Publications Archive

Brown skuas (Catharacta skua lonnbergi) on rangatira (south east) and mangere islands in the chatham islands group were studied over a period of 14 years (1978/79 to 1992/93 breeding seasons) to determine factors promoting cooperative breeding in this population. The size and composition of the breeding population and overall breeding success were remarkably stable. No significant differences in breeding success, density of territories or periods of individual occupation in different places on these islands were demonstrated that would demarcate optimal and marginal breeding habitat. Neither could it be demonstrated that the islands were saturated by breeding birds as required for a habitat-forced origin of cooperative breeding.

The migration pattern of Cattle Egrets in 1990 and 1991 and its relation to meteorology are presented to extend initial results covering 1987-1989 (Maddock & Bridgman 1992). Cattle Egrets migrated to Victoria and Tasmania in waves during March and April in northerly air flow (western side of a high pressure system) in a series of stages, with periods of rest in between. Major staging points seemed to be Windsor (NSW), Nowra (NSW), and Baimsdale (Vic). Return migrations (October and November) appeared faster, with fewer and shorter rest stops, and were in southerly airflow. Staging points were Werribee (Vic), Nowra (NSW), and Wyong (NSW). Migrations to and from New Zealand were much more limited than in previous years due to adverse weather conditions, especially winds.

Between 1988 and 1992, we conducted the first comprehensive survey of the number and breeding distribution of the New Zealand Dotterel (Charadrius obscurus) on Stewart Island. The population forms three post- breeding flocks, two of them on Stewart Island; band sightings have confirmed an earlier suggestion that the flock at Awarua Bay, Southland, is also composed of birds from the island. The population is widely spread over difficult terrain during the breeding season; autumn counts of the flocks provide the only practical means of assessing population size. Comparisons with earlier counts show that the population has declined to about one-fifth of its former size in the past 37 years The population is critically endangered because the decline continues and only 60-65 dotterels remain. Average annual mortality of banded adults between 1990 and 1992 was 23%. The major reason for the decline is believed to be predation by feral cats. Band sightings suggest that, apart from Southland, most or all of the recent NZ Dotterel records from the South Island coast (including Farewell Spit) are of juveniles wandering from Stewart Island.

A survey of birds in six Northland forests in 1979 was repeated in 1993, primarily to test whether numbers of New Zealand Pigeon had changed significantly. Counts of Eastern Rosella, Grey Warbler, Fantail and Tui had changed little. Counts of New Zealand Pigeon and Silvereye were significantly lower in 1993 and those of New Zealand Pigeon are thought to reflect long- term changes in abundance. Kaka and Kokako were each recorded in only one forest in 1993 compared with four and three forests respectively in the first survey. Pied Tit and Myna had significantly higher counts in 1993 than in 1979.

In 1990-91, a previously unknown population of the Polynesian Ground Dove was discovered on Rangiroa Atoll in the Tuamotu Is, eastern Polynesia. This apparently isolated population was estimated at only 12-20 birds.

In October-November 1990, Chatham Island Pigeons (Hemiphaga novaeseelandiae chathamensis) in the Tuku a tamatea and Awatotara Valleys, Chatham Island, preferred plants characteristic of mixed broadleaf forest over plants typical of tarahinau forest. Mixed broadleaf forest is confined to gullies and valleys in the region. Browsing by cattle, sheep, pigs and possums is rapidly degenerating these forest remnants. Conservation of Chatham Island Pigeon depends on the protection of these remnants.

The Black-toed Petrel of Latham, on which Gmelin founded his Procellaria melanopus, has not previously been satisfactorily identified. For many years earlier this century, melanopus Gmelin was widely used as the name for the Providence Petrel Pterodroma solandri. On the basis of available evidence it is reasonable to conclude that Latham’s Black-toed Petrel was in fact a specimen of the Mottled Petrel Pterodroma inexpectata, taken in the course of Cook’s third voyage at sea off the north-west coast of North America, probably in the Gulf of Alaska in May 1778.

Aquatic invertebrates were extracted and identified from seven Blue Duck faeces collected from the Tongariro River in December 1990. A total of 927 aquatic invertebrates representing 37 taxa was identified. Over all samples, 45% of the aquatic invertebrates extracted were Chironornidae (samples ranging from 19-76%), 28% Trichoptera (ranging 11-49%), and 16% Ephemeroptera (ranging 2-42%). The dominant chironomid was Eukiefferiella sp., although Cricotopus spp. were also relatively abundant in some samples. Cased caddisflies were the main Trichoptera in all samples, but no one taxon was consistently dominant. Plecoptera comprised 0-20% of invertebrates in the faeces. In most samples collected below Tree Trunk Gorge, chironomids comprised ~61% of individuals recorded in the faeces, whereas above the gorge they comprised ~40% in any sample. Overall, the diet of Blue Duck on the Tongariro River in December 1990 was variable in terms of the proportions of species and the number of invertebrates that were consumed. This has also been shown in studies of Blue Duck diet on other rivers.

Preserved material from two Kakapo (Strigops habroptilus), two Kea (Nestor notabilis) and two Kaka (Nestor meridionalis) was dissected. A fledgling Kakapo had short, stout mandibles, a wide, thick tongue and a thick pharyngeal pad. The lower mandible closed against both the rostra1 end of the hard palate and the underside of the free end of the tongue. The crop was well defined. In the fledgling and in the headless body of an adult Kakapo a fusiform proventriculus was followed immediately by an approximately spherical, uniformly muscular gizzard. There were five main intestinal loops and no evidence of a vitelline diverticulum or of caeca. In Kea and Kaka the upper mandible was longer, the tongue (especially in Kaka) was narrower and fimbriated, and the crop was similar to that of the Kakapo. The mandibles, tongue and palate of the Kakapo appear to be particularly well adapted for the grinding of fibrous plant tissues to extract soft portions and juices.