Crows shouldn’t have fries with that

Scavenging for scraps is a smart survival tactic for city birds, but there may be a downside. Though that’s not clear.

A new study suggests that a diet of human foods such as discarded cheeseburgers is giving crows living in urban areas in the US higher blood cholesterol levels than their rural cousins.

A team led by Andrea Townsend from Hamilton College in New York sampled the blood cholesterol levels of 140 crow nestlings along an urban-to-rural gradient in California, returning to track their survival rates once they were ready to fly. {%recommended 7482%}

They found that the more urban the environment, the higher the blood cholesterol of the crow nestlings raised there. 

To test this further, they provided 86 nestlings in rural New York with a regular supply of McDonald’s cheeseburgers and compared their blood cholesterol levels with those of nearby crows who had to fend for themselves. 

The burger eaters recorded higher cholesterol levels – similar to those of the urban crows in California.

But while survival rates were lower for urban crows than rural ones during the first three years of life, cholesterol wasn’t the culprit. In the New York population, nestlings with higher cholesterol actually scored higher on measurements of their body condition. 

“Despite all the bad press that it gets, cholesterol has benefits and serves a lot of essential functions,” says Townsend. 

“It’s an important part of our cell membranes and a component of some crucial hormones. We know that excessive cholesterol causes disease in humans, but we don’t know what level would be excessive in a wild bird.”

Still, Townsend doesn’t recommend putting burgers in bird 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. 

The findings are published in the journal The Condor: Ornithological Applications

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