Oral contraceptives for squirrels work, research has found, and the Government hopes they can be used to reduce populations in the UK.
Gray squirrels are an invasive species in the UK, introduced from North America in the 1870s. They pose a problem for wildlife, including the endangered red squirrels they outrun. They also carry a disease called squirrel distemper, which doesn’t affect them but can kill reds.
They were originally used as an ornamental species to decorate the gardens of stately homes before the damage they caused was realized and their release was banned in the 1930s.
Gray squirrels are also a threat to trees, stripping their bark and weakening them. They are a particular problem for deciduous species, including oak, which are ecologically important because they support so many other species. The UK is thought to be home to around 3 million of the invasive rodents.
Scientists are trying to find ways to keep the gray population down and now positive results have been published by the UK Squirrel Accord after a trial of oral contraceptives that could be used to stop the mammals from breeding.
The contraceptive is manufactured by the Animal and Plant Health Agency (Apha), with further testing carried out to ensure it is safe and effective.
To stop other species from ingesting the drug, the scientists designed a special feeding hopper. There is a weighted gate that will exclude most other wildlife while allowing more than 70% of the local gray squirrel population to access and eat from them.
Apha is testing different methods of keeping red squirrels away from feeders so that contraceptives can be placed in areas where both squirrel species are present. So far, research has shown that body weight can be used to distinguish between grays and reds. No oral contraceptives were used at this stage of the study.
Environment Secretary Richard Bennion said: “The gray squirrel is an invasive species that is causing untold damage to the British countryside where these pests continue to destroy our newly hatched broadleaf trees such as oak, stripping bark and disrupting the delicate balance of nature and biodiversity, while reduces our ability to deal with climate change.
“That’s why we continue to support the UK Squirrel Accord and Apha, as this important oral contraceptive research shows promising signs that it could help to eradicate the gray squirrel in the UK in a non-lethal way, as well as help restore our favorite red squirrel. “
Other methods used to try to reduce gray squirrel numbers include releasing pine martens into certain forests. These predators scare and eat gray squirrels. Shy martens, however, will not colonize urban areas that are gray squirrel strongholds, so as long as forests continue to be populated by gray squirrels from the city, other methods – including contraceptives – will be needed to contain populations.
Gideon Henderson, Chief Scientific Adviser at the Department for Environment, Food and Rural Affairs, said: “Fertility control can be an effective method to complement other approaches to wildlife management. This … study aims to produce an immunocontraceptive that can be administered orally to gray squirrels via a species-specific delivery mechanism.
“This innovative research has great potential to provide an effective, easily applicable and non-lethal method of managing gray squirrel populations.” This will help red squirrels – native to the UK – to expand back into their natural habitats, as well as protecting UK forests and increasing biodiversity.”
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