Safer-at-home means more neighborhood walks — and that means more urban wildlife watching. Over the summer, a new virus affecting rabbits appeared — rabbit hemorrhagic disease virus 2 (RHDV2) — but, as you may notice on your stroll, the cottontails in Northern Colorado are hopping in abundance this winter.
The virus is extremely lethal, killing 70-100% of infected animals, and it spreads easily through contact with the tissue or feces of infected or dead rabbits.
Over the fall, a few cases continued to be reported each month, but, “so far we’re not really seeing a hotbed that keeps spreading,” said Karen Fox, wildlife pathologist for Colorado Parks and Wildlife (CPW).
CPW is urging anyone who finds a dead rabbit to report it — not only to track the disease, but so the carcass can be properly disposed of and limit the virus’ spread.
The cottontail population is fine in large part because, well, it’s large.
"Obviously this disease is killing cottontails, but they’re just so prolific, they can replace themselves really fast," said Fox.
Diseases in strong, proliferating populations — like cottontail rabbits — do not threaten an entire species, but if this disease transfers to other species that exist in smaller populations, that could be a concern.
The virus has been observed in domestic rabbits, cottontail rabbits and jackrabbits, which are a type of hare. But Fox is concerned that it could be transmitted to more wild species like the snowshoe hare, which are in the same family as cottontails and jackrabbits.
Snowshoe hare typically live at higher elevations than Front Range-dwelling cottontails, but the virus can survive in carcasses or feces for up to three months. A hiker or pet who comes into contact with a dead rabbit could unknowingly transport the virus into snowshoe hare territory.
No cases have been reported in snowshoe hare yet, but “our snowshoe hare are pretty much the only prey for lynx,” said Fox.
Lynx, a wild cat related to bobcats, were reintroduced to Colorado in a decade-long effort from 1997-2007. Now, 13 years later, we still have lynx in the state, but their survival is directly dependent on the abundance of snowshoe hares.
Here’s why: the lynx/snowshoe hare relationship is a classic example of a predator-prey interaction cycle. “It’s taught in introductory biology,” said Fox. Lynx subsist solely on a diet of snowshoe hare — so when the hare population is impacted, the lynx population follows.
“The hare population goes up and then the lynx population comes up and then the hare population goes down, you know, and it’s that follow the leader thing,” explained Fox.
People may think that cottontail and fox populations are linked — like lynx and snowshoe hare — but, they’re not.
“I get questions every year about foxes and rabbits and what’s that cycle?” said Fox.
Foxes eat cottontails, but their populations aren’t as interdependent because foxes aren’t such fussy eaters, explained Fox (who only enjoys rabbit as dinner conversation). Foxes are omnivores and enjoy meals of mice, berries and even earthworms. Since their food networks are more dynamic, foxes are less vulnerable than more picky eaters like lynx.
We typically think of larger predators eating smaller prey, but sometimes the predator is microscopic, like a virus.
While the cottontails hop throughout our neighborhoods this winter, be on the lookout for dead rabbits and report any that you find to CPW. A quick phone call could help ensure the health of more than just your neighborhood cottontails.