|MadSci Network: Evolution|
There certainly are a lot of flightless birds in Australia and New Zealand. Australia has two kinds of flightless bird, the Cassowary and the Emu. New Zealand has the small, nocturnal Kiwi, a flightless parrot called the Kakapo, and a flightless gallinule called the Takahe . New Zealand was also home to moas, a group of large flightless bird that are now extinct. Your hypothesis that flightlessness in Australia and New Zealand bird is due to what they eat is interesting, and it might be supported if these flightless birds all ate the same thing, and if they ate different things from the flying birds in the region. Unfortunately, neither is true: Cassowaries eat fruit, Emus eat plants and insects, Kiwis eat insects, worms, and spiders, the Kakapo eats plants, and the Takahe eats seeds. And many flighted birds eat one or more of these foods. So then, why are there so many flightless birds in Australia and New Zealand? Well, Cassowaries, Emus, Moas, and Kiwis are all more closely related to one another than to any other group of bird. These birds (along with ostriches and rheas) are all members of a clade of birds called ratites -- and all ratites are flightless. The most likely explanation for ratite flightlessness is that they all inherited the trait from a common ancestor, which had evolved from birds who could fly. The ratites are spread out on modern continents that were once joined in a single landmass called Gondwana about 180 million years ago. So they didn't have to fly to where they are now -- they walked there, and over millions of years continental drift has moved them apart. As for the Kakapo and the Takahe, each bird is closely related to a bird species that can fly, so flightlessness evolved independently in these birds. References Tudge, C. 2000. The Variety of Life. Oxford: Oxford University Press. Press, F. and Siever, R. 1998. Understanding Earth 2nd edition. New York: W. H. Freeman and Co.
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