A new hope for grey squirrel management – fertility control research update

Kay Haw, UKSA Director

The UK Squirrel Accord (UKSA) partnership is fundraising for research into an oral contraceptive to tackle the negative impacts the invasive non-native grey squirrel causes to native red squirrels and broadleaf trees. As thousands of trees are planted during National Tree Week 2019, we celebrate our success towards developing a new method to help protect those trees from grey squirrel bark stripping damage.

The research into the immunocontraceptive is being carried out by the well-respected Animal and Plant Health Agency (APHA). Researchers are working to turn a proven injectable formulation into an oral contraceptive that will be delivered to grey squirrels via food in a species-specific feeding hopper. Progress at the end of the second of the five-year project is good and hopes are high that this innovative work will provide an effective, less labour intensive, non-lethal method to manage grey squirrels.

Highlights at the end of the second year of research:

  • 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.
  • In collaboration with the British Association for Shooting and Conservation (BASC) and the Deer Initiative, a volunteer-led trial was conducted to test food uptake by grey squirrels in a larger wood (30 hectares). Early analysis shows results are very similar to those obtained in summer in the trials in smaller woods. It also demonstrated the feasibility of volunteer groups successfully deploying the hoppers in the field in the future.
  • Physiological indicators of reproduction in grey squirrels were identified. These indicators will be able to show the effectiveness of the contraceptive vaccine.
  • Work is ongoing to optimise the formulation, dose and frequency of dosing required to turn the injectable vaccine into an effective oral contraceptive. These trials are carried out in collaboration with international groups of researchers at the forefront of research and development in this area.
  • Based on camera traps, a method was developed to estimate the number of grey squirrels in a woodland. This provides end-users with a tool to assess the effort required to significantly reduce or eradicate grey squirrels from a given area.
  • A mathematical model was built to quantify the effects of fertility control, applied on its own or after a period of culling, on grey squirrel numbers. 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.

The oral contraceptive research offers a real opportunity to halt grey squirrel population growth and reduce their numbers and negative impacts. UKSA still needs to raise £250,000 to complete the project. Anyone wishing to support the research can donate online via the UKSA website, where there is also further information on the work: www.squirrelaccord.uk/donate

Further information:

  • The UK’s grey squirrel population is around 2.7 million and rising – as current management methods fail to reduce their numbers. Introduced from North America to England and Ireland between 1876 and 1929, this species quickly established and spread.
  • Grey squirrels cause local extinctions of red squirrels by outcompeting them for food and habitat, and by transmitting squirrel pox virus, which is deadly to reds but not greys.
  • High numbers of grey squirrels also bark strip young, broadleaf trees of 10-40 years old. This damage weakens, stresses and can kill important tree species, such as our highly biodiverse and economically important oaks. This is a serious problem for a country striving to plant more trees for the many ecosystem service benefits they provide, including mitigating climate change impacts.
  • Graham Taylor, Pryor & Rickett Silviculture, recently estimated the long-term cumulative cost of grey squirrel damage to the hardwood timber trade to be over £22.5bn over the next 150 years. This is made up of £40m per year lost to the rural economy and £110m per year spent on imports from abroad by businesses that need the sawn timber that UK woodlands are failing to deliver when trees are damaged.
  • In 2014, a survey of Royal Forestry Society members highlighted grey squirrels as the greatest threat to broadleaf timber production, above the threats posed by tree diseases and deer. One member stated, “I replanted the major part of my woodlands in 1987 with 80% English oak. The bark stripping by grey squirrels over those 26 years has seriously damaged an estimated 40% to 50% of the crop, in many cases fatally”.

UK Squirrel Accord (UKSA)
UKSA is a UK-wide partnership of 37 leading conservation and forestry organisations, Government agencies and companies, with links to voluntary red squirrel conservation groups.

UKSA works collaboratively to preserve the UK’s wooded landscapes and associated biodiversity under the following aims to:

  • Secure and expand UK red squirrel, Sciurus vulgaris, populations beyond current thresholds
  • Ensure UK woodlands flourish and deliver multiple benefits for future generations of wildlife and people

UKSA is a diverse partnership that represents a range of sectors as well as viewpoints. Communications, publications, blog posts and other statements and documents made or published on this website or under the name of UKSA in any other location must not be taken as reflecting the views of all or any particular signatories to the Accord.

For further information see our website www.squirrelaccord.uk or email info@squirrelaccord.uk

A frequently asked questions document on the fertility control research is available via our online resources library: https://squirrelaccord.uk/resources/resources_library/

There are also useful images in our online gallery: https://squirrelaccord.uk/resources/image_gallery/

The update information is also available as a blog post: https://squirrelaccord.uk/news/blog/