We call them red squirrels, but they're actually American red squirrels, North American red squirrels or chickarees, and a type of pine squirrel. They are not the same as the red squirrels found in the UK, and they're much smaller than the grey squirrels which (grey or otherwise) are our typical city squirrels. These little guys are 7.1-8.8 oz (200-250 grams) - small. When grey squirrels move into an area, these much smaller ones are displaced.
The red squirrel is an opportunistic eater. It feeds mainly on the seeds of conifers, and seeds, nuts, buds, flowers, bark, mushrooms, insects, eggs and even the young of other small mammals. Although they are skittish little creatures, they are bold enough to take peanuts from your hand and appear to chastise you with a burst of their chatter when the bird feeder is empty!
After a gestation period of 34 days, squirrels produce a litter of 2 to 7 babies, usually nesting above ground in the crooks or hollows of trees. They might even have several nests and move their young around. The mother squirrel nurses the young, called pups, kits, or kittens, for approximately 70 days even after they emerge for the nest at around 42 days.
Red squirrels don't hibernate. They make an elaborate system of tunnels through the snow and they spend most of the summer accumulating food for their winter caches. Like most squirrels, they are quite the acrobats!
References
American red squirrel - wikipedia
Tamiasciurus hudsonicus - Red Squirrel
Images
Photos from the iPad of 
@kansuze