When found, one of them has his body over the other protecting it from the cold...or what evil might befall them. They tried to hide in the edger dirt line between the yard and sidewalk. They might be a month old (eyes are open and alert...have some weight to them)
Here's the question: Is this instinct or heroics on the part of the squirrel who covered the other one?
I'd say it was probably trying to stay close and share body heat, not so much protecting. One might've had a personality that was more pro-active and the other more passive though, as these are both valid survival strategies seen amongst most species.
Instinct...always comes to mind with nature...but what if one is the more heroic of the bunch? As Vala Faye stated: some are passive and some are pro-active. What if the pro-active one knew what he had to do...and did it! I find that amazing...on any level...human, mammal, or other creatures. That one steps up to the plate...as a hero...for another!
As an after thought..I've got a feral cat at home who, when she goes to the vet, panicks and flips out..stresses. And, she doesn't normally allow me to touch her. But at the vets..she crawls into my arms.
My point is..in a high-stress environment, you cling and bond with what is familiar..namely your fellow 'nestling'.
So instinctly...she crawls into your arms at the vet...right. Or is it an act that she is consciously aware of? In other words, she decides she needs protecting...so she seeks help.
Ok...I'll come right out and say it. Instinct or not...I believe the one squirrel who decided to protect the other one...whether it was for added body warmth...or to protect against a cat or other varmint on the prowl...is a hero. Whatever the reason, instinct or not...for a little baby, on it's own, to put ones own self interest above the others is quite remarkable!