Burrowing seabirds affect forest regeneration, Rangatira Island, Chatham Islands, New Zealand

The forests of Rangatira Island (218 ha) in the Chatham Islands are a critical breeding site for a number of rare and threatened forest bird species, but are also home to more than three million seabirds, which could significantly affect forest regeneration processes. We surveyed the forests of Rangatira Island by establishing 40 permanent forest plots, estimated seabird density through burrow counts, and analysed soil properties. To determine if seabirds were impacting on forest regeneration, we established exclosures (0.25 m²) in 30 of the forest plots, and examined the role of canopy gaps in forest regeneration. The tallest current forest (c. 15 m), dominated by Plagianthus chathamicus, has mostly regenerated since stock were removed in 1959. Mean burrow density was estimated to be 1.19 per square metre, all soils were highly acidic (pH 3.36–5.18), and burrow density was positively correlated with soil phosphorus. Seedling density of woody species in seabird exclosures measured after 9, 24 and 33 months was significantly higher than in the adjacent non-gap plots, and seedling density was positively associated with reduced canopy cover. Seedling densities were also significantly higher in canopy gaps than in adjacent non-gap plots, but seabird burrow density was significantly lower in gaps. These results suggest that canopy gaps allow forest regeneration despite the negative impacts of seabird burrowing. However, the gap makers, largely senescing Olearia traversii, are slowly disappearing from the forests. The cohort of Plagianthus that has regenerated following farm abandonment may progressively collapse, allowing regeneration to continue in small openings, but there is also the potential for a catastrophic blowdown. This might have serious implications for forest-dwelling birds, invertebrates, and plants.     

Behavioural ecology of lonnbergi skuas in relation to environment on the Chatham Islands,New Zealand

Abstract

A population of lonnbergi skuas (family Stercorariidae) was studied over December and January 1974–75 on Rangatira Island, Chatham group (44°22′S,176°11′W). The main aim was to compare the behavioural ecology of these birds with that of maccormicki skuas of Antarctica, and to assess the moderating effect of environment on habits. The skuas held extensive territories along the coast and in inland areas clear of forest and bracken. Five of the 11 study territories were occupied by trios of adult birds. A major effect of the vegetation was to reduce contact between neighbours on the ground at territorial boundaries, and most territorial defence was by aerial display and attack. Eggs were laid from late September, and chicks began flying in late December and January. This breeding schedule is about 2 months earlier than for lonnbergi at Signy Island or for skuas in Antarctica, but falls on a trend line of latitude against egg-laying when all populations are considered. Seventeen chicks were reared on the 11 territories, a breeding success of 1.55 chicks per nest. This high success rate was attributable largely to success in rearing both chicks when two were hatched. This is seldom achieved in more extreme climates, and is apparently determined by the intensity of sibling competitiveness. It is hypothesised that this intensity is graded, and aggression by the older chick of the pair is provoked more easily by food shortage as environmental conditions become increasingly severe. The most important prey items recorded were adult petrels, especially broad-billed prion (Pachyptila vittata vittata) and white-faced storm petrel (Pelagodroma marina maoriana) captured on the ground at night. The skuas were mostly inactive during the day, and were not seen to fish or to chase or harass any other bird on or about the island. Southern blue penguins (Eudyptula minor minor), though very common on the island, were not attacked by the skuas. Skuas were not seen to attempt to dig out petrel or penguin nesting burrows. Of the differences in ecology recorded, only the presence of three adults on territories appears to be characteristic of lonnbergi; it has not been recorded for maccormicki or hamiltoni, and is either unknown or very rare in skua.     

Bacterial Symbiosis in Some New Zealand Plants

A large number of species of Coprasma (Rubiaceae) show bacteria-containingstipular ndules. Hairs which contain bacteria are also present.In other species, for example Myoporum laetum, bacteria arepresent in superficial and in immersed leaf-glands. It is suggestedthat the bacterial symbionts, which can readily be obtainedin culture, may function in the fixation of atmospheric nitrogenand thereby be of importance to the plants when growing in nitrogen-deficientsoils.     

