Greys at 2.7 million, reds at 287,000: 150 years from one release

A century and a half ago, in 1876, a pair of North American grey squirrels was released into a park near Macclesfield in Cheshire as a novelty, and escaped. The Red Squirrel Survival Trust (RSST) marked the anniversary this week with the arithmetic of what followed: reds, then numbering about three million, now stand at roughly 287,000, while greys have reached 2.5 to 2.7 million.

Why did greys displace reds so completely?

Weight and fecundity, the trust says. At about 500g to the red’s 300g, greys outcompete reds for food and ground, and can produce up to eight kittens in two litters a year. The fatal edge is squirrelpox, which greys carry and transmit while reds die of it within weeks. Only about 39,000 reds remain in England and Wales together, with the balance of the population mostly in Scotland.

What is the damage beyond the reds?

Bark-stripping of oak, birch, beech and sycamore costs about £40m a year, and the Forestry Commission estimates grey damage could cost £1.1bn over the next 40 years, a direct threat to the national ambition to plant 1.5 billion trees. For shoots and keepers, grey control by trapping and shooting remains one of the most useful contributions the community makes to woodland health, and it is what holds local populations down while science catches up.

How close is the contraceptive?

Research funded through the RSST and the UK Squirrel Accord at the Animal and Plant Health Agency is developing an immunocontraceptive vaccine with a delivery system that only greys can access, estimated to be available to land managers in around five years. Models suggest a landscape-scale collapse in grey numbers once deployed alongside traditional control. The work has royal backing: the King, the trust’s patron, was briefed on it at the agency’s York campus in May, when scientists showed hazelnut paste laced with contraceptive delivered through weighted hoppers engineered to exclude the lighter reds.

An RSST spokesman said: “Britain and Ireland’s familiar woodland landscape is at risk from the exponential increase in the grey squirrel population, the virulent disease they carry, and the serious damage they cause to trees. The red squirrel must be allowed to flourish, giving visible proof of the health and viability of our native woods and forests.”

What happens next

The contraceptive programme continues at the Animal and Plant Health Agency with deployment trials ahead, and the trust is urging land managers to keep conventional control running in the meantime. The RSST’s full account of the anniversary is linked below.