Crows that Eat McDonalds Cheeseburgers have Higher Cholesterol Levels

Researchers recently studied whether eating highly processed junk food had an effect on wildlife.  Specifically, the researchers tested whether eating McDonald’s cheeseburgers had any effects on crows. The short answer is: Yes. Crows who had McDonald’s cheeseburgers left near their nests had an increase in their blood cholesterol levels.

Study overview

Some wildlife living near humans have learned to become scavengers and routinely eat scraps of fast food and other highly processed foods that humans discard.  Researchers wanted to test whether crows–who are among the wildlife that frequently scavenge human junk food left about in urban areas–are affected by this diet.

The researchers sampled the blood cholesterol levels of 140 crow nestlings along an urban-to-rural gradient in California, returning to track their survival rates after they fledged. 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 also provided nestlings in a rural New York population 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 crows who were fed cheeseburgers ended up with higher cholesterol levels than their neighbors, similar to those of the urban crows in California.

Is higher cholesterol levels in crows a good thing or bad thing?

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

–  Andrea Townsend, researcher, Hamilton College

Should people feed highly processed junk food to crows then?

The researchers do not 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.”


Journal Reference:  Andrea K Townsend, Hannah A Staab, Christopher M Barker. Urbanization and elevated cholesterol in American Crows. The Condor, 2019; DOI: 10.1093/condor/duz040