Over a period of about ten days in September, I visited the Cambridge University Botanic Garden three times. On the first two visits I saw maybe five or six squirrels but on the third visit I saw around fifty young squirrels. Why so many squirrels, so suddenly?
I asked CUGB, and the wildlife experts wrote that in their opinion the reason was that:
Last year was a mast year for oaks. Mast years happen in intervals of round 7-10 years and are years when oaks produce masses of acorns and this is synchronised- so all the oaks in an area will do the same thing. This provides an abundance of food for species like squirrels who then overwinter very well and then are able to breed really well the following year. Now’s the time that lots of young ones are becoming independent and are out and about more. Hence lots of squirrels. When its not a mast year, there are fewer acorns and this is a way that plants can keep their herbivores in check. See this article in the Woodland Trust site, what is a mast year?