The squirrel debate seems straightforward: red squirrels are native to Britain. Grey squirrels are invasive aliens. Reds are endangered. Greys are rampant. The disease squirrel pox threatens reds, while greys are immune carriers. Greys outcompete reds for habitat and food. So greys must be handicapped? Like any ecological relationship, the truth is much more complex and fascinating.
Are we being speciesist? Are reds native, or just longer established? Calling anything ‘native’ is arbitrary: we all invaded at some point, but where do we draw the line? Where humans have previously actively introduced species with consequences we subsequently dislike? Or where the species has arrived through ‘natural’ dispersal? “Red squirrels are thought to have arrived in Britain at the end of the last ice age roughly 10,000 years ago,” along with most other species, as not much can survive an ice age. This contrasts to greys which were introduced by humans from the 19th century.
The loss of the reds’ preferred conifer woodland habitat and food source due to urbanisation placed the population under pressure. Reds prefer conifer woodland, while greys flourish on larger seeded hardwoods, so, even now, woodland conservation that favours deciduous trees may be inadvertently favouring greys.
During the 19th and early 20th centuries, red squirrels were persecuted by gamekeepers, apparently as a scapegoat for any marginal losses of game. Fewer than 120,000 red squirrels remain in Scotland, and only a further 40,000 in the rest of the UK. There are twice as many greys as reds in Scotland and a much higher proportion elsewhere in the UK.
Should we leave the red population to develop immunity to squirrelpox virus as greys have? Let natural selection favour the stronger? Some red individuals have been found with immunity, but generally where they are less stressed. With all the other pressures of human activity they are subject to, leaving it to chance looks likely to eliminate reds. Similarly, humans are too far from offering a vaccine for reds, or indeed contraception for greys. “Grey squirrel contraception is the subject of research, as is the development of a squirrelpox vaccine but these are a long way from being ready for use and may be insufficient on their own.”
We should also challenge whether what is politely called ‘control’ of greys is actually humane. The opposition suggests three methods of grey ‘control’ are used: shooting, poisoning and trapping. The first two are neither humane nor effective and are not used by any official control programme, although there may sadly be local cases, just as red persecution still occurs. Live trapping is used, then the “captured grey squirrels were allowed to venture out from the wire trap into sacking that had been placed around the entrance. The squirrel would then be moved into the corner of the sack and killed by a single blow to the back of the head. This is regarded to be a humane method.” The humanity of any lethal action can be debated, but without grey squirrel contraception, this seems the least worst option.
Are there any other squirrel species involved? Black squirrels are also reported in the UK. Is this another non-native invader? “Black squirrels originate from North America and are the same species as grey squirrels,” merely having a single gene mutation that causes their fur to grow black. Following greys, they were introduced in south-east England early in the 20th century and now interbreed, producing brown-black offspring. However, the black fur gene is dominant so greys are themselves being very slowly overtaken. Sadly, as yet, there is no evidence for my idle speculation that black squirrels may be more prevalent in industrial areas, i.e. more successful for being better camouflaged against soot-encrusted features.
Is there no natural predator? Research has shown the favourable effect of pine martens on red squirrel populations in Ireland suggesting that they selectively prey on greys. More research is underway at “the University of Aberdeen to investigate whether the same effect is occurring in Scotland in areas where the pine marten is recovering.” The pine marten certainly “plays an integral role in a healthy, balanced woodland ecosystem and can be an important predator of pest species, such as grey squirrels.”
What happened to pine martens? Like many predators, their “disappearance was principally a result of predator control associated with the increase in popularity of game shooting coming on top of the loss of so much of Britain’s mature woodland – the favoured habitat of the pine marten.” Gamekeepers are still at it: “the Game & Wildlife Conservation Trust (GWCT), a charity funded by landowners, farmers and sporting interests, wants to launch a trial next year to trap and relocate pine martens, which are protected under law as an endangered species,” on the very shaky grounds that pine martens are responsible for the disappearance of the capercaillie. The disappearance of capercaillies is reserved for shooters.
We can’t undo history, but we can stop persecuting predators and start to reverse the legacy of introducing favoured species with little idea of consequences throughout the ecosystem. Is it viable to leave ecology to find a natural equilibrium through the action of pine martens, buzzards, goshawks or other natural predators?
The effect of predators is difficult to measure, as the distribution of grey squirrels depends on where and when they were released. In Scotland their expansion from such points can be mapped as they are still restricted to areas of the south and east. In other areas of the UK this may be impossible as greys have colonised entire regions. Plus of course greys’ distribution is also affected by their preference for larger seeded hardwood habitat.
The arrival of pine martens does cause a reduction in greys, but they are not simply gone in a gulp: a proportion disperse to neighbouring areas. Thus their removal has to be approached over a wide area and sustained over a long timescale to avoid the vacuum effect. Moreover, reds are not invulnerable to pine martens, despite the appealing image of them out-waiting the pine martens by dangling on the end of pine branches like Christmas tree baubles – “red squirrels have a simple adaptation to pine martens: they are small and light enough to get to the ends of the branches, where the martens can’t follow.”
While Scotland and Anglesey, an island off the north-west coast of Wales, have a clear, concerted, sustained approach, the rest of the UK may struggle to scale up this success, especially while its government is barely engaged. “Defra, the government department responsible for wildlife policies, said a national eradication plan was unfeasible but it did plan to control squirrels on Forestry Commission land.”
It’s not about colour, or longevity, or compatibility with the human wildlife management fashions of the day. The further back you stand, the bigger and more complex the picture you see. The red squirrel is an iconic species, a representative indicator of the health of our ecosystem, allowing us to gauge the extent of its destruction and, hopefully, the success of our attempts to heal that.
1. Saving Scotland’s Red Squirrels, project evaluation report, 2012
2. Saving Scotland’s Red Squirrels, personal communication, 2015
This article is also published at Wildlife Articles.