Gray squirrels have their second litter of the year sometime in the middle of summer (July-ish). It takes them quite a while before they're ready to be out and about on their own and they can stay with their mom for about 9 months after being born. By this time of year, those squirrels born in the first litter are finally getting kicked out and have to find new territories. I'd bet that most of the dead squirrels (I-89 is a massacre of squirrels and skunks) are dispersing first years. I've also seen 4 squirrels swimming across the Winooski in the last month, something I've never heard of before. I'm pretty sure this is related to squirrels dispersing. There could also be increased pressure to leave because of the dry tough summer.