Scientists design contraceptives to limit Grey Squirrels

A plan to use oral contraceptives to control Grey Squirrel populations in the UK is making good progress and could soon be put to the test in field trials, say government scientists.

The mass birth control plan involves luring Grey Squirrels into feeding boxes only they can access, using pots containing hazelnut spread. These will be spiked with contraceptives. The project could help eradicate the species in the UK without killing them, says environment minister Lord Benyon.

Could contraceptives limit the UK's non-native Grey Squirrel population? (Jane Rowe).

It should reduce the "untold damage" Grey Squirrels do to woodland ecosystems and native Red Squirrel populations, he says.

The government scientists leading the research say the contraceptive, which makes both male and female Grey Squirrels infertile, should be ready to deploy in the wild within two years.

Grey Squirrels, first introduced from North America in the late 19th century, damage UK woodlands by stripping bark from trees to get at the nutritious sap beneath. The species has flourished in the UK. There are now reckoned to be 2.7 million individuals here.

The animals target young trees, typically 10-50 years old, and favour broadleaf species including oak, beech, sweet chestnut, and sycamore. They can kill or maim trees, leaving scarring that allows an entry point for other tree pests and diseases which can stunt their growth.

The damage they can do threatens the effectiveness of government efforts to tackle climate change by planting tens of thousands of hectares of new woodlands, environment minister Lord Goldsmith has warned.

Grey Squirrels have also driven the UK's native Red Squirrel to the verge of extinction across much of the country. There are thought to be just 160,000 Red Squirrels left in the UK, with only 15,000 remaining in England.

Grey Squirrels are significantly larger and stronger than reds and carry a squirrel pox virus that is deadly to reds but to which they are immune. The traditional way of managing the Grey Squirrel population is by culling them. But Grey Squirrels breed rapidly and populations can recover quickly. A century of culling programmes has failed to reduce the population.