Chip and Dale are not so innocent after all. American ground squirrels appear not only to forage for nuts and seeds, but also to actively hunt for live prey. In the Journal of Ecology write American biologists how in the summer of 2024 they saw dozens of times how a ‘predatory ground squirrel’ chased, killed and devoured a California vole.
Acorns, seeds, nuts, the occasional egg or insect – that was, in biologists’ eyes, the traditional diet of squirrels and ground squirrels. This picture changed in the mid-1990s, when remains of other mammals, amphibians, birds and fish were found in the stomachs of various squirrel species. But whether that was bait or self-caught prey remained unclear.
In any case, it now appears that the Californian ground squirrel does indeed exhibit carnivorous tendencies. The current observations took place in the twelfth year of a long-term study monitoring the behavior of ground squirrels in the wild. In previous summers, nothing unusual was noticed about the squirrels’ feeding behavior. But in July 2024, that changed. There was an exceptionally high ‘vole peak’ that summer – just like with lemmings, for example, numbers can vary greatly from year to year, and high numbers then lead to an increase in predation. It is estimated that in 2024 there were seven times as many voles as in other summers. But where normally the usual suspects While hawks, owls, weasels and herons took advantage of the higher mouse density, another enemy now emerged: the ground squirrel.
Arguing about prey
Normally, California ground squirrels eat seeds and grasses, which are abundant in the study area. Food competition is therefore rare. Yet in this case, the biologists repeatedly observed ground squirrels bickering with each other over vole prey: probably because a single vole is much more energy-rich than all those grasses and seeds, the researchers said. Sometimes they saw more squirrels nibbling on one prey without any jostling – in that case there may have been family connections.
In several cases, the researchers saw how a ground squirrel quietly and low to the ground stalked a vole before striking. Sometimes the squirrel would run after the vole. Captured prey was killed by one or more bites, usually to the neck. The ground squirrel then bit off the vole’s head and then either first stripped the victim’s fur or immediately pulled the meat from the body.
It is striking that both young and old ground squirrels (both male and female) appear to be adept at vole hunting. While hunting is not without dangers, the biologists emphasize: captured voles sometimes bite back viciously. The researchers saw a few times that the ground squirrel released the prey as a result.
Biting a boy to death
It is unknown whether the hunting behavior of ground squirrels is instinctive or learned. The authors suspect the former because the behavior is so widespread (they saw it no fewer than 74 times in two weeks). In passing, they mention that California ground squirrels sometimes also engage in another instinctive and deadly behavior: infanticide. Previous research shows that female squirrels sometimes bite the young of a conspecific to death, probably to reduce competition for their own offspring.
Another question is whether (and if so, how) vole predation will affect the ecology in the area. Ground squirrel population sizes may increase thanks to this energy-rich additional food source – even if the hunting behavior is only temporary and only occurs during years of vole abundance. Such an increase could also benefit animals that eat ground squirrels, such as rattlesnakes, foxes, badgers and raccoons.
On the other hand, it may also be the case that the ground squirrel population is declining because voles carry fleas that can cause bubonic plague in the squirrels.