From the Super Mario Wiki
Birdoroos are a species of Birdos that inhabit Down Under Land. They resemble kangaroos due to the fact that they get around by hopping, and because the adults (most likely just the females) have pouches for carrying their babies. Although Birdoroos will keep to themselves if not provoked, they are also territorial, and will assault anyone who invades their territory with Eggs. Adult Birdoroos also wear Akubra-style hats, although how exactly they obtain them is unknown.
Birdoroos only ever appeared in The Super Mario Bros. Super Show! episode "Crocodile Mario", where they could first be seen hopping around Down Under Land, minding their own business. However, when Mario and Luigi passed by their territory on a raft, an entire family of Birdoroos launched an onslaught of Eggs in their direction, which they barely managed to dodge.