Workshop Notes: Determining Breeding Status of Grey Squirrel

Workshop Notes from 3rd May 2018         

The two Red Squirrels United projects in north Wales got together on 3rd May to offer this workshop to volunteers.

Here are some notes taken from the workshop for future reference.

Becky introducing the day

Becky introducing the day

Dreys – general info:

  • It’s not an offence to destroy/disturb a grey squirrel drey, only red
  • It’s an offence to block access to a red squirrel drey or disturb if in use
  • NOT an offence if the drey is not in use but you need to demonstrate that it is no longer in use
  • Some dreys can be clumps of ivy and in tree hollows so you are unlikely to see them
  • Squirrels will chew tree holes to make them the right size
  • Grey squirrel is a cavity-dwelling specialist – more so than reds
  • Locally in Wales our trees are young with fewer cavities which may be having an effect on grey squirrel numbers – keeping them lower than if the trees could support the population
  • In their native NE America, greys use tree cavities as escape routes/refuge from predators such as raccoon and marten
  • In UK it is not an offence if your pet dog chases grey squirrels but it becomes an offence if you deliberately set your dog after it
  • How to tell if drey is in use? Put your hand in and if you get fleas it’s likely to be in use! GS & RS have different fleas. GS arrived in Italy without fleas but now have them and may have caught them from RS
  • Note, fleas live for 2 – 3 days so if there are fleas its likely to still be active/in use
  • Obviously this all becomes difficult if the drey is 60′ up!
  • In situations where you find both GS & RS, they can share the same dreys – not at the same time of course.

    Craig showing a squirrel drey - artificial

    Craig showing a squirrel drey – artificial


  • Mating behaviour – squirrels are promiscuous so it’s difficult to tell who the father is – kits in one litter are likely to have different fathers
  • Mothers and sisters are likely to share dreys especially in cold weather. Relatedness means that if an animal is related it is more likely to share a drey.

Grey Squirrel drey vs Red Squirrel drey:

  • GS slightly larger
  • NOTE: Twigs that make up the drey will be from the tree it is built in so it could be larger just because of the tree species and the twigs themselves!
  • Use of green leaves can be telling – RS rarely bite off the green leaves but GS do. If a drey has green leaves, it may indicate GS.
Looking at camera trap footage in Treborth Gardens

Looking at camera trap footage in Treborth Gardens

Dissection – Determining Reproductive State

  • To measure squirrel, stretch it out and take measurement from tip of nose to base of tail
  • Reproductive state: 1.5cm gap between anus and penis whereas in a female the vulva is close to the anus. Male – testes may be prominent. When active the hair wears away and the area becomes blackened
  • If not active, the testes regress
  • Take samples of spleen as it holds a good source of viral DNA
  • It’s been discovered that GS have an internal parasite which it has brought to Europe and is now infecting RS
  • Female has 2 uterine horns and once it has had young, scarring can be seen
  • 8 teats but never have 8 young so not sure why evolved with 8!
  • If teats are showing it indicates a lactating female and fur is worn around the teats
  • The vulva becomes sealed with pregnant
  • TEETH – molars become blackened over time so if they are white on a squirrel you have caught it is likely to be a young animal
  • 5 – 6 average life expectancy
  • 50% will die within the first year.