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Revealing insights into squirrel numbers

A new study published in the Journal of Applied Ecology has revealed insights into the changing numbers of non-native grey squirrels and red squirrels.

The study conducted at Queen’s University in Belfast took place across 332 sites in Northern Island. Camera traps were set up at each site and data collected on the co-occurrence of grey squirrels, red squirrels, and pine martens within each region. Using this data, the team was able to predict the future distribution of the three species.




On the whole the results showed a decline in non-native grey squirrels, and a relative increase in red squirrels. This is explained by the recent increase in pine martens and the fact that grey squirrels have been shown to be more vulnerable to predation by pine martens than red squirrels as red squirrels are better at ‘sniffing out danger’. There were however variations between sites.

Notably, heightened grey squirrel populations were more common in the green areas of towns and cities because pine martens are forest specialists and therefore unlikely to be present and predating in these urban areas.




The impacts of grey squirrels are far-reaching, not least because of the consequences of the competition and disease with red squirrels but also the impact on other wildlife such as birds. Indeed, according to estimates from the British Trust for Ornithology, Britons spend between £200m and £300m a year on bird-feeding products, and 44% of feeders were frequented by squirrels. Birds are therefore missing out on significant proportions of food put out for them.

What is more, the research points out that without immediate action, grey squirrels may develop novel genotypes enabling them to avoid pine martens more successfully, allowing them to spread out from urban areas and threaten red squirrels with extinction.




As aptly put by Joshua Twinning, the lead author of the research, ‘As the pine marten does not occupy urban areas anywhere within its European range, it is not likely to be the sole solution to the invasive grey squirrel. If action is not taken to support the pine marten in the long run, we may see a reversal of their current success and doom our native red squirrels’.

Additional actions must therefore be taken in order to control invasive grey squirrel populations – one solution being to increase native woodland cover.

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