City living is producing something new for you to worry about: high crow-lesterol (sorry, I’m sorry, I’m trying to delete it).
Crows generally aren’t picky eaters, and primarily survive on plants, carrion, and food scavenged from human-produced sources like landfills and garbage cans. But the food we throw away might not be as healthy for these scavengers as the food they’d find in a people-free environment. Scientists wondered whether crow diets were suffering from urban living. So, naturally, they fed the corvids some McDonald’s cheeseburgers and then analyzed their blood.
Cholesterol is an important molecule for bodily function, but too much has been linked to disease in humans. What too much cholesterol does to other animals, scientists aren’t sure of. A team led by assistant professor Andrea K. Townsend at Hamilton College in New York set out to measure the effects of urbanization and a low-quality diet on crows’ cholesterol levels and overall survival.
The researchers banded and took blood samples from 140 crow nestlings in Davis, California, and 86 crow nestlings in the Clinton, New York, and monitored them for either two or three years. For some of the crow families in New York, the researchers supplemented their diet by placing a McDonald’s cheeseburger within 33 feet of their nest, five to six days a week.
Urban environments (which the researchers defined as environments with more impervious surfaces) seemed to be associated with higher cholesterol levels, as well as decreased survival. And the fledgelings of the burger-fed birds seemed to have higher cholesterol, on average, than those that didn’t receive burgers.
But it’s unclear whether cholesterol itself was a good or bad thing for the birds, and the burger-fed birds seemed to be in better condition than the birds who didn’t receive McDonalds. It’s also unclear what constitutes “high cholesterol” for a crow. However, it is clear that urbanization overall seemed to have a negative effect on crow survival for the first three years of life, according to the paper published in The Condor: Ornithological Applications. The results seem to match those of other experiments on house sparrows, Northern Bahamian rock iguanas, and San Joaquin kit foxes, in which urban populations (or populations in area with more humans) are found to have higher cholesterol.
There are still plenty of questions left unanswered by a study like this. The researchers only monitored the young crows for two to three years—what about the effects of a fast-food diet on older crows? The researchers concluded that they’d need to observe crows for longer in order to fully understand any possible ill effects that higher cholesterol might have.
This all goes to show that city living doesn’t just change humans—it changes the animals in our urban habitats, too.