Tasmanian Native Hen Research Articles

Damage to pastures by the Tasmanian native hen, Tribonyx mortierii

Exclosure trials over 2+ years showed that grazing by native hens and rabbits on an established pasture caused a sharp check to spring growth and a subsequent decline in height. Counts of faeces showed that although grazing by native hens was fairly even throughout the year, a considerable increase in grazing by rabbits coincided, two years running, with this check of growth and decline in pasture height. It is concluded that rabbits were doing more damage than native hens.

Damage to oat crops by the Tasmanian native hen, Tribonyx mortierii

Damage by native hens, Tribonyx mortierii, grazing on young cereals constitutes their chief importance to agriculture. Native hens were responsible for a reduction of weight of yield, at 6-8 weeks after sowing, of 24-36% on the immediate edge of the one margin of a paddock that bordered water. For the entire paddock, the overall reduction of weight attributable to native hens was 8%. The grazing pressure of native hens was greater than that of rabbits on the edge nearest water, but the situation was reversed over the rest of the paddock. Even though the rabbit population was low because of earlier and more recent poisonings, damage attributable to rabbits was equal to damage by native hens. Clearance of the rough vegetation around the small paddocks near water, where damage by native hens occurs, is the best permanent remedy. When this is impracticable, local poisoning may be necessary. Widespread control campaigns are unnecessary and indeed are undesirable, as this flightless bird is conked to Tasmania and could become extinct.

THE BIRDS OF TASMANIA: ECOLOGY AND EVOLUTION

SUMMARYTasmania, about the size of Ireland, separated from the Australian mainland by 140 miles of sea, and isolated for about the last 12,000 years, has 104 species of native breeding land‐birds, with the addition of ten introduced species. The environment is described; in particular the vegetation is classified into nine natural types and three produced by European man; and the distribution of the bird species among these is defined and discussed. The other vertebrates are briefly considered. No extinction is definitely known to have taken place as a result of European settlement except of the Tasmanian Emu (and of course Tasmanian Man).An attempt is made to reconstruct the Late Pleistocene history of Tasmania and its vegetation, with special reference to the Last Glaciation, when the island would have been joined to the mainland.When the avifauna is divided into categories, water‐birds, raptors, etc., it is found to have much the same proportional composition as the Australian mainland avifaunas with which it is compared, though it consists of many fewer species.The vegetation types of the colder and wetter areas of Tasmania house far fewer species of birds than the drier and warmer habitats. The 104 breeding species include 14 endemics, which are considered in detail, and 27 endemic subspecies. As shown by comparison with other islands, the total proportionate endemism is extraordinarily high for a recent continental island (though it is actually lower than that in the remote ecological island formed by the sclerophyll of southwestern Western Australia). A contributory cause may be that Tasmania is not regularly visited by land‐birds from the continent (though at least one‐fifth of the Tasmanian species are partial or total migrants in winter). The most noteworthy endemics are two monotypic genera,LathamusandAcanthornis, and the Native HenTribonyx mortierii, which has become flightless apparently in the face of a formidable array of local predators.Considerations of climate and habitat suggest that at least half the avifauna, including 19 of the endemic subspecies and six of the members of superspecies, arrived in Tasmania some time after the amelioration of the Last Glaciation began, some 18,000 years ago. Geographical considerations suggest that four of those six members of superspecies existed in their present form when the land‐bridge to the mainland was cut, 12,000 years ago. Certain habitats, widespread over southeastern Australia during the glaciation, are now virtually confined to Tasmania where they form the stronghold of certain species, such as the Pink RobinPetroica rodinogaster, which occur only as relicts on the mainland. The endemic Scrub TitAcanthornis magnusis practically confined to such habitats, where its ecology suggests it would have been well adapted to glacial conditions.Among the local endemics there is a strong tendency for colouration to be more saturated than on the continent of Australia (Gloger's rule) but there is less consistency in tendency to greater size (Bergmann's rule). A noteworthy proportion of the Tasmanian species have duller plumage than their mainland relatives, usually with an assimilation to female or juvenile plumage—unexpected in an island as big as Tasmania with so considerable an avifauna.