Fertility control research

Field trials of the feeding hopper by APHA

UK Squirrel Accord is fundraising for research into a fertility control for grey squirrels. This will offer a non-lethal management method to control population densities and support eradication efforts.

The study aims to produce an immunocontraceptive that can be orally taken by grey squirrels through a species-specific delivery mechanism. We have just started the third of the five-year project and an update can be read here.


So far, results from the Animal Plant Health Health Agency (APHA) show that an orally delivered contraceptive was effective in reducing reproduction in rats. APHA will move to testing the contraceptive for effectiveness on grey squirrels.

Tests on a hopper to deliver the oral contraceptive to grey squirrels only are going well. The test bait, without contraceptives, is attractive to grey squirrels and the hopper currently prevents almost all but the very largest red squirrels from accessing it.

Hair of squirrels, photographed under UV light, that ingested bait containing the marker Rhodamine B by APHA

Rhodamine B is used as a marker. It is consumed as part of the bait and is incorporated into the animal’s hair. This causes the hair to fluoresce under UV light and identifies squirrels that have ingested the bait.

Further work will now be done to assess the amount of bait eaten per visit, monitor bait uptake in areas with different squirrel densities and refine the hopper to minimise potential bait uptake by non-target species.

Defra is complementing this research by creating a model to predict grey squirrel densities in woodlands to guide management efforts, assess how large a buffer needs to be to prevent reinvasion and predict the rate of reinvasion to areas if management stops.

Supporting the research

UKSA is fundraising for the fertility control research and has succeeded in raising £842,000. To complete the research, a further £250,000 needs to be secured. If you are interested in supporting this important work please contact info@squirrelaccord.uk or donate online.

Further reading

UKSA fertility control research FAQs 2019 - research - UK Squirrel Accord

A new hope for grey squirrel management - fertility control research update blog - 2019

APHA Science Blog: Plight of the red squirrel - 2018