Sugar gliders are very sociable animals and must be kept in a minimum of a pair. A lone glider can be prone to serious self-multilation that can even lead to death. It is vital therefore to keep a keen eye on a lone glider and match them up with a new friend as soon as possible.
It is important to regularly handle your sugar gliders, with many owners using bonding pouches or bags to help this. A sugar glider that has not been regularly handled may display behaviour known as "crabbing" where they give a surprisingly, loud warning call - example below.
Sugar gliders can be very vocal, and not very sociable in the hours they chose this either! the first example below is a sugar glider making a barking call (at 6am) the second is a more disturbed, warning call often known as "crabbing".