NEW ZEALAND- WHERE BIRDS ONCE RULED
Monsters We Met #3, deals mostly with New Zealand and how the Maoris impacted the New Zealand archipelago some 700-1000 years ago. It is implied that these Polynesians brought dogs, Polynesian rats (kiore) as well as several tropical plants with them. I had a look at what I could find in the line of peer reviewed articles that would support these claims.
But firstly, how did New Zealand look like 1000 years ago and what animals inhabited these islands? The islands were mostly covered by forests up to the tree-line and tussock in the sub-alpine areas (Holdaway 1989; Wikipedia contributors. Biodiversity of New Zealand). There were no mammals apart from two species of bats, one endemic, that exploited a large variety of food, from foraging on the ground for insects to eating fruit and nectar (Holdaway 1989). The bulk of New Zealand vertebrates were however birds with a few reptiles (only skinks, geckos and tuataras) and frogs making up the rest (Holdaway 1989; Wikipedia contributors. Biodiversity of New Zealand). There were over a 1000 species of snails and a rich variety of insects, some large and flightless as the weta (Holdaway 1989). The birds ruled though, and unlike popular belief there were predators; not mammalian but avian (Holdaway 1989). The Haast’s eagle was one of the largest raptors ever and had a wingspan of up to three meters and capable of taking down even the largest of the moas (Wikipedia contributors. Haast's Eagle). Holdaway (1989) suggests that the presence of predators such as the Haast’s eagle was enough selective pressure to give rise to some birds becoming nocturnal (e.g. kiwi).
New Zealand was one of the last landmasses to have been populated by man, but as with every other landmass a wave of extinctions followed. Several articles support the idea that prehistoric Polynesians introduced not only dogs but also the kiore to New Zealand by about 1300 AD (Holdaway 1989; Holdaway 1999; Duncan and Blackburn 2004). The debate here (yes, there is an academic debate here too!) seems to be what had the biggest impact on New Zealand’s avian diversity; mammalian introductions (Blackburn et al. 2004) or a combination of factors (Didham et al. 2005).
Holdaway (1989) describes the demise to have possibly happened in three pulses. The first pulse coincided with the arrival of man that brought with him two further predators, namely dogs and the Polynesian rat. The birds most susceptible to the kiore were ground or burrow nesting birds, with eggs ≥ 60mm, regardless if these birds were flightless or not (Holdaway 1989; Holdaway 1999; Duncan and Blackburn 2004). These birds simply had no defence against this nocturnal predator that would eat their eggs and had the advantage of rearing several litters per season (Holdaway 1989). During the second pulse many larger-bodied birds were probably driven into extinction through the combination of hunting and habitat loss (Holdaway 1989). This not only included all 11 species of moas, but also the Haast’s eagle, whose prey had been depleted. The third pulse coincided with the arrival of European settlers that introduced more predators, namely two further rat species, cats, possums and mustelids, as well as herbivores that soon altered the habitat (Holdaway 1989).
Duncan and Blackburn (2004) have narrowed it down to two pulses. The prehistoric extinctions, where they found that large-bodied birds and ground or burrow nesting birds were most vulnerable to extinction due to hunting by humans and predation by the kiore respectively and the historic extinction, where endemic birds with an intermediate body mass (32-320g) as well as being flightless made them particularly vulnerable to the newly introduced predators. The level of endemism seemed to have played a significant role in the proneness to extinction at all times (Duncan and Blackburn 2004).
Duncan et al. (2002) evaluated fossil avifauna data from Marsfells Beach, South Island and found that the Maoris there specifically favoured large-bodied birds because of their size and not because they were flightless. They also found that different birds “were differentially susceptible to extinction” (p.517). Those birds with a slow growth and reproductive rate were more susceptible to extinction, as they could not reproduce fast enough to keep up with the rate that they were being hunted (Holdaway 1989; Duncan et al. 2002) But hunting was clearly not the only reason birds became extinct, as birds that were clearly not favoured by Maori hunters at Marsfell Beach, also became extinct according to Duncan et al. (2002). This was probably due to habitat destruction as large parts of lowland forests were cleared for agriculture (McGlone and Basher 1995).
