The Distribution Of Grey vs Red Squirrels In The UK & Ireland Between 1945 & 2022

The map above shows the distribution of Grey vs Red Squirrels In The UK & Ireland Between 1945 & 2022.

I’m not 100% sure of the original source of the map a version with 1945 & 2010 can be found on Research Gate here, and I found this version on reddit.

If you created this version of the map please do get in touch so I can provide proper credit.

In the meantime here’s what happened and why:

The story of red vs grey squirrels in the UK & Ireland

The red squirrel (Sciurus vulgaris) is native to the UK and Ireland and was once widespread across forests and woodlands.

• Thrived for thousands of years with no major competitors
• Adapted to native tree species like oak, hazel, and Scots pine
• Populations were stable up until the 19th century

Arrival of grey squirrels (the turning point)

The grey squirrel (Sciurus carolinensis) was introduced from North America in the late 1800s.

• First introduced to estates in England as a novelty species
• Quickly spread into the wild
• By the 20th century, populations expanded rapidly across England, Wales, and parts of Ireland

Why greys outcompeted reds?

Disease: squirrelpox virus

• Grey squirrels carry squirrelpox virus with little harm to themselves
• Red squirrels are highly vulnerable, infection is often fatal
• This caused rapid red squirrel declines wherever greys arrived

This is considered the single biggest factor in red squirrel collapse.

Competition for food

• Grey squirrels digest acorns (especially unripe ones) more efficiently
• Reds struggle with these, especially in broadleaf forests

Result:

• Greys dominate oak woodlands
• Reds are pushed into conifer forests, where greys are less efficient

Size and adaptability

• Grey squirrels are:
  • Larger and stronger
  • More adaptable to urban and fragmented environments.
• Reds are:
  • Smaller
  • More specialized and sensitive to habitat change

Habitat change (human impact)

• The UK and Ireland saw increases in broadleaf woodland and urban parks
• These environments favour greys over reds

What happened over time

In Great Britain

• Reds disappeared from most of England and Wales
• Survive mainly in:
  • Northern England
  • Parts of Scotland
  • Offshore islands (e.g., Anglesey)

In Ireland

• Similar pattern:
  • Greys spread widely
  • Reds declined sharply
• However, red squirrels are recovering in some areas due to control programs (as seen on the 2022 map)

Conservation efforts today

Efforts to save red squirrels include:

• Grey squirrel control programs (culling, fertility control trials)
• Habitat management (favoring conifer forests)
• The surprising role of the pine marten:
  • Native predator recovering in Ireland and Scotland
  • Prefers hunting grey squirrels → indirectly helps reds rebound

In simple terms

• Grey squirrels didn’t just “compete” — they changed the rules of the ecosystem
• They brought disease, outcompeted reds for food, and thrived in human-altered landscapes
• Red squirrels now survive mainly where greys can’t easily dominate.

What do you think?