Traffic can account for half of red squirrel deaths in some urban populations, study suggests

Researchers are investigating the suitability of urban habitats for red squirrels

Ecologists at Nottingham Trent University have been looking into the suitability of urban habitats for red squirrels and the various challenges and opportunities they face in these environments.

The red squirrel is native to Britain and Ireland but is under serious threat of extinction in these countries because of habitat loss, competition with grey squirrels and a fatal disease called squirrel pox.

They have suffered population declines in several other countries across their range in recent decades.

One of the key findings from the study – which involved reviewing a range of previous evidence and research into red squirrel populations across the UK and Europe – was the significant role that road traffic accidents played in the deaths of red squirrels.

The researchers found that traffic had been responsible for between 20% and 65% of red squirrel recorded deaths in some populations, with studies also showing traffic being accountable for 42%, 43%, 48% and 51% of deaths.

Despite this, the researchers say traffic doesn’t appear to be a limiting factor for red squirrel populations and that urban environments can support higher densities of red squirrels than their typical rural homes.

Studies also showed that there was a seasonal pattern in road traffic deaths with peaks in the autumn, when red squirrels spend more time foraging and hoarding food which could lead to them crossing roads more regularly.

There are also fewer red squirrels in spring and summer, with a post-breeding increase in numbers in autumn and winter.

Evidence also showed that males were more likely to be killed by traffic during the winter months, which is the time they begin looking for sexually active females.

In one study various diseases were responsible for more than two-thirds (34%) of red squirrel deaths, while in others predation from animals ranged from 5% to 25% of deaths, with domestic and feral cats and foxes most likely responsible.

The researchers say that higher densities of red squirrels in urban habitats was most likely due to the widespread and reliable provision of additional food left by people, alongside natural food sources, as well as availability of quality green spaces in urban areas.

Despite the barriers to urban landscapes – such as roads and traffic – red squirrels can still disperse and maintain their gene flow, the researchers say.

“Road traffic accidents do seem to be responsible for a significant proportion of red squirrel deaths in some populations, said Kat Fingland, a researcher in Nottingham Trent University’s School of Animal, Rural and Environmental Sciences.

“Some red squirrel groups have installed rope bridges at traffic accident hotspots to try to minimise the impact of traffic. It is unlikely that traffic is a limiting factor for red squirrel populations, however, and we suspect that ensuring there is enough quality habitat available in urban areas – with suitable natural food sources and nesting spaces – is more important in maintaining red squirrel numbers.

“Diseases can also be a significant cause of death, so monitoring for squirrel pox outbreaks is also crucial, particularly in higher density urban populations where there are squirrels sharing feeders and the disease can spread more quickly.”

Dr Samantha Bremner-Harrison, another Nottingham Trent University researcher on the project, said: “We know that urban areas can provide suitable habitat for wildlife and that different species can adapt well to these environments. Such areas can be suitable for red squirrels too, provided that high quality greenspaces are maintained and suitable measures considered to reduce population mortality and prevent disease outbreaks.

“This is important as growth and intensification is only going to increase alongside the human population.”

Nottingham Trent University’s Dr Samantha Ward added: “This work is really important for the conservation of the red squirrel in England. The more we know about the problems they face, the more we can do to mitigate the issues and hopefully make a positive impact to increase red squirrels in urban areas.”

The research is published in the journal Mammal Review.