Changing Diets, Changing Skulls: The Impact of Human Feeding on U.K.’s Red Squirrels

The red squirrel, Sciurus vulgaris, native to the United Kingdom, faces a peculiar challenge due to human intervention. Although cherished by its fan base across Great Britain, many U.K. residents have never seen one. Conservation efforts, particularly from the 1990s to the late 2010s, may have inadvertently altered this beloved species' physical characteristics. In Formby, red squirrels received up to 50% of their food as peanuts from conservationists and tourists. This shift in diet resulted in noticeable changes in their skulls and jaws compared to their counterparts in Scotland.

During this period, scientists observed that Formby's red squirrels developed flatter skulls and jaw muscle attachments closer to the joint, hinting at a less efficient bite. This was a stark contrast to red squirrels thriving on a natural diet of pine nuts, hazelnuts, chestnuts, acorns, and yew, which endowed them with stronger jaws. The University of Edinburgh conducted a study analyzing 113 skulls and 387 jaws donated by conservationists, aiming to measure the impact of diet on bite force.

"We know that bone can and does respond to its mechanical environment."
Source: Phil Cox, an anatomist at University College London

The findings revealed that excessive consumption of peanuts can weaken a red squirrel's jaws. Furthermore, the study highlighted how human feeding practices could lead to significant changes in the anatomy of the animals involved. Remarkably, red squirrels that transitioned back to a natural diet after the late 2010s began to show skull shapes resembling those of their northern relatives, suggesting some level of reversal is possible.

"If you were feeding them food of such sort of mechanical properties that they really did lose the ability to bite very hard at all."
Source: Phil Cox, an anatomist at University College London

Wildlife managers are urged to consider not just the nutritional value but also the toughness of food provided to animals. The transition back to a natural diet underscores the resilience of these creatures, although regaining full bite strength might be a prolonged process.

"They are the native squirrel for the U.K., and yet a large proportion of the population probably has never seen one."
Source: Phil Cox, an anatomist at University College London