Double Invasions

Forest and Bird, Issue 295, 1 February 2000, Page 34

Double Invasions

in which one member of the pair is either larger, or less able to fly, or darker, or a combination of these characteristics. These pairs of species represent double invasions of New Zealand by the same ancestral stock. The descendants of the earlier invasions evolved into distinct species which, in the absence of snakes and mammalian predators, sometimes became larger and less adept at flying. The second invasion was often so recent that the descendants are little different from their relatives in Australia. Double invasion has been an important mechanism for generating new species among New Zealand birds. It is speciation by the separation of populations in time. In continents it is more usual for speciation to be by the separation of populations in space (geographically). The pairs of species most likely to represent double invasions (with the result of the earlier invasion given first) are: e weka — banded rail e takahe (two species) — pukeko e black stilt — pied stilt e Antipodes Island parakeet — red-crowned parakeet e New Zealand robin — New Zealand tomtit Other pairs that perhaps stem from double invasions (result of earlier invasion first): e moas — kiwis e Dieffenbach’s rail — banded rail e Chatham Island rail — banded rail e Hodgen’s rail — black-tailed native-hen e giant coots (two species) — Eurasian coot e giant Chatham Island snipe — Chatham Island snipe e New Zealand dotterel — banded dotterel e kakapo — kaka and kea e laughing owl — morepork e Chatham Island warbler — grey warbler f\ mong New Zealand terrestrial birds there are pairs of closely related species