These guys are diurnal herbivores, living solitary lives but for in the breeding season. They live in rocky environments up in the high altitude regions where it gets really cool, but interestingly enough they don't hibernate during winter. Instead they spend a crap load of time prior to winter collecting all sorts of vegetation and stock piling it. Over time it turns into hay, which they can use for bedding, insulation as well as food. What was really cool about the segment was when David Attenborough put down a bouquet of flowers on a rock, with no other vegetation anywhere near by it was no time before the pikas came out and pillaged this precious resource, adding it to their piles.
Here's the clip from Youtube of David unleashing with the pikas!