Squirrels To Be Given Contraception To Help Reduce Numbers

Gray squirrels in the U.K. may soon be given oral birth control medication in an attempt to keep the invasive species at bay, as part of a government plan.

Gray squirrels, the common bushy-tailed rodents native to North America, were introduced to the U.K. as curiosities in the late 19th century by wealthy individuals.

Over several decades the squirrels spread prolifically, eventually leading to a ban on their import in 1937 that is still in force today.

But it was too late; the gray squirrel population had cemented itself in the country, posing a threat to the native, smaller red squirrel and causing damage to forestry.

Gray squirrels are a threat to red squirrels due to competition for resources and space, and also because they carry a disease that does not appear to affect grays but often kills red squirrels.

Gray squirrel
A stock photo shows a gray squirrel sitting on a tree stump. Contraceptives are due to be used as a humane way to control their numbers in the U.K. birdsonline/Getty

Now, contraceptives are being introduced as a way to control gray squirrel numbers and help red squirrels recover. A key aspect to the method is that it's non-lethal—after all, the spread of gray squirrels is the fault of humans, not the squirrels themselves, a 2016 study found.

The contraceptive method is being worked on by a team from the U.K. government's Animal and Plant Health Agency (APHA) as part of a five-year development project due to end in January, 2024.

No medicine has actually been placed in the countryside as yet, as the team has first had to develop a method of ensuring that the contraceptives end up being taken by gray squirrels, and gray squirrels only.

On Sunday, the U.K. Squirrel Accord (UKSA) group announced that vital progress had been made in this regard. Experts have developed a feed hopper with a weighted door that should allow over 70 percent of gray squirrels to eat from it whilst preventing most other species of wildlife.

Currently, the hopper is being tested to ensure it prevents red squirrels from feeding from it as well, otherwise it could be counterproductive. Body weight could be used to distinguish between the two.

With research and development ending next year, field trials will follow and it's hoped widespread availability of approved methods will come after that.

"This innovative research has great potential to provide an effective, easily-applied and non-lethal method for managing grey squirrel populations," said Gideon Henderson, chief scientific adviser at the U.K. government's Department of Environment, Food and Rural Affairs, in a press release.

"It will help red squirrels—native to the U.K.—expand back into their natural habitats, as well as protecting UK woodland and increasing biodiversity."

Red squirrel
A stock photo shows a red squirrel amongst some bluebells. The species faces competition and disease from gray squirrels. Ian Groves/Getty

There are an estimated 140,000 red squirrels left in the U.K. compared to 2.5 million grays.

In North America, the prime habitat for gray squirrels is thought to be the deciduous forests in the eastern half of the continent, including mixed forest in southern Canada.

While it may be regarded as an invasive pest in Europe, the gray squirrel plays an important role in dispersing seeds so that trees grow.