Life In The Big City: Urban Crows Developing High Cholesterol From Discarded Human Food

CLINTON, N.Y. —¬†When one stops to consider life in a big city, the local wildlife isn’t typically one of the first topics that come to mind. Sure, most cities are home to millions of birds, cats, rodents, and others, but for most residents these animals tend to blend into the background and go unnoticed. All of these urban-living animals have to find their food somewhere, and most end up eating up the leftover scraps and food bits tossed out by humans — which begs the question: how is a diet of almost entirely human food affecting these animals and their health?

A new study conducted by researchers at Hamilton College set out to answer that question, and found that urban crows are displaying much higher blood cholesterol levels than their rural counterparts. Researchers theorize this discrepancy is due to urban crows regularly eating discarded, processed human food, such as fast-food cheeseburgers.

A total of 140 crow nestlings (babies) were sampled for blood cholesterol levels by researchers. All of the nestlings were located along an urban-to-rural road in California, and each crow was tracked and followed up on in order to keep tabs on their survival rates.

Across the board, researchers found that crows living in urban environments displayed higher cholesterol readings.

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So, now that they had established that urban crows did indeed exhibit higher cholesterol levels, researchers wanted to test if human food was the culprit. In order to do this, they provided a group of nestlings in rural New York state with a steady diet of McDonald’s cheeseburgers, and then compared the fast-food-eating crows’ cholesterol levels with another group of nestlings who had found their own food. As expected, the cheeseburger-eating group of crows had higher cholesterol levels than the control group.

Despite the general belief, especially regarding humans, that high cholesterol levels are unhealthy, researchers say they actually aren’t so sure that’s the case when it comes to crows. Surprisingly, among the New York population of studied crows, those with high cholesterol scored higher¬†than other crows in measurements of overall body health and condition.

That being said, survival rates among studied urban crows over the first three years of their life were still lower compared to rural crows, but researchers say they do not believe higher cholesterol levels were to blame.

“Despite all the bad press that it gets, cholesterol has benefits and serves a lot of essential functions,” explains lead author Andrea Townsend in a statement. “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.”

At the end of the day, though, the study’s authors say it’s still probably not a good idea to share your next fast-food meal with a nearby bird.

“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,” Townsend says. “Feeding wild birds can be a great way to connect with nature, and it can be a refreshing change to think that we’re doing something that helps animals out. 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.”

The study is published in The Condor: Ornithological Applications.

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