Animals that do well in urban areas tend to be the ones that learn to make use of resources such as the food humans throw away. But is our food actually good for them?
A new study published in the Ornithological Applications journal suggests that a diet of human foods such as discarded cheeseburgers might be giving crows living in urban areas higher blood cholesterol levels than their rural cousins.
During the study, Dr. Andrea Townsend and her colleagues from the Hamilton College sampled the blood cholesterol levels of 140 crow nestlings along an urban-to-rural gradient in California. They found that the more urban the environment, the higher the blood cholesterol of the crow nestlings raised there.
To directly test the effects of human food, the researchers divided rural crows from New York into two groups. One of them was provided with a regular supply of McDonald's cheeseburgers, then, their blood cholesterol levels were compared with the other crows that had to fend for themselves. The crows that were fed cheeseburgers ended up with higher cholesterol levels than their neighbors, similar to those of the urban crows in California.
Then, the researchers estimated the longevity among the different types of crows. Survival rates during the first three years of life were lower for urban crows than rural ones.
Although the cholesterol rate was higher in urban crows, the research team suggested it wasn't the culprit.
"Cholesterol has benefits and serves a lot of essential functions. It's an important part of our cell membranes. We know that excessive cholesterol causes disease in humans, but we don't know what level would be 'excessive' in a wild bird," says Townsend.
Still, Townsend doesn't recommend that people start tossing cheeseburgers or other processed foods to the birds at their feeders. "Wild birds haven't evolved to eat processed food, and it might have negative consequences that we didn't measure, or that will only show up over longer periods of time," she says.
"Feeding wild birds can be a great way to connect with nature. At the same time, though, I do worry that some of the foods that humans give to wild animals, and living in an urban environment in general, might not be good for their health," she explained.
