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Haast's Eagle

Prior to human settlement, New Zealand was dominated by large avian species without the presence of terrestrial mammals. This top predator, Haast’s Eagle, Harpagornis moorei, is the largest eagle to have ever lived on this planet. Weighing in at 10-15 kg with a 2-3 m wingspan, this bird could tackle now extinct Moa (standing up to 3 m tall and numbering 11 species so far) up to 15 times it’s own weight (Bunce et al., 2005). Although approaching the maximum body mass allowing for powered flight, it killed its prey by piercing and crushing with its huge talons. These talons ‘could pierce and crush bone up to 6mm thick under 50mm of skin and flesh’ (Bunce et al, 2005). Fossil remains of moa have indicated attack was aimed at the pelvic area. When a grip was established, death followed with a ‘single strike by the other foot to the head or neck’ (Bunce et al., 2005).

Bunce et al. (2005) analysed the DNA of Haast’s Eagle and compared it to 16 extant eagles. They discovered that Haast’s eagle could be placed in the clade with a group of small eagles of the genus Hieraaetus. This includes H. Morphnoides, the little eagle, and H. Pennatus, the booted eagle, which both had a wingspan of 1.2 m and weighed approximately 1 kg. ‘Genetic distances suggest a recent common ancestor about 0.7-1.8 million years ago (early to mid Pleistocene)’ (Bunce et al, 2005). Hence it is thought that a small bird-eating Asian/Australian Hieraaetus eagle migrated to New Zealand and increased rapidly in size. Factors that could have induced this size increase may have been: ‘size of potential prey, competition with small harriers and complete lack of terrestrial predatory mammals in New Zealand’ (Bunce et al., 2005). Moa were the largest herbivore on the island and so there was a vacant niche for a large predator. The ancestor of the Haast’s eagle evolved rapidly displaying a dramatic increase in body size, assisted by the lack of competition. Haast’s eagle is a good example of the island rule . Nonetheless extinction soon followed the arrival of humans in the 13th century and the addition of terrestrial mammals such as rodents and cats. Rodents predated upon the eggs and chicks and humans hunted Moa and possibly the eagles themselves. This decline in prey items and surviving chicks induced their ultimate extinction.

References and Resources

  • Bunce, M. et al.. 2005. Ancient DNA provides new insights into the evolutionary history of New Zealand’s giant eagle. PLoS Biology. 3, 44-46.

  • Authored by Emma Kerridge & Chris Rogers

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