Humans may inadvertently be contributing to increased blood cholesterol level in crows living in urban areas. Those are the findings of a new study published last week in the journal The Condor.
Researchers found that crows living in urban areas had higher blood cholesterol levels than their rural counterparts because of their varying eating habits.
Hamilton College ornithologist Andrea Townsend and her colleagues measured cholesterol in blood samples from 140 crow nestlings in rural, suburban and urban areas in California over a period of three years.
They also measured the birds’ body mass and fat reserves, and tracked their survival rates, finding blood cholesterol level in the crow nestlings increased as the surroundings got more urban.
The researchers then ran a “cheeseburger supplementation experiment” by leaving McDonald’s cheeseburgers near crow nests in rural New York, New Scientist reported.
The cheeseburger-fed crows had higher cholesterol than nearby rural crows and cholesterol levels more similar to crows living in cities, being about 5 per cent higher than their burger-deficient neighbours.
Townsend said these results are consistent with the handful of other studies on cholesterol in animals living near humans, such as foxes, sparrows and even sea turtles.
“All of these species tend to have higher cholesterol levels in places where they interact with people,” Townsend said.
The researchers found that while urban crows had lower survival rates overall, the cholesterol didn’t seem to hurt the crows, and even boosted the body condition of the nestlings.
“If you’re a chubby crow, essentially, that’s considered to be good condition,” Townsend told National Geographic.
But she still doesn’t recommend feeding burgers to birds. “We know that excessive cholesterol causes disease in humans, but we don’t know what level would be ‘excessive’ in a wild bird,” the New Scientist quoted Townsend as saying.
“It is also possible that, if elevated cholesterol does have negative effects, they would show up later. In humans, it can take many years for excessive cholesterol to lead to disease.”