Flightless bird that require a significant amount of overall metabolic energy, ratites decrease their basal metabolic rate and conserve energy. A study looking at the basal rates of birds found a significant correlation between low basal rate and pectoral muscle mass in kiwis. On the contrary, flightless penguins exude an intermediate basal rate. This is likely because penguins have well-developed pectoral muscles for hunting and diving in the water. For ground feeding birds, a cursorial lifestyle is more economical and allows for easier access to dietary requirements. Flying birds have different wing and feather structures that make flying easier, while flightless birds'
Birds of Australia tail for rapid changes of direction. In consequence, the unrelated birds that fill that role in the Americas and in Australia look and act as though they are close relatives. Australian birds which show convergent evolution with Northern Hemisphere species: Australian birds can be classified into six categories: For comprehensive regional lists, see: For Australia's endemic species, see: Other regional, state and island bird lists: National organizations Australian regional and state organisations Important regional references include: Full-coverage field guides in print are as follows, in rough order of authority: Birds of Australia Australia and its offshore islands and territories have