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View Full Version : New Zealand's pre-human avifauna and its vulnerability



morfrain_encilgar
Thursday, June 2nd, 2005, 08:52 PM
Here is the text and abstract of a study of birds and their habitat in New Zealand before humans arrived.

Most of the extinctions were before humans arrived and studies of the role that moas had in the environment of New Zealand have been based on assumptions. "Moas (Aves: Dinornithidae, Anomalopterygidae) were indeed impressive members of the diverse avifauna in prehuman New Zealand, but their effects on vegetation in the Late Holocene cannot be discussed without considering the palaeo-ecosystem as a whole. Other herbivores were present and the moas (themselves a much more diverse ecological group than is usually appreciated) were subject to the same pressures of predation and dispersion of food resources as other animals. Several of the papers in this volume treat the group as 'the moa' and assign 'it' mammal-like characteristics. Others argue on very tenuous premises for, say, flocking behaviour, and then attempt to assess population size and grazing pressure."

The moas naturaly were preyed on mostly as chicks by indigenous goshawks (though there was also a large eagle in New Zealand that ate adult moa), and after rodents arrived, rats outcompeted the juvenile moas for food (such as insexts). There is a paralell with the tuatara which faces predation from rats in the juvenile stage.

For smaller birds, the arrival of rodents caused extinctions too. ""Whereas the avian predators were double-brooded at most, kiore could raise several litters in a season and some of those young could themselves breed in the same year. The principal characteristic of the prey fauna was not high absolute numbers but high diversity, as in a tropical forest today. The original equilibrium between predators and prey would have been upset easily and catastrophically by the arrival of a new, nocturnal predator with a high reproductive potential."

The extinctions in New Zealand are compared to those of the megaherbivores in North America. "However, the New Zealand event was unlike that in North America because there were no 'pivotal megaherbivores', whose removal could result in environmental changes sufficient to precipitate the extinction of other species (Owen-Smith, 1987). In New Zealand, humans could directly affect the environment on a large scale, in a short time".

Some of the birds which are discussed are the moas, and Haast's eagle. The decline of bird species that are known to survive, or else became extinct recently, is blamed on Europeans.

"New Zealand's pre-human avifauna and its vulnerabilitym"

"Summary: In the past 1000 years New Zealand has experienced a major 'extinction event', losing 40-50% of the avifauna, at least 50% of the frog fauna, and unknown proportions of the lizard and invertebrate faunas. During this period, bird species became extinct at different times and rates depending on the particular aspects of their ecology and life history which made them vulnerable to habitat loss, hunting, predation, and competition for food resources. Three groups of species with different levels of vulnerability are recognised within this event:

Group I, 1000-1200 AD - species susceptible to initial impact of hunting by Polynesians and dogs, and predation and competition for food after an explosive irruption of kiore (Rattus exulans);

Group II, 1200-1780 AD - species more resilient but gradually reduced by Polynesian hunting and continuous clearance and fragmentation of habitat;

Group III, 1780-present - species susceptible to hunting with European weapons and predation by Rattus norvegicus, R. rattus, mustelids, cats, and to competition by mammalian herbivores, and destruction of wet forest and wetland habitat.

Climatic change is seen as a negligible influence relative to these major intrusions. Discussions of the pre-human avifauna have so far concentrated almost exclusively on moas (Aves: Dinornithidae, Anomalopterygidae), partly because information on the other extinct species is sparse. The ecology of 12 species in the pre-human avifauna is inferred from their anatomy, relationships to extant species, sub-fossil evidence of diets, and analogy with
related forms elsewhere."