleagues detailed their findings Feb. 27 in the journal PLoS ONE.