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 are now into the third of the five-year project and hopes are high that this innovative work will provide an effective, less labour intensive, non-lethal method for managing grey squirrels.


The impact of Covid-19 has been to extend the time needed to complete the research objectives for year three of our five-year programme to September 2021.



Why use fertility control?

Across the world, fertility control is being seen as a complementary and alternative method for wildlife management. Watch this Botstiber Institute for Wildlife Fertility Control video of an interview with Dr Giovanna Massei, a leading scientist in this area, to find out more…




UKSA progress

The Animal Plant Health Health Agency (APHA) is currently trialling three different methods of reducing fertility and creating an effective product that can be taken orally. The best of those being tested will be taken forward for further development in years four and five.


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.


In 2019, significant progress was made in understanding how contraceptives could be effectively deployed in the field. Different densities of hoppers were tested to monitor food (without immunocontraceptive in it) uptake by grey squirrel populations in relatively small woods (6-18 hectares). Results suggest that relatively little effort (four days) is required in summer to ensure the majority of grey squirrels access and consume the food that will ultimately contain the contraceptive.


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.


Defra is complementing this research by creating a model to compare different management techniques, 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.


Modelling suggests fertility control applied in conjunction with culling is most effective at eradicating or significantly reducing densities of grey squirrels to numbers low enough to mitigate most of the economic and environmental problems they cause. This does not prevent fertility control being used on its own, but the effects will take longer.



Third year research objectives

Work in 2020 will focus on development of the oral contraceptive, creating a system to monitor the quantity of bait consumed by grey squirrels on each visit to inform the strategy, refining the hopper to minimise potential bait uptake by non-target species and building on the success of working with volunteer groups but on a larger scale. This will involve working with a number of voluntary red squirrel conservation groups in northern England.


Coordinated effort will ultimately be essential for effective roll out of the fertility control in the future. We are exploring the potential to work with projects and partnerships that will enable the oral contraceptive to be deployed at a landscape scale once the research project is completed.



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:



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