Red Squirrels Fed By Humans Have Experienced Changes To The Shape Of Their Skulls And Lost Muscle Mass

Red Squirrel in the forest
Menno Schaefer - stock.adobe.com - illustrative purposes only

In a town on England’s west coast, red squirrels fed by humans were found to have lost muscle mass and experienced changes to the shapes of their skulls. A team of researchers compared the remains of squirrels in the area before, during, and after human feeding.

Red squirrels are the only species of squirrel native to England. But over time, they have been edged out by non-native gray squirrels, which were introduced to England from North America in the late 1800s. Since then, the number of red squirrels has been declining, and they are now considered a protected species.

Today, there are approximately 287,000 red squirrels left. Their population is mostly restricted to Scotland, northern England, Wales, and some offshore islands.

As the number of red squirrels dropped, people around England started feeding them peanuts. In a town called Formby, both citizens and conservationists began feeding the local red squirrels. From the 1990s to the 2010s, the free peanuts became their main source of food.

Eventually, experts started issuing warnings to residents about how the feeding could lead to negative outcomes, such as starvation during bad weather. So, they switched to harder nuts, like pine and hazelnuts, the type that squirrels would eat naturally.

The research team decided to study the remains of squirrels to learn more about what they were like during the peanut-eating era. Overall, they examined 113 skulls and 387 jaws.

One pattern they detected was that the skulls of the Formby squirrels that had eaten a lot of peanuts were much flatter than those in Scotland. In addition, jaw muscle attachment sites were closer to the joint that helps with chewing.

These differences indicate that the Formby squirrels had smaller, weaker, and less efficient bites compared to red squirrels from other populations.

The changes could be the result of random genetic mutations or inbreeding, as the Formby squirrels have fallen victim to disease before, which decimated their numbers.

Red Squirrel in the forest
Menno Schaefer – stock.adobe.com – illustrative purposes only

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However, the differences in skull and jaw shape suggest that diet could be an underlying cause. Peanuts have softer shells that can easily be broken open.

So, a diet consisting primarily of peanuts may have reduced the squirrels’ ability to eat nuts with harder shells, like hazelnuts.

The less mechanically demanding diet drove changes to the skull and jaw anatomy of red squirrels at Formby. When supplementary peanut feeding was put to a stop, the changes were partially reversed.

The researchers believe their work shows how human feeding can negatively impact wildlife. This may have important implications for the conservation of red squirrels. In the future, it would probably be best to match any supplementary foods to what animals would eat in the wild.

The study was published in Royal Society Open Science.

Emily  Chan is a writer who covers lifestyle and news content. She graduated from Michigan State University with a ... More about Emily Chan

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