The Ancestry of Birds

Forest and Bird, Issue 295, 1 February 2000, Page 32

The Ancestry of Birds

A new book, New Zealand's Unique Birds by BRIAN GILL includes a popular account of new discoveries about the origins of our birds. These extracts discuss their evolution, and relationships with birds of other regions of the world.

he endemic birds of an area — those originating there and found in the wild nowhere else — are always of special interest. Among New Zealand’s unique birds we find, for example, such species as the world’s largest living rail and largest living parrot. Among the extinct species were the world’s tallest bird, biggest penguin, biggest eagle and biggest owletnightjar. New Zealand is a ‘centre of endemism’ — a region where the relative proportion of

endemic species is high. There are two main reasons. Firstly, New Zealand is an ancient land in the sense that for more than 80 million years it has carried a varied and unique assemblage of plants and animals. This is in contrast to the situation in northern Europe and the British Isles, for example, where the advance of ice sheets during the ice ages periodically displaced many of the animals and plants. Those that returned to Britain and Europe after the last ice age, 15,000 years ago, were widespread Eurasian species. Meanwhile, New Zealand kept an ancient biota, even though at times it was limited to small areas of refuge. Secondly, New Zealand represents a natural experiment on a grand scale. If the mammals of the world had died out along with the dinosaurs 65 million years ago, and if birds had thus come to dominate the terrestrial habitats unchallenged, how would birds have evolved? The development of New Zealand birds in the absence of mammals has given answers to questions like these, and yielded a bird fauna rich in endemic species. (In all we have 120 endemic bird species.)

particular arrangement of the higher groups of birds had been traditional. This arrangement placed kiwis, grebes, tube-nosed seabirds and penguins near the start of the sequence, passerines (perching birds) at the end, and rails, cranes, waders and gulls at about the middle. The arrangement reflected accumulated data on the morphology of birds (including their bones and other structures, internal and external) FE: many decades, up to the 1980s, a

and on their behaviour. Then scientists began looking at biochemical characters (such as the nature of egg-white proteins) to see if these could give objective indications of the relationships of birds. Techniques have also been developed to study the chemical behaviour of strands of DNA, the genetic material itself. These studies of the molecular biology of birds, especially the DNA work, have sometimes supported traditional ideas of which bird groups are most closely related, and other times suggested radically new relationships. Accepting all the results of the DNA studies has led to a very unorthodox rearrangement of the higher bird groups, which many people are following. However, it is most unlikely that biochemistry alone can produce the final word on bird relationships. What molecular biology yields up is just another taxonomic character to be weighed against all others. One of the exciting things about birds is that they are the best-known animal group. It seems that, for the first time, we are getting tantalisingly close to working out the actual evolutionary family-tree ("phylogeny ) of an entire animal group.