If you buy from a pet shop, make sure the animals have been kept in same sex groups and that the staff can show you the difference between males and females. (bluecross.org.uk)
Children play primarily in same - sex groups of friends, and expect more stability in their friendships. (psychology.jrank.org)
During migration they often travel in small groups and can be quite affectionate with each other, often travelling in mixed sex groups. (discovervancouverisland.com)