Recovering leftovers is a smart survival tactic for the city's birds, but there may be a disadvantage. Although it is not clear.
A new study suggests that a diet consisting of human foods, such as discarded cheeseburgers, gives crows living in urban areas of the United States a higher blood cholesterol level than their cousins Rural areas.
A team led by Andrea Townsend of Hamilton College, New York, analyzed cholesterol levels in the blood of 140 chicks of crows along an urban-rural gradient in California, to look back on their survival rate a year earlier. once they were ready to fly.
They found that the more urban the environment, the higher the cholesterol levels in chicks raised in the crows population.
To test this more, they provided 86 chicks from the New York countryside with a steady supply of McDonald's cheeseburgers and compared their blood cholesterol levels to those of neighboring crows who had to fend for themselves.
Burger consumers have higher cholesterol levels – similar to urban crows in California.
But while survival rates of urban crows were lower than those of rural crows during the first three years of life, cholesterol was not the culprit. In the New York population, chicks with high cholesterol levels actually did better on their fitness measures.
"Despite all the bad press it receives, cholesterol has benefits and performs many important functions," Townsend said.
"This is an important part of our cell membranes and some essential hormones.We know that an excess of cholesterol causes diseases in humans, but we do not know what level would be excessive in a wild bird. "
Nevertheless, Townsend does not recommend putting hamburgers in bird feeders.
"Wild birds have not evolved to eat processed foods and this could have negative consequences that we have not measured or will only manifest over longer periods of time," she says.
The results are published in the journal The Condor: Ornithological applications.