Publications Archive

During 1994, participants in the Beach Patrol Scheme patrolled 3253 km of the New Zealand coastline. 5477 dead seabirds of 55 species, plus 121 individuals of 25 non- seabird species were found. Unusual finds were the first New Zealand record of a Newell’s Shearwater (Puffinus newelli), one Soft-plumaged Petrel (Pterodroma mollis) and one Eastern Little Tern (Sterna albifrons sinensis). Large numbers of Kerguelen Petrels (Lugensa brevirostris), Flesh-footed Shearwaters (Puffinus carneipes) and Buller’s Mollymawks (Diomedea bulleri) were beach-cast in 1994. Fisheries-related mortality was identified for some seabirds found on beach patrols.

The Saddleback (Philesturnus carunculatus) is now confined to New Zealand offshore islands free of the introduced carnivorous mammals, i.e. rats, feral cats and mustelids, which are assumed to have exterminated the species on the mainland during the last century. The North Island Saddleback (Philesturnus carunculatus rufusater) coexists with the Polynesian rat (Rattus exulans) while the South Island Saddleback (P c. carunculatus) thrives only on rat-free islands. An experimental transfer to Kapiti island, where Norway (R. norvegicus) and Polynesian rats occur, provided an opportunity to test the hypothesis that North Island Saddlebacks could coexist with both rat species. I compared the survival of Saddlebacks on Kapiti Island wlth that on Cuvier and Little Barrier Islands where the only rodent is R. exulans. On Kapiti Island, Saddlebacks suffered high mortality, and despite high productivity, there was insufficient recruitment of young to balance losses of adults. Significantly more nests sited less than one metre above the ground were preyed on by rats on Kapiti Island than on Cuvier and Little Barrier Islands. Saddlebacks on Kapiti Island which roosted in high or secure cavities survived longer than those birds which roosted in low or vulnerable places. These observations are consistent with the ground-foraging and predatory behaviour of R. norvegicus. On Kapiti Island, 21 rat-killed birds were found at nests and roosts, whereas no rat-killed birds were found at nests and roosts on Cuvier and Little Barrier Islands, although the contents of some nests were preyed on by R. exulans. On Kapiti Island, R. norvegicus faeces were found with the remains of several dead birds, providing direct evidence that this rat was the predator. The poor survival and recruitment of Saddlebacks on Kapiti Island, coupled with observations of rat-killed birds and plundered nests near the ground, suggest that Saddlebacks are unable to coexist with both rat species, and that R. norvegicus is probably an important predator. The cavity nesting and roosting habits of the Saddleback make this species especially vulnerable to mammalian predators.

In October-November 1992 the island of Mangaia, Cook Islands, was surveyed for Tanga’eo (Halcyon tuta ruficollaris). The Tanga’eo was found to be primarily a forest bird, preferring continuous forest canopy. Its abundance was influenced by forest type, extent, and degree of habitat modification. A number of potential threats to the survival of Tanga’eo were identified including habitat loss and disturbance by Common Mynas (Acridotheres tristis). A brief survey of rodents was carried out. Although the Tanga’eo population was estimated to have been between 250 and 450 birds, low numbers of birds in apparently suitable forest in the southwest of Mangaia indicate that further research is needed to determine population trends and conservation requirements.

The breeding behaviour of Tanga’eo or Mangaia Kingfisher (Halcyon tutu ruficollaris) on the island of Mangaia in the Cook Islands was investigated in 1992. Calls and breeding behaviour are described from a study of pairs and trios. At least six calls were distinguished. Clutch size appeared to be two eggs for pairs and three eggs for trios. Incubation time was between 21 and 23 days, while the fledging period was estimated at approximately 26 days. Both birds of a pair and all members of a trio excavated nest holes, incubated, brooded and fed the chicks. In trios with two males, both males courtship fed and copulated with the female, suggesting a polyandrous relationship. The breeding behaviour and relationship of trios, and the effects of Mynas on breeding success warrant further investigation.

We present new distributional data from the eastern South Pacific Ocean for the White-headed Petrel (Pterodroma lessonii), Kerguelen Petrel (P. brevirostris), and birds showing characters of the endangered Magenta Petrel (P. magentae). Extrapolation of density for White-headed Petrels suggests a pelagic population of 18,770 birds for the 10( x 5( block of subtropical surface waters between 27-37(S and 80-85(W (August 1995). Two Kerguelen Petrels were noted off Chile at around 40(30’S 74(50’W (August 1995). Three sightings of apparent Magenta Petrels between 28(44’S 72(40’W (March 1992) and 36(24’S 78(02’W (August 1995) are reported to alert observers to the potential occurrence of this species off South America.

Morphological comparison of the extinct Huia (Heteralocha acutirostris) with its closest known relatives suggests that the pronounced sexual bill dimorphism of the former evolved through selection on female, rather than male bill form. Because sexual selection acts predominantly on males, it cannot readily explain such dimorphism in a non-polyandrous species. Greater female divergence in foraging-related anatomy in a species in which males are the larger (and therefore presumably socially dominant) sex is, however, consistent with the hypothesis that sexual dimorphism can be an adaptation to reduce intersexual competition for food. Determining which sex changed most is a more rigorous means of establishing the evolutionary significance of sexually dimorphic traits than interpretation of current function.