Scientists are unravelling the secrets of red and grey squirrel competition

New research, published in the Journal of Medical Microbiology, looked to understand more about the mechanisms by which grey squirrels are able to gain an advantage over red squirrels. Chris Nichols, Conservation Evidence Manager at the Woodland Trust, and co-author of the study, said:

"The more we know about grey squirrels, the more equipped we're going to be in the future to tackle the threats they pose to red squirrels and our native trees, which is one of the biggest problems for forest conservation in the UK."

Grey squirrels are an invasive, non-native species introduced from North America to sites in Great Britain and Ireland between 1876 to 1929. They out-compete the native red squirrels and multiply thanks to various traits including their ability to access a broader range of food sources including the bark of UK broadleaved trees. This causes significant damage to the trees, and is a behaviour that, prior to this research, was not completely understood.

To learn more about what gives grey squirrels an edge over red squirrels, researchers collaborating from the Woodland Trust, University of Surrey, University of Bangor and the Animal and Plant Health Agency analysed the gut microbiota of the two species. The diversity and abundance of the microbes that make up the gut microbiota (microbes living within a particular environment -- in this case the squirrel gut) is often an indicator of the diet, level of health and immunity of an individual.

Researchers sampled bacterial DNA from the gut contents of red and grey squirrels and performed DNA sequencing to identify the bacterial groups present in the two species. They then compared the results to identify any key differences.

They found significant differences in the diversity of gut bacteria between the two types of squirrels, with grey squirrels having a more diverse range of microbiota in their gut.

Lead author of the study Professor Roberto La Ragione, Professor of Veterinary Microbiology and Pathology at the University of Surrey, explained: "Red squirrels are now an endangered species in the UK. Not only are grey squirrels larger and more robust than red squirrels, we have now identified a significant difference in their gut bacterial microbiota, potentially giving them another advantage over reds."

This increased diversity in the grey squirrel gut microbiota could indicate improved general health and immunity compared to red squirrels. It could also reflect the grey squirrel's broader diet, but crucially the difference between the two sample groups provides researchers with valuable information on the way in which grey squirrels are able to access a broader range of resources.

Researchers also identified the presence of oxalate-degrading bacteria in the guts of grey squirrels which means it is likely that they can digest calcium from tree bark and may explain the destructive bark stripping behaviour of the grey squirrels.

As this research was a sample of only UK red squirrels researchers hope that future research could look to mapping the gut microbiota of other native red squirrel populations across Europe to understand more.

Chris Nichols is optimistic about the implications of these findings. "More research needs to be done to further understand the relationship between red and grey squirrels and their gut microbiota, but perhaps in the future we could develop this research into methods that could promote healthy gut bacteria in red squirrels or new ways of preventing squirrels from damaging trees."

Professor Ian Brown OBE, Animal and Plant Health Agency Director of Scientific Services, said: "These findings will help further our understanding of the impact grey squirrels have on the UK's red squirrel population and our vitally important trees and forests, which will in turn help us understand how best to protect them in the future.

"I am proud of APHA's important work on this issue in partnership with the Microbiology Society, Woodland Trust, University of Bangor and the University of Surrey."