Red squirrels can be killed by a virus passed on by their grey cousins
The public are being urged to track the UK's red squirrel population to help protect it from a deadly virus.
The Wildlife Trusts charity wants to guard against the threat posed to the UK's estimated 160,000 red squirrels by squirrel pox, carried by greys.
By people reporting sightings of reds during Squirrel Week, which starts later, it hopes to identify areas where protective measures may be required.
These could include culling of grey squirrels, which are more common.
Conservationists say culling is a necessary evil to help preserve red squirrels for the future.
The native red squirrel has been given the highest level of protection under UK law through the Wildlife and Countryside Act.
Its numbers have been declining steadily since the introduction of its bigger and bolder cousin, the North American grey, in the 19th Century.
There are believed to be just 25,000 reds left in England, concentrated in a few pockets including the Isle of Wight, Poole Harbour in Dorset, Northumberland, Cumbria and Merseyside.
A number of organisations across the UK will co-ordinate the week-long squirrel-tracking project, including Save our Squirrels in Northumberland.
It comes down to which is the native species - the one that belongs here - and which is the alien invader
Save our Squirrels
Philippa Mitchell from the organisation said the red species could die out in just 10 years unless action was taken.
Conservationists are hoping to develop a vaccine against squirrel pox within that time period.
Ms Mitchell said more cases of the disease, which does not affect grey squirrels, were spotted every month and the problem was most acute in the autumn.
She said: "The young are moving into new areas at this time of year, so young greys could be moving into areas where they weren't before, and could be taking squirrel pox with them."
The public is also asked to report sightings of grey squirrels so that conservationists can find out if they have invaded areas where red squirrels live.
Ms Mitchell said the only way to deal with the aggressive grey population was to cull them.
She said: "It comes down to which is the native species - the one that belongs here - and which is the alien invader.
"The red is a protected species."