Grey squirrels were introduced to the UK from the USA in the late 19th century and there has been a subsequent decline in our native Red squirrels. This is due to Grey squirrels outcompeting Red squirrels as they feed more at ground level and can digest acorns. These non-native squirrels also carry a deadly pox which does not affect them but is lethal to Red squirrels.
This is a well-known conservation issue and many strategies have been employed in order to eradicate this invasive species. However, these have all failed and the government has seemingly given up hope as in March this year the 140-year law requiring people to report sightings of the invading species so they could be destroyed was abolished. The future for this species looked bleak with conservation efforts focusing on protecting the few strongholds that this species had left, namely islands where Grey squirrels were yet to invade.
However, a glimmer of hope has been revealed by a 2009 study that highlighted that in some areas of Ireland Red squirrel populations were recovering even in the presence of this invasive species. The most significant and surprising result of this study was that Pine Martens seemed to be the reason for this boom in population numbers. Pine Martens are another native species that has been in decline due to destruction of their habitat and human persecution. Populations of this species have now begun to recover and they have some particular strongholds in Ireland. This study demonstrated that there was a positive correlation between Pine Marten and Red squirrel numbers, which is unusual as Pine martens actually eat these squirrels. However, Pine Martens also eat Grey squirrels and this study suggests that these are the preferred prey as they featured 8 times more frequently in scats than Red squirrels did. This is to be expected as this species is more abundant so numerically more available, but they are also often larger and slower than Red squirrels so they may be the more attractive prey choice. Another important factor is that Grey squirrels haven’t evolved to escape Pine Martens like Red squirrels so may be less efficient at it.
In conclusion, Pine Martens are reducing Grey squirrel populations through direct predation and they may also be having more subtle effects on these squirrel’s numbers. Many studies have investigated the effect of predator presence on prey and the results have included stress-induced reduction in breeding activity, suppressed immunity, changes in foraging behaviour and shifts of habitat to avoid the risk of predation. This reduction in Grey squirrels is the likely explanation for the increase in Red squirrels in these areas. This is a very exciting study as it suggests a potential natural solution is possible to increase Red squirrels numbers and it is by protecting another of our native species. I believe this is an example of nature trying to right itself and we just need to provide some support in order to achieve a happy ending all round.
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