Field Research

Study Populations

Red-billed gull study

The red-billed gulls breeding at Kaikoura Peninsula, New Zealand are an ideal subject for population and genetic studies because there is little emigration of breeding adults and virtually all of the offspring of breeding age return to the environs of Kaikoura during the breeding season. The population is the third largest in New Zealand. Annually 2315-9212 pairs nested on the three kilometre headland of the peninsula. Banding of nestlings has continued annually since the 1958 breeding season and to date 71,000 chicks have been banded resulting in a large proportion of the population being of known age. The birds have lived up to 31 years of age. Research on the population began in 1964. In all, seven generations have been studied and a total of 5000 individuals have been individually colour-marked. Currently it is one of the largest avian data-bases in the world. In the data-base there are records of over 45,600 individuals, 182,000 recoveries consisting of dead recoveries, recaptures or resightings of banded individuals and 25,000 records of breeding attempts by known-aged colour-marked adults. Between 1992 and 2004, blood samples were taken from 1,650 family groups.

Between 1983 and 1993 the total population at Kaikoura remained relatively stable at approximately 16,000-19,000 individuals, but after 1993 the population declined and by 2003 numbers had decreased by 51% from that in 1983.

Takahe Study

Takahe are one of the most endangered birds in New Zealand. The sub-fossil record indicates that this endemic rail was once widely distributed throughout New Zealand. In recent times the birds have been restricted to approximately 650 sq km in remote regions of Fiorldland National Park in the southwestern corner of New Zealand. Thought to be extinct for 50 years, the bird was rediscovered in 1948. Following a decline reported by Brian Reid 1972, a major study was initiated to establish the causes of the decline and to formulate management options to rectify the situation. The study commenced in 1972 and continued until 1993. It expanded the breeding and survivorship investigation to three study areas in different parts of the birds’ range. The study examined many aspects of the ecology of the bird to determine the cause of the decline:

  • The impact of stoat predation on adults and offspring
  • A detailed investigation of food requirements of the bird including the nutrient requirements, digestability of plant constituents, and the impact competition for food from introduced red deer for preferred food items.
  • Winter diet and tracking of transmittered birds
  • Seasonal and regional variation of deer diet.
  • Seeding of tussocks and beech trees was monitored for 21 years to investigate the impact of increased food quality during mast seeding years. Seeding of beech trees increase the survival of mice and consequently the abundance of stoats.
  • Changes in the nutrient quality of tussocks from the application of fertilizers and food selection in relation to changes in nutrient content. The application of fertilizers was a management option to increase the quality of food for the bird.

The major cause of the decline of takahe has been competition by red deer for the most nutritious plants. The bird essentially extracts only the soluble components from the basal portion of tussocks and so is dependent on plants with the highest nutrient content. Feeding by deer and takahe on the same tussock plants induced a long-term decline in the biomass of the tussocks by 64% than tussocks that were uneaten by deer. It is estimated that it would take 20 years for the tussocks to recover, even if no further grazing by deer occurred. Tussocks are not adapted to browsing by deer