Red Squirrels are very vocal. They bark at intruders, including humans, and can bark continuously for more than an hour if they are annoyed. They also chatter, especially to stake out a territory and protect their stored food supply (conifer cones, which they harvest in great numbers) from other squirrels. They are especially noisy during the breeding season, when they chase each other through tree branches making a distinctive call that sounds almost like the buzz of cicadas. They readily nest in attics and cabins, and are trapped for their fur.

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account