What is theme the migration of grey squirrels?

Grey squirrels don't typically migrate in the same way that birds do, moving long distances in search of food or better breeding grounds. They are territorial and will generally stay within their established ranges, which can vary in size depending on factors like food availability and competition.

However, you could say there are themes related to the movement of grey squirrels:

* Expansion: Grey squirrels are an invasive species in many parts of the world, including the UK. Their rapid expansion into new territories is driven by factors like their ability to outcompete native species for food and resources, as well as their adaptability to different environments.

* Dispersal: Young grey squirrels, particularly males, may leave their natal territory in search of their own breeding grounds. This dispersal helps to prevent inbreeding and allows for the establishment of new populations.

* Food availability: Grey squirrels may shift their home ranges seasonally in response to changes in food availability. For example, they may move to areas with more acorns during the fall.

* Climate change: While not a traditional migration, climate change may have an impact on the movement of grey squirrels in the future. As temperatures rise and habitats change, squirrels may need to move to areas with more suitable conditions.

Overall, the movement of grey squirrels is not a "migration" in the strict sense of the word. It is more accurately described as dispersal, expansion, or shifting home ranges in response to factors like food availability, competition, and climate change.