Genetic Research

Red and Grey squirrel Genetics

genticsIn 1998 there were only 30-40 red squirrels remaining on Anglesey. These formed a single isolated population in the eastern part of Pentraeth forest.

A comparative analysis of hair samples taken from the forest population and material collected from island specimens living within broadleaved woodland sites on Anglesey twenty years ago showed that the island has lost much of the genetic diversity which was once present. By the late 1990s only a single haplotype (in simple terms one female bloodline) remained and was shared by all the animals in the Pentraeth forest population.

Download the BBC News Report on Welsh red squirrel genetics

Download the Conservation Genetics Paper (2005)

This historical research also revealed that there were several red squirrel bloodlines that were unique Wales. These genetic types have, to date, not been found anywhere else in the UK, but in 2011, studies revealed that an animal imported from the European mainland had a similar bloodline.

The red squirrel population on Anglesey has been bolstered with a series of reintroductions. Hair samples were collected from many animals that were used in the release program and genetic profiles were created. These studies revealed that the reintroduction projects involved a genetically rich and diverse range of animals.

In 2010, the Wildgenes Lab at Edinburgh Zoo screened hair samples collected from 100 red squirrel samples that were collected from sites across the island. In the single largest red squirrel genetic study in the UK patterns of gene flow on the island were revealed.

The key findings were:

1. That there had been an increase in the genetic variation on Anglesey.

2. That the number of bloodliines had risen from one to six since 2002/3.

3. That animals had dispersed into Pentraeth forest from adjacent reintroduction sites.

4. That Newborough forest contained the largest single red squirrel population and that genetic types not reintroduced there had arrived through red squirrel dispersal.

5. It was recommended that additional hair sampling takes place and to that end in 2011 and 2012 the Trust aim to collect 200 red squirrel hair samples.


In 2010 and 2011 the Trust also collected 50 grey squirrel hair samples from Anglesey and the Gwynedd mainland. These, along with an archive of 60 hair samples collected from the island in 2007, will allow researchers in London to measure the genetic diversity in the grey squirrel populations in this part of the North Wales coast and to gauge how isolated Anglesey is from the mainland populations.


Center-parcs-pox-1Grey squirrels carry a deadly virus to which they appear immune. When the Squirrelpox virus infects native red squirrels it causes very severe symptoms and ultimately death. The disease is characterised by skin lesions on the face, mouth, feet and anus; these open sores become infected by bacteria and the condition typically leads to death in 2-3 weeks after first infection.

Large proportions of grey squirrels carry the virus and it is not uncommon to find 60-70% of greys have been infected. The presence of this virus is a major reason why grey squirrels should not be allowed to live in areas with red squirrels.


AdenovirusAdenovirus has been found in both grey and red squirrels on Anglesey. It is unclear if it causes pathological infection in grey squirrels or whether it is passed from one squirrel species to another. What is clear though, is that dead red squirrels are frequently found to have the virus present, and in many cases they show signs of illness associated with the infection.

In 2005, adenovirus was associated with significant numbers of deaths in a red squirrel reintroduction being carries out in Newborough forest. It was subsequently found to be present in 2007 and screening detected infections in animals living elsewhere on the island.

The disease causes lesions in the intestines and severe diarrhoea.

Other causes of death

road_signs1. Road Traffic

Every year we find between 10 and 15 red squirrels that have been killed on the road. The bodies are collected and sent for Post Mortem and viral screening. These protocols have revealed several cases of animals carrying disease as a subclinical infection; in other words they showed no symptoms but were infected.

2. Domestic Cats

Domestic cats very occasionally catch and kill red squirrels. We have had records of predation of red squirrels from Wern y Wylan and gardens in Menai Bridge. Once again we have sent the bodies away for analysis and they have provided material for genetic research.


There are many publications relating to disease in red squirrels and we will provide those most relevant to North Wales below:

Adenovirus in Anglesey grey squirrels – Download PDF

Adenovirus infection of red squirrels (UK) – Download PDF

Adenovirus in Angelesy red squirrels – Download PDF

Mortality in red squirrels (UK) – Download PDF

Newborough forest red squirrel reintroduction report – Download PDF

Report dead or sick squirrels


Telephone 07966150847

In the event that a sick or dead red squirrel is found on Anglesey or in Gwynedd please contact us immediatly.

If the body can be collected, please use gloves and place the remains in a plastic bag. We will then collect from you and pass to our veterinary pathologists for post mortem examinations and viral screening.