It’s no secret that human-provided food can impact wildlife. But as wildlife is increasingly found in urban areas, it can be hard to stop animals like birds from snacking on our food. One consequence, researchers found, is that city living is driving up the cholesterol levels of crows.
“Urban crows had higher cholesterol than rural crows,” said Andrea Townsend, an assistant professor of biology at Hamilton College and the lead author of a study published recently in The Condor: Ornithological Applications.
Take the example of the bird nicknamed Canuck the Crow, who became famous for raiding a McDonald’s in Vancouver among other incidents. Townsend had also seen other research showing species like green sea turtles (Chelonia mydas), rock iguanas (Cyclura spp.) and San Joaquin kit foxes (Vulpes macrotis) found around humans had high cholesterol levels. She and her co-authors wanted to see if American crows (Corvus brachyrhynchos) near cities were also affected by human food.
“Human food in general is very different from [crows’] natural food sources. It’s much higher in calories, higher in fat. It’s processed,” she said.
The researchers first took blood samples from more than 100 crow nestlings around Davis, California, in areas ranging from urban to rural. They found that chicks in more urban areas had higher cholesterol than those in rural areas.
To find out if human food was responsible, they ran a second test in which they fed nestlings McDonald’s cheeseburgers and compared their cholesterol levels after several weeks with other nestlings that ate a natural diet.
“The cheeseburger crows had higher cholesterol levels than the regular crows,” Townsend said.
In fact, the ones that ate McDonald’s seemed a little heavier, which is generally a good thing for growing nestlings.
“Chubby birds are generally considered to be in good condition,” she said.
However, she cautions, these results shouldn’t be taken to mean that people should go out and feed cheeseburgers to crows. Heavier birds may have more difficulty escaping from predators, and there might have been other costs to eating cheeseburgers that were not measured in this study.
As part of the first test, the researchers also followed birds with high cholesterol and those without for three years, but they didn’t find the cholesterol caused higher mortality. But Townsend said that even in humans, health problems associated with high cholesterol usually manifest later in life. Since crows live about 15 years, she suspects three years wasn’t enough to show these kinds of effects.
She notes that cholesterol isn’t always bad — humans need some level of cholesterol for cell functions, steroid development and other things. It’s only when it becomes excessive that it becomes a problem.
The trouble is, we don’t know what constitutes high cholesterol in wildlife, or when it might become a problem for endangered wildlife with a diet of human food.
|Joshua Rapp Learn is a science writer at The Wildlife Society. Contact him at firstname.lastname@example.org with any questions or comments about his article.
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