AN oral contraceptive being researched by the UK Squirrel Accord (UKSA) could help protect tree health by halting grey squirrel population growth, reducing their numbers and negative impacts.

Grey squirrels are damaging broadleaf trees and causing local extinctions of the native red squirrel, with the situation being so serious, the UKSA said, that it was part of a key House of Lords debate on threats from tree pests and diseases (13 February 2020) and was directly highlighted by 14 of the 24 speakers.

Intensive bark stripping by invasive non-native greys creates wounds that pathogens can infect. High densities of juveniles can strip bark from the main stem and branches of trees between April and September, with particularly susceptible tree species including oak, beech, hornbeam and sweet chestnut.

Grey squirrels are said to target young broadleaved trees, mostly 10–40 years of age, and repeat the damage year after year if their densities are high and unmanaged.

Lord Gardiner of Kimble, parliamentary under secretary of state for rural affairs and biosecurity, said: “I should also turn to the grey squirrel, how could I not acknowledge the noble Earl Lord Kinnoull and all that he and the UK Squirrel Accord are undertaking. With support from DEFRA, the Accord’s research to develop an oral contraceptive as an effective method for controlling grey squirrel populations is delivering promising initial results. Fertility control does have the potential to reduce grey squirrel populations and the spread of the squirrel pox virus.”

UKSA 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. 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.

The Earl of Kinnoull, chair of the UK Squirrel Accord and Red Squirrel Survival Trust, said: “The UK Squirrel Accord has commissioned a fertility-control project at the Animal and Plant Health Agency, which it is hoped will perfect a suitable active substance and hopper delivery method to allow fertility control to shrink grey squirrel numbers significantly, allowing forestry a chance.”