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You’re probably thinking, “How hard can it be to breed rabbits?� You’d be surprised.
When researchers began raising New England cottontails in zoos to grow wild populations, they were optimistic, given the reputation of their domestic cousins.
However, only half the pairings produced babies, and many offspring didn’t survive.
But dedicated research supported by the U.S. Fish and Wildlife Service � and led by our state partners and the University of Rhode Island � has revealed secrets to successfully raising these rare rabbits.
Living in the shadows
Though native to the six-state region � and west to New York's Hudson River � New England cottontails are rarely seen. They’re vastly outnumbered by eastern cottontails, which were introduced in the early 20th century as a game species and look almost identical.
Because eastern cottontails are adapted to the more developed, open landscape of modern New England, they’re not only more numerous; they’re more noticeable. New England cottontails prefer young forest � dense, brushy, thicket habitat � which has become rarer as the region’s forests mature. It also hides them from view.
Their nocturnal tendencies make these animals even more enigmatic.
“It's remarkable to me that New England cottontails could literally be living in our backyard, and we know next to nothing about their behavior,� said Justin Richard, assistant professor of animal/veterinary science at the University of Rhode Island.
Rallying for recovery
In the mid-2000s, the Service considered listing the New England cottontail under the Endangered Species Act, due to population declines and loss of habitat. A coordinated response � by state and federal biologists, private landowners, Tribes, foresters, hunters, conservation organizations and others � kept it off the list.
But it’s not out of the woods.
“Because it’s at risk of becoming endangered or threatened, we develop annual work plans using the best available science and engage with partners � particularly the states � to practice strategic habitat conservation,� said Anthony Tur, at-risk species coordinator for the Service’s Northeast region.
Since 2009, we’ve provided $3.6 million for New England cottontail research to state wildlife agencies in Connecticut, Maine, Massachusetts, New Hampshire, New York and Rhode Island through Wildlife Restoration and Competitive State Wildlife grants.
The Wildlife Restoration program grants money to state and territorial wildlife agencies for projects to restore, conserve, manage and enhance wild birds and mammals and their habitat. Since the program was authorized by the Wildlife Restoration Act of 1937, also called the Pittman-Robertson Act, we’ve awarded $17.7 billion collected in manufacturer taxes on ammunition, firearms and archery equipment.
The State Wildlife Grants program helps state and territorial wildlife agencies support species at risk of steep population declines, in hopes of preempting their listing as threatened or endangered under the Endangered Species Act. Since 2002, we’ve awarded more than $1.3 billion through this grant program.
In 2016, the Service created Great Thicket National Wildlife Refuge to conserve New England cottontail habitat. Rather than protecting land in a single location, we aim to acquire up to 15,000 acres of shrubland and young forest habitat from willing landowners in New York and New England.
Anything but easy
A key part of recovery is increasing the size of the wild population through breeding and release into suitable habitat. The New England cottontail breeding program began at Roger Williams Park Zoo in Providence, Rhode Island, in 2011 and expanded to the Queens Zoo in New York City in 2015.
The breeding season for New England cottontails is defined by daylight, with longer days triggering reproductive hormones in late March and shorter ones suppressing them in early August. Under ideal conditions, females can produce three litters in that time span.
“We have a limited window for breeding,� said Heidi Holman, wildlife diversity biologist with the New Hampshire Fish and Game Department and chair of the New England Cottontail Population Work Group. “Shortening the amount of time females aren’t producing is the goal.�
In the early years of the program, male and female rabbits were paired for two-to-three days. There were instances of aggression, and only about half the pairs produced babies, called kits.
“We would actually see them attack each other to the point of injury, and they would have to be removed from a round of breeding,� Holman said.
In 2019, Richard, who’d been teaching an undergraduate class at the zoo, agreed to research New England cottontail breeding.
“We knew next to nothing about their social behavior, about their mating behavior,� he said. “And the lack of productivity was dragging the breeding program down and reducing its overall conservation impact.�
The zoo’s program offered an exceptional opportunity to study the animals� behavior. Richard installed video cameras in the rabbits� pens to collect round-the-clock footage of males and females paired for breeding. He learned those that didn't produce offspring hadn’t mated. It seemed the rabbits were picky about their partners.
Chemistry test
In 2022, graduate student Hannah Petit, working with Richard, designed a study to test this mate-choice hypothesis. She built a pen with smaller enclosures in all four corners. She put a female in the pen and males in three of the corners � with the fourth left empty as a test control � and filmed their interactions over 24 hours.
