Interspecific Killing — The Prairie Dog Project

The white-tailed Prairie dog kills

Wyoming Ground Squirrels

In March of 2016, National Geographic featured an article detailing John's discovery of white-tailed prairie dogs (WTPDs) in the Arapaho National Wildlife Refuge, Colorado, attacking and killing Wyoming ground squirrels (Urocitellus elegans). This interspecific (between different species) killing had never been observed before in this species, and is the first well-documented research on interspecific killing among herbivores.

It was clear to John and the team during the early stages of their research on WTPDs in Arapaho (conducted from 2007-2012) that there was competition between the prairie dogs and the Wyoming ground squirrels. Chases and fights were not uncommon, with the aggressor typically being a prairie dog unhappy with a ground squirrel entering her territory (most aggressors were lactating female prairie dogs). It did not take long before John and the team realized the hostilities were often escalating into fatal encounters.

Like white-tailed prairie dogs, Wyoming ground squirrels are burrowing, colonial, diurnal, and herbivorous rodents. Where their ranges overlap, prairie dogs and ground squirrels share habitat and coexist in nearby or adjacent territories. Often they are difficult to tell apart, especially as babies, but as adults Wyoming ground squirrels are approximately half the size of their prairie dog cousins, weighing up to 500 grams as compared to the WTPD's 1100 gram max.

The relatively longer black-tipped tail of the Wyoming ground squirrel can be used to differentiate it from the white-tailed prairie dog. ©John Hoogland 2011

Wyoming ground squirrel juveniles look nearly identical to white-tailed prairie dog juveniles. ©John Hoogland 2011

Female white-tailed praire dog RACR (Ring Around the Collar, Rear legs) faces off with a Wyoming ground squirrel. ©John Hoogland 2011

A Wyoming ground squirrel mother defends her baby (background) from RACR. ©John Hoogland 2011

Female prairie dog RACR leans over the body of a juvenile Wyoming ground squirrel she has just killed, while the agitated mother looks on. ©John Hoogland 2011

Prairie dog male 42 leans over a juvenile Wyoming ground squirrel he has just killed. ©John Hoogland 2011

Blood is visible on 42's face from killing a juvenile Wyoming ground squirrel. ©John Hoogland 2011

Prairie dog 2RS (double Racing Stripe) investigates the carcass of a juvenile Wyoming ground squirrel she has killed. ©John Hoogland 2012

The fresh wounds on the carcass of the juvenile Wyoming ground squirrel are evident. ©John Hoogland 2012

2RS surveys her surroundings standing over the carcass of a juvenile Wyoming ground squirrel. ©John Hoogland 2012

A lactating female prairie dog holds a dead juvenile Wyoming ground squirrel in her jaws. This image was featured in the National Geographic article featuring John and Charles Brown's research. ©John Hoogland 2012

The prairie dog makes sure the juvenile ground squirrel is dead. ©John Hoogland 2012

The carcass of a juvenile Wyoming ground squirrel lays abandoned. White-tailed prairie dogs do not typically cannibalize their ground squirrel victims. ©John Hoogland 2012

After an attack by a prairie dog, this Wyoming ground squirrel mother transfers her surviving offspring to a new, potentially safer, burrow. ©John Hoogland 2011

A female Wyoming ground squirrel cannibilizes the carcass of a dead juvenile. This behavior was not well-understood. ©John Hoogland 2011

Carcasses are examined and photographed for the record. ©John Hoogland 2012

John and colleague Charles Brown wrote of their discovery in a groundbreaking 2016 paper for the Royal Society. In it, they discuss the nature of interspecific killing, and explore the motivations and reasons behind what they observed among WTPDs and Wyoming ground squirrels in Arapaho. From 2007-2012, John and the squad observed 101 killings of ground squirrels by WTPDs. Aggressive lactating females were responsible for 79% of those killings. No murders of prairie dogs by ground squirrels were documented during that time. Unlike the murder of conspecific prairie dog offspring (see our INFANTICIDE page), the killing of a ground squirrels was not typically followed by consumption of the carcass (although a small amount of consumption occasionally occurred). Evidence showed, however, that the overall fitness (survivorship and number of offspring) of the killer prairie dog was greater than it was for non-killers. This is attributed to the decrease in competition for forage, showing that the two species' needs and competition for resources are significant where they share habitat. Being closely related to prairie dogs, and exhibiting much of the same niche behaviors, Wyoming ground squirrels and their offspring compete with prairie dogs for forage and territory, two key resources for suitable habitat. Competition for these resources compromises each species' ability to thrive, reproduce, and sustain generations of a population in the same area.