Purple Gallinule

Moorhens, sometimes called marsh hens, are medium-sized water birds that are members of the rail family Rallidae. They constitute the genusGallinula. They are close relatives of coots, and because of their apparently nervous behavior (frequently twitching tail, neck and grinding their backs) are sometimes called "skitty coots". Often, they are referred to as (black) gallinules.

A few species from the Australian region, sometimes separated in Tribonyx, are called native-hens. Tribonyx is better considered a subgenus however as the differences are not very striking and mainly plesiomorphic. The native-hens differ visually by shorter, thicker and stubbier toes and bills, and longer tails that lack the white signal pattern of typical moorhens.

Source: http://www.wikipedia.org/