Publications Archive

North Island robins are sexually dimorphic, males having darker plumage on their back and upper breast. However, males show delayed plumage maturation, and do not acquire the characteristic male plumage until after their first breeding season, 12-16 months after fledging. Therefore, sexing based on plumage alone will overestimate the proportion of females, and this may result in highly skewed sex ratios for translocations. Using measurements from robins of known sex on Tiritiri Matangi Island, I found tarsus length to be a useful indicator of sex. Of 82 robins measured, 80% of birds with tarsus length greater than 35.6 mm were male and 77% of other birds were female. If tarsus length is used in combination with plumage, it should allow sex ratios to be estimated reasonably accurately and without bias. However, additional data including wing chord measurements suggest that wing chord is superior to tarsus length for determining sex.

Reports of dispersal by juvenile weka (Gallirallus australis greyi) on the North Island are rare. Estimates of the distance dispersed and the rate of survival of dispersers are important factors to be considered for weka conservation. I captured 20 young weka during a 2-year study and attached radio transmitters to 4 of them. In addition, I was able to measure the distance travelled by 3 banded weka that were either recaptured or seen again, and 1 weka that was recovered dead. Newly independent weka used a part of their parental home range at first, then moved up to 3.5 km. Two-stage dispersal, where young weka leave their parents but remain close by and move away later, has been reported on offshore islands: my results are consistent with that type of dispersal. More research is needed on weka dispersal because it is likely to be linked to factors important for their conservation and management.

A species of small procellariid known locally as titi, probably the black-winged petrel (Pterodroma nigripennis), nested into the historic period in burrows in the volcanic soil of the uplands of Mangaia in the southern Cook Group. The demise of this titi as a breeding bird on Mangaia was probably caused by a combination of the detrimental effects of human harvesting and various introduced mammalian predators which were present on Mangaia after the arrival of missionaries in the early nineteenth century.

The Chatham Island pigeon or parea (Hemiphaga chathamensis) is an endangered species of pigeon endemic to the Chatham Islands. Effective conservation management of the Chatham Island pigeon required an understanding of its ecology and identification of the causes of decline. We studied the pigeon in their last remaining stronghold; the south-west of Chatham Island, New Zealand, between July 1991 and December 1994. We describe the nesting behav- iour, nesting success, and the dispersal, survival, and recruitment of juveniles. The study was confounded by the lack of information on predator numbers or outcomes of pigeon nests from before the start of predator control activities within and adjacent to our study area. Despite a previously reported decline in pigeon numbers up until the early 1990s, during this study there was a 3-fold population increase, and only a low level of predation by possums and rats. Other than predation, no factor which might previously have limited the pigeon population was identified. We assume that the trapping and poisoning of pest-mammals since 1989, has been sufficient to allow the population of Chatham Island pigeon to recover.

The yellow-eyed penguin (Megadyptes antipodes) on the South Island of New Zealand was believed to have suffered a population decline that continued into the 1980s. Unpublished census results from L. Richdale (1930s-1950s) and S. Sharpe (1950s-1960s) for Otago Peninsula show that there were only 44 nests in 1940, but the number increascd in the 1940s-1960s. Numbers peaked at 276 nests in the mid-1980s. Subsequent decreases and a crash to 79 nests in 1990 led to concerns for the viability of the population, but years of good survival and breeding allowed a recovery. The fluctuations were probably drivcn by interplays of human impacts and environmental variation. Reservation of breeding areas, revegetation, and predator control have reduced the deleterious human impacts and given the species a chance to increase numbers and withstand adverse fluctuations in the cnvironment.