There seems to be little debate about the impact humans have had in New Zealand since their arrival between 700-1000 years ago. A recent debate seems rather petty as it is about the positive correlation of the number of introduced predatory mammal species since European settlement and bird extinctions (Blackburn et al. 2004) and a multi-factoral cause for bird extinctions since European settlement ( Didham et al. 2005; Wikipedia contributors. List of extinct New Zealand animals). The most birds however (at least 34) became extinct before European settlement in New Zealand (Duncan et al. 2002) and a further 19 became extinct after European settlement (Wikipedia contributors. List of extinct New Zealand animals). Towns and Daugherty (1994) also concluded that the major cause of herpetofauna extinctions since the arrival of humans certainly is the introduction of predatory mammals. Although they do not disregard hunting and habitat loss as secondary causes, they came to the above conclusion because species diversities and densities are much higher on rat-free islands, more nocturnal species of herpetofauna have become extinct (nocturnal species are more vulnerable to nocturnal predators) and on islands where rats have been eradicated, the lizard populations have made a remarkable recovery. Blackburn et al. (2004) came to the same conclusion that extant native birds have managed to survive on islands that have stayed rat free, yet intact natural forest vegetation that harbours introduced mammals is almost devoid of native birds. All factors have certainly played their role. Both New Zealand’s main islands have been greatly transformed and hardly harbour any native fauna. Only the most resilient have survived… and in New Zealand’s case the climate does not seem to have played a great role (Holdaway 1989).
Yet again I am dumbstruck by the utter destruction our human race has brought upon a land. Clearly this was not intentional, but the results are the never the less the same. 40% of New Zealand’s fauna has been eradicated within 1000 years of human occupation and more worrying even is that 41% of the extant fauna only barely survives on some rat-free offshore islands (Towns and Daugherty 1994). Have we indeed become the monsters, as "Monsters we met #3" suggested?
Blackburn TM, Cassey P, Duncan RP, Evans KL and Gaston KJ. 2004. Avian Extinction and Mammalian Introductions on Oceanic Islands. Science 305:1955
Blackburn TM, Cassey P, Duncan RP, Evans KL and Gaston KJ. 2005. Technical Comment: Response to Comment on “Avian Extinction and Mammalian Introduction on Oceanic Islands”. Science 307:1412b.
Didham RK, Ewers RM and Gemmell NJ. 2005. Technical Comment: Comment on “Avian Extinction and Mammalian Introductions on Oceanic Islands”. Science 307:1412a.
Duncan RP, Blackburn TM and Worthy TH. 2002. Prehistoric bird extinctions and human hunting. Proceedings of the Royal Society of London, B 269:517-521.
Duncan RP and Blackburn TM. 2004. Extinction and endemism in the New Zealand avifauna. Global Ecology and Biogeography 13:509-517.
Holdaway RN. 1989. New Zealand’s pre-human avifauna and its vulnerability. New Zealand Journal of Ecology 12(supplement): 11-25.
Holdaway RN. 1999. Introduced predators and avifaunal extinction in New Zealand. In: McPhee RD, editor. Extinctions in Near Time. New York: Kluwer Academic/Plenum. p 189-238.
McGlone MS and Basher LR. 1995. The deforestation of the upper Awatere catchment, Inland Kaikoura Range, Marlborough, South Island, New Zealand. New Zealand Journal of Ecology 19;53-66.
Towns DR and Daugherty CH. 1994. Patterns of range contractions and extinctions in the New Zealand herpetofauna following human colonization. New Zealand Journal of Zoology 21:325-339.
Wikipedia contributors. Biodiversity of New Zealand [Internet]. Wikipedia, The Free Encyclopedia; 2006 Jul 27, 21:05 UTC [cited 2006 Aug 6]. Available from: http://en.wikipedia.org/w/index.php?title=Biodiversity_of_New_Zealand&oldid=66231303.
Wikipedia contributors. Haast's Eagle [Internet]. Wikipedia, The Free Encyclopedia; 2006 Aug 1, 11:39 UTC [cited 2006 Aug 6]. Available from: http://en.wikipedia.org/w/index.php?title=Haast%27s_Eagle&oldid=67023162.
Wikipedia contributors. List of extinct New Zealand animals [Internet]. Wikipedia, The Free Encyclopedia; 2006 Jul 31, 05:42 UTC [cited 2006 Aug 6]. Available from: http://en.wikipedia.org/w/index.php?title=List_of_extinct_New_Zealand_animals&oldid=66808010.
Image credit: http://www.nzbirds.com/birds/haasteagle.html
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University of the Western Cape
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