Petit counted how many times the female visited each male. Next, she put the female in the main pen with each of the three males separately. The female was more likely to mate with the male she had visited the most times during the trial. Females paired with their preferred males had 50% more young than females paired with non-preferred males. That year, the program set a record for number of kits born.
Mate-choice trials have been used every breeding season since Petit’s discovery, and productivity has increased more than 40%. Researchers now know a female is twice as likely to mate with her most preferred male as she is her least preferred male.
But they don’t know what she’s looking for in a mate.
“If we can figure out what she's selecting, we can do an even better job of making sure we put compatible rabbits together so that they make more baby rabbits and we have the maximum conservation impact possible with this program,� Richard said.
Paired males and females exhibit a variety of behaviors � labelled approach, follow, chase, jump-circle, mount � and the female initiates them about half the time.
“There's this behavior called a dash, where one animal will race past another animal, and that is different between successful pairs and unsuccessful pairs, but they do a variety of interesting behaviors that we really need to dig more deeply into,� Richard said.
Poop positive?
After a 24-hour mating session, the male and female rabbits are separated to minimize the risk of stress and harm to the female. The next hurdle is determining whether the female is pregnant. Time is of the essence because, if she isn’t, she should be paired with a male again as soon as possible to maximize her productivity.
It takes two weeks for a female rabbit to appear pregnant or for the pregnancy to be confirmed through physical exam. Ultrasounds and x-rays � common tools used with domestic rabbits � give results sooner, but because the animals in the breeding program are wild, these methods cause extreme stress. Richard is seeking an indirect indicator.
Maybe the scoop is in their poop.
When domestic rabbits first become pregnant, sex hormones like progesterone spike in their blood. Richard is researching whether pregnant New England cottontails exhibit a similar hormonal surge that's measurable in their feces, which can be collected without interacting with the rabbits.
“We’re assuming they’re like all other rabbits and all other mammals, but there are some nuances we need to work through,� he said.
It even could be as simple as snapping a picture.
“In lots of mammals, when progesterone is high, body temperature is elevated, and these changes might be detectable through thermal imaging,� he added. “We’re planning to explore this more.�
Mama needs her space
Achieving pregnancy wasn’t the only challenge. In the early years, females were returned to small, laboratory rack pens in the same room as males after mating. The mothers weren’t building nests or caring for kits born in provided nests, and kit survival was poor.
“It was glaring maternal neglect,� Holman said. “They were stressed, and they weren't building nests and lining them with hair, as they should.�
It seemed they needed space � to move around and distance themselves from the males.
In 2014, thanks to funding from the Service, the breeding facility was expanded to include larger, outdoor pens and separate rooms for males and females.
“Now, the mothers are building big, beautiful nests and hiding,� Holman said. “And the survival rate is going way up.�
Some adult rabbits now spend the winter in outdoor pens. Researchers hope exposure to natural light and temperatures might trigger earlier release of reproductive hormones and lengthen the breeding season.
Parents in their prime
Anyone who breeds animals, whether rabbits or race horses, knows the quality and health of the parents matters. From the start of the breeding program, adult New England cottontails were trapped in the wild, brought into the breeding program for a couple of years, then returned to their home sites. The program's success rests on choosing the best adults.
“What we're finding is that not all wild animals are equal,� Richard said. “They've all had their own experiences that might shape their health and well-being and that influence their ability to reproduce.�
But how to know what a wild rabbit has been through? Hormone levels can help here, as well.
Stress hormones due to poor diet or living situation show up in blood and feces relatively quickly, giving a short-term record of stress � up to a few days. But they’re also incorporated into hair and fur, offering a long-term picture of an animal’s health.
Richard is testing how to measure hormone levels over the length of a strand of fur, to predict which rabbits will be most productive in the breeding program.
Endless opportunities
Richard finds working with the breeding program gratifying, as a researcher and as a professor.
“It's been amazing to see your research have immediate conservation implications,� he said. “There are actually numbers: We're making more animals, and they're supplementing wild populations. You can't have a more direct impact on the conservation of the species.�
He shares that enthusiasm and opportunity for real-world research with his students. Since 2019, more than 40 undergraduates have reviewed the mate-selection videos to record interactions between the rabbits, earning academic credit and contributing to conservation. Many have continued to graduate school or veterinary school or taken jobs with state and federal natural resource agencies.
Richard doesn’t expect to run out of New England cottontail research studies any time soon.
“These animals are much more complex than they get credit for; they never cease to surprise me,� he said. “There's an unlimited number of questions that we can ask, and the really exciting thing is this direct link to the conservation program."
