Observations of birds were made while working on fishing trawlers intermittently for a total of almost a year in New Zealand subantarctic waters. Large numbers of several species of albatrosses and petrels are attracted to trawlers to scavenge and their numbers vary throughout the year. Species not attracted are seen less commonly. Scavenging behaviour around trawlers is discussed. There seems to have been an increase in scavenging by certain species in the last 30 years.
There are major sexual differences in the calls of thin-billed prion Pachyptila belcheri. This allowed birds to be sexed initially by calls, and then by their measurements. Males were on average larger than females for six out of eight morphometric characters, with the greatest difference being in the bill. We then investigated the possibility of sexing birds on the basis of external measurements: a discriminant function analysis based on the eight measurements allowed correct classification of 84.4% of the 281 birds. In 89% of breeding pairs, males had greater bill depth than their partner. A stepwise discriminant analysis revealed that bill depth, head length and body weight were the three most discriminant variables. The combinations of two measurements (bill depth and body weight, or bill depth and total head length) allowed correct classification of 84.3 and 83% of the birds respectively, whilst a classification solely based on bill depth gave a 83.2% correct classification. The degree of sexual dimorphism in this species is similar to that found in other tubenoses.
Kaka (Nestor meridionalis) less than one year old can be distinguished from older birds by a pale ring of skin around the eye (periophalmic ring). In birds less than five months old this has a yellow tinge, as does the cere, gape and the soles of the feet. A further distinguishing feature of kaka between three and six months of age are protruding rachides (feather quills) on the tips of the tail feathers. On Kapiti and Little Barrier Islands, most kaka nestlings fledge in February and receive food from their parents until June or July. Fledglings can often be detected during this period by their conspicuous and frequent food-begging behaviour. Juvenile characteristics in the kaka persist for a much shorter period than in the kea (N. notabilis), its sole extant congener. The loss of juvenile characteristics prior to sexual maturity suggests that juvenile kaka becomes socially independent of adults earlier than kea, presumably because of more readily obtainable food sources in their environment.
During a census in gardens in Hamilton, 71.8% of the 4428 birds observed belonged to introduced species. A total of 15 species were observed. Bird species richness was positively correlated with native plant biomass and, more strongly, with total plant biomass. More birds were present in gardens with more native plants. Among the most common species, the abundance of the house sparrow (Passer domesticus) decreased with increasing percentage of native plants, the silvereye (Zosterops lateralis) increased, while blackbirds (Turdus merula) and starlings (Sturnus vulgaris) showed no significant change. This was typical for other introduced bird species. Most other birds, including the fantail (Rhipidura fuliginosa) and the grey warbler (Gerygone igata), were most abundant in gardens with higher native plant biomass. Notable was the absence of the tui (Prosthemadera novaeseelandiae) from all censused areas in Hamilton at the time of observation. No significant variation between morning and evening samples was noted.
During a visit to North Brother Island in Cook Strait from 11 October to 6 November 1990, we estimated by quadrat sampling that the 4 ha island supported 1000 pairs of fairy prions, 600 pairs of common diving petrels, and 225 adult tuatara. Most diving petrels nested below Coprosma scrub, and a few eggs were laid on the surface under dense shrubs. Many prion burrows were in more open vegetation. Burrows of both species were simple and were not shared with tuatara. Some evidence of tuatara preying on unattended eggs was found, but there was no evidence that the endemic Sphenodon guntheri, which is smaller than S. punctatus, fed on adults of either species. Many diving petrels, prions, fluttering shearwaters and red-billed gulls fed in tide rips close to the island. The position of each species in feeding assemblages was related to their dive depths. diving petrels in areas of strong currents submerged for only a few seconds at a time, but in areas of calm water dive durations averaged 29 seconds.