Publications Archive

We studied North Island robins over 7 breeding seasons following their reintroduction to Tiritiri Matangi Island. All robins bred in their first year if a mate was available. They usually retained pair bonds for life but some females switched mates within or between breeding seasons. There were 2 instances of sequential polyandry, where a female laid a clutch with a new male while her previous mate was rearing her fledglings. The 1st clutches were usually laid in early September and the last clutches in late December or early January. Mean clutch size was 2.3 eggs, and clutches were largest in the middle of the breeding season. Females reared a maximum of 3 broods per year, and a maximum of six fledglings. Females that survived the breeding season fledged an average of 2.48 young, and 51% of clutches found before hatching fledged at least one young. Juveniles were fed for 4- 7 weeks after fledging, and stayed in the natal territory for 7-10 weeks. Dispersing juveniles were often chased when entering other territories, but there were 4 instances of juveniles being fed by unrelated lone males. The juvenile survival rate declined as the population grew. Permanent territories were restricted to patches with a canopy of at least 6 m, totalling about 13.4 ha, and the breeding population levelled off at 65 in the 5th year. The decline in juvenile survival was similar for males and females, suggesting that both sexes needed to compete for territories even though there were always males without mates because of an initial bias in sex ratio. Males had delayed plumage maturation whereby they appeared similar to females or juveniles until after their first breeding season. We suggest this could be advantageous for territory acquisition because male territory holders cannot be preferentially aggressive toward juvenile males.

This paper describes the activity of garden, bush and riverine birds in the Western Hutt hills, 1981-92. The area is 15 km north of Wellington, 7 km north of the Hutt River estuary, and 15 km south of Pauatahanui Inlet, Porirua Harbour, on the southwest coast of the North Island. Observation is based on 35 years’ residence and >12 500 10-min counts conducted between 1981 and 1992. Species first seen each day are distinguished from those first heard. Whenever possible the birds’ food was recorded. The western hills have fewer native passerines than similar habitat on the eastern hills. Several species increased or decreased during the study. Some apparent decline was attributed to the author’s hearing loss. Wind reduced bird detection. Nectar of New Zealand flax (Phormium spp.) was eaten by silvereyes (Zosterops lateralis), tui (Prosthemadera novaeseelandiae) and starlings (Sturnus vulgaris) at different times. In the study area there were about 0.9 cats (Felis catus) per household, a potential predator on birds.

We investigated the use of call count surveys to monitor weka numbers for management purposes. A Generalised Linear Model based on data from 11 1 nights of listening for weka at Rakauroa (North Island, New Zealand) showed that the number of calls recorded was influenced by listening site and month, but not by wind direction, wind strength, cloud cover, phase of the moon, rainfall or temperature. Mean number of calls heard was highest between December and March, with a peak in January. More birds were heard from certain listening sites. Although there was no correlation between any of the environmental variables and weka calling, wind, and rain may have reduced the audibility of weka in other studies. The estimated probability of detecting weka was 60-80% (mean = 728). At least 3 nights at each listening station were necessary to improve the census accuracy. Call counts of weka at Rakauroa between 1993 and 1997 showed a decline in the number of weka.

The total population of North Island weka (Gallirallus australis greyi) is about 4150 adults spread over five islands, one North Island population, and a number of captive birds in aviaries and mainland island programmes. Between 77% and 84% of the adult weka population are on Kawau Island. Density changes in the Mansion House Historic Reserve, and anecdotal records suggest that adult weka populations on Kawau Island has fluctuated between c.2100 and c.5000 during 1992-1999. The largest declines occurred within 12 months of the 1990-91 and 1997-98 droughts.