Crows eating cheeseburgers have higher cholesterol levels – just like us | NOVA | PBS | NOVA

Aside from the problem of birds against mammals, crows and humans have a lot in common. Like us, these intelligent corvids have great memories and a penchant for riddles. They can create and use tools and move around the world in complex social groups. They are even a bit monogamous, just like us.

Now, the less glowing news: crows are also greedy for junk food – and their bodies are not immune to its effects. In a study published today in the journal The Condor: ornithological applications, Scientists have found that crows in cities tend to have higher cholesterol than their rural cousins. The culprits, it seems, are the diets similar to those of the man they adopt, including McDonald's fat and calorie-dense cheeseburgers that line many urban streets.

This fat peak is not necessarily alarming, however, and it is not yet proven that high cholesterol has a long-term impact on the health of the crow. But the case of crows has always been complex because these birds are among the few species that prosper in an urban environment.

In the United States, the American crow (Corvus brachyrhynchos) Effectively controls a range from one ocean to another, partly because of its brave combination of mental acuity and an apparent steel stomach. While crows in the countryside often eat fruits, nuts, insects and small mammals, these opportunistic omnivores will swallow just about anything they need, including garbage all the way up.

In many cases, this indiscriminate meal is very useful: food is food, whether it is served on a silver tray or pulled from the mud at the bottom of a dumpster. But the modern human diet, especially in Western countries, contains many highly processed, high-calorie products, and the contents of garbage are often quite different from what these birds (or any other animal) have evolved to feed themselves. .

Researchers have known for years that people in urban areas tend to have higher cholesterol levels than those in rural areas. For example, the author of the study, Andrea Townsend, a behavioral biologist at Hamilton College, was not terribly surprised when the analysis of 140 chicks of American crows from Davis, California, showed the same trend.

To link the discovery more directly to the diet, the researchers then designed a Super size me configuration with a new cohort of crows in upstate New York. During the nesting seasons of 2017 and 2018, Townsend and her colleagues spent their days throwing cheeseburgers in front of known crows' nests – baits that inevitably aroused the interest of the parent birds, who brought the sweet treats to their little ones .

The experiment required a steady supply of fast food and the team became a regular at the McDonalds restaurant in Clinton village, where they often ordered one hundred burgers at a time. "The employees were very shocked and horrified," says Townsend. (The crows, on the other hand, "seemed delighted with the design of the study," she says.)

After several weeks of cheeseburger diet, chicks had more cholesterol in their blood than baby birds that had not received any more food. The crows stay in the nest until they are about a month old, after which they become much more difficult to catch, Townsend explains. For this reason, it is unclear whether these birds in particular have maintained high cholesterol levels or have suffered long-term adverse effects.

The fast food solution can have even help Birds: Before the cheese chicks did not fly in the cage, they were bigger and heavier. According to Townsend, it is good that living in the crows community is a good thing. Young corpulent birds tend to be healthier in adulthood.

This result seems to be reinforced by another of the chicks that the team had studied in California. During the two or three years following the flight of these crows, the researchers monitored them to determine whether high cholesterol levels in the young had an impact on survival. In contrast to Townsend's expectations, this was not the case: Basically, crows from across the spectrum of cholesterol seemed to have the same results.

The reasons for this are not entirely clear. But while there is a clear threshold for "desirable" cholesterol levels in humans, there are no such statistics for our feathered friends – and higher cholesterol in young people does not necessarily mean having high cholesterol in adulthood.

In other words, crows can simply use the molecule wisely. Despite its bad reputation in the world of nutrition, cholesterol is essential to animal life and is an important structural element of cells. It's important enough that our livers feed on a regular basis – and an unusually low cholesterol level in humans can cause health problems.

Thus, with respect to bird health and cholesterol, "there is no simple answer at this stage," says Anne Clark, ecologist and raven expert at Binghamton University, who did not participate in the event. 'study. But, she adds, it may be expected. "Relationships between humans, food and urban animals will inevitably be complicated, in the same way that it's complicated to have a good diet at the modern age."

Nevertheless, the absence of negative effects on these birds should not be considered as an invitation to exercise caution (or cheeseburgers) in the wind, says Townsend. The study followed his subjects with feathers only for a few years – but crows can live more than 15 years in the wild and over 50 years in captivity. If cheeseburger intervention or follow-up had been longer, things may have been different, she says.

These results will not necessarily be the same for other species. Sparrows, foxes, iguanas and turtles also seem to benefit from an urban cholesterol regain, but the ultimate consequences of these changes remain unclear for the most part. Because of their dietary flexibility, crows may be one of the most suitable creatures to avoid occasional hamburgers, says Corina Newsome, wildlife biologist and conservation ecologist at Georgia Southern University, who did not participate in the event. the study. But this will not be the case for all animals, or even for all birds, she says.

Things get even more complex when you consider the impact of urbanization on animal welfare, says J. Drew Lanham, wildlife conservation specialist and Clemson ornithologist. University, who did not participate in the study. The Townsend team did not find a link between cholesterol and crows, but a disturbing trend emerged: the more urban a bird's habitat is, the lower the probability of survival. .

"Something is happening in an urban setting, whether it's psychological or physiological, that impacts well-being," says Lanham. "It makes me think of things like stress … and what an urban environment imposes on the body and the mind."

According to Newsome, these prolonged uncertainties may be one more reason to keep wildlife, especially in terms of nutrition. After all, "if it's not healthy for us, it's probably not healthy for them."