Oral Contraceptives Can Be Used to Limit Gray Squirrel Population in United Kingdom Without Killing Them [Study]

A government-approved technique to reduce the population of gray squirrels is so far working and giving the best results without killing the animals. Scientists have designed oral contraceptives to cut the number of gray squirrels in the United Kingdom (UK) to protect the population of red squirrels.

Environment minister Lord Benyon said gray squirrels are invasive species that could cause "untold damage to the British countryside." Due to the positive results of the trial, government scientists said that it could soon be put to the test in field trials.

(Photo : Pixabay/EliseAldram)
Oral Contraceptives Can Be Used to Limit Gray Squirrel Population in the UK Without Killing Them, Study Reveals

Impact of Gray Squirrels on British Countryside

Gray squirrels (Sciurus carolinensis) are native to North America and were introduced to the UK in 1876, according to Inside Ecology. In a span of 25 years, they were already found around the country and had colonized areas between Argyll and Stirlingshire in Scotland.

They are easily distinguished from red squirrels because of their gray color, short front legs, and long bushy tail. They are also significantly larger than the red squirrel and have belly fur that is always white.

Despite their cuteness, they compete with red squirrels in coniferous woodland and are highly invasive because of their prolific breeding cycle. They can have two litters of young per year, and each litter usually has three. The government has introduced programs to eradicate gray squirrels, but they rarely work as neighboring populations only fill habitats of eradicated squirrels.

Moreover, gray squirrels tend to be more successful than red squirrels because they carry a virus called Parapox that can kill red squirrels. Also, gray squirrels strip the bark of trees to feed on the soft inner layers, causing severe damage.

Control management is focused on improving the habitat for red squirrels to let them colonize an area before gray squirrels can establish their colony. However, this might be difficult to implement in the UK. So, the government has developed oral contraceptives to prevent gray squirrels from increasing.

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Oral Contraceptives for Gray Squirrels

According to the Royal Forestry Society, the financial cost of gray squirrels' damage is estimated to be around $44.2 million (£37 million) annually in England and Wales alone. Additionally, a mature oak can support over 2,000 species. That is why government scientists have been looking for initiatives to solve the problem of gray squirrels.

Lead scientist Dr. Giovanna Massei from the government's Animal and Plant Health Agency (APHA) said that they have been dosing animals with oral contraceptives that are said to be more humane and still effective, BBC reported. They developed a vaccine that prompts the immune systems of gray squirrels to restrict the production of sex hormones that leaves both males and females infertile.

The medication is not permanent, so more tests are still underway to find a longer-lasting drug that can be safely used in the wild. They developed a feeding hopper that only gray squirrels can use. Trials in Yorkshire and Wales showed promising results, wherein 70% of the squirrels visited the baited boxes during the four-day period of the test.

The baits are pots of hazelnut paste that gray squirrels find irresistible. It is laced with the new contraceptive that could bring the gray squirrel population to the brink of extinction in some places and eradicate them before they could re-immigrate. If their work is successful, it will help control the population of other invasive species, such as rats, mice, deer, and wild boars.

The research is funded by the UK Squirrel Accord (UKSA), a partnership between forestry and conservation organizations in the country. UKSA director Kay Haw noted that the new method is an important addition to the non-lethal methods of managing gray squirrels.