An extinct nestorid parrot (Aves,Psittaciformes, Nestoridae) from the Chatham Islands,New Zealand

We describe an extinct parrot from late Quaternary fossil bone deposits on the Chatham Islands, located c. 800 km east of mainland New Zealand. Mitochondrial DNA analyses and osteological characters confirm that the Chatham Islands parrot was a sister taxon to the New Zealand kaka (Nestor meridionalis Gmelin, 1788). The relatively large femur : humerus length ratio and broad pelvis of the Chatham Islands parrot indicate that it had a more terrestrial habit than the kaka. Stable dietary isotope analyses (δ ¹⁵N and δ ¹³C) of Chatham Islands parrot bones suggest that the species may have been mainly herbivorous, although further analyses are required to confirm this. The presence of Chatham Islands parrot bones in early midden deposits shows that the species persisted into the post‐settlement era, and became extinct possibly as a result of habitat loss, hunting pressure, and rat predation following initial Polynesian settlement of the islands (sometime between the 13^th and 16^th centuries AD). © 2014 The Linnean Society of London     

Differences in habitat selection between Chatham petrels (

The Chatham petrel (Pterodroma axillaris) is an endangered species restricted to a single population on South East Island, Chatham Islands, New Zealand. The key threat to Chatham petrel breeding success is interference with chicks by broad-billed prions (Pachyptila vittata) prospecting for burrows for their oncoming breeding season. This burrow competition has resulted from alteration to breeding habitat by humans throughout the Chatham Islands. Understanding habitat preferences may enable managers to manipulate habitat to reduce burrow competition and will be essential in order to translocate Chatham petrels to a proposed second colony. Habitat characteristics surrounding both Chatham petrel and broad-billed prion burrows were quantified and selection ratios compared. Both Chatham petrels and broad-billed prions selected habitat factors associated with mature forest. Chatham petrels avoided a large number of habitat characteristics, which suggests they were habitat specific, and their preferred habitat is now limited. Broad- billed prions used a wide range of habitat characteristics, which suggests they are not habitat specific. This study recommends that selection values be used when deciding on the best location to establish a second Chatham petrel colony.     

Communally breeding skuas: breeding success of pairs, trios and groups of Catharacta lonnbergi on the Chatham Islands, New Zealand

One-third of territories on South East Island are occupied by trios or groups of communally breeding skuas. Comparisons were made of the reproductive performance of pairs, trios and groups over three (and ten) seasons to assess whether any 'advantage'–in terms of offspring production–could be demonstrated for communal breeding. Egg size was not significantly different between pairs and trios, or between years. There were no significant differences between the chicks of pairs, trios or groups in growth characteristics and chick condition appeared similarly good. Overall breeding success was generally lower for trios than for pairs. Although chick production per territory was not significantly different between pairs and trios, it was substantially lower on a per-adult basis. The breeding success of this population is generally high compared to others studied, however, there is no evidence to suggest that skua communal breeding has advantages in terms of offspring production.     

Heteroblasty on Chatham Island: A comparison with New Zealand and New Caledonia

We used a comparative approach to investigate heteroblasty in the Chatham Islands. Heteroblasty refers to abrupt changes in the morphology of leaves and shoots with plant height. Common on isolated islands such as New Caledonia and New Zealand, which once had flightless, browsing birds, heteroblasty is hypothesised to be an adaptation to deter bird browsing. The Chatham Islands are a small archipelago located 800 km off the east coast of New Zealand, which has clear floristic links to New Zealand. However, unlike New Caledonia and New Zealand, the Chathams never had flightless, browsing birds. We investigated heteroblasty on the Chatham Islands by: (1) comparing height-related changes in leaf morphology and branching architecture in several plant taxa with heteroblastic relatives on the New Zealand mainland; (2) characterising changes in leaf morphology in heteroblastic tree species endemic to the Chathams; and (3) comparing overall trends in leaf heteroblasty on the Chathams with New Caledonia and New Zealand. Reversions to homoblasty were observed in the three Chatham Island taxa with heteroblastic relatives on the New Zealand mainland. However, two endemic tree species were clearly heteroblastic; both produced dramatically larger leaves as juveniles than as adults. Inter-archipelago comparisons showed that this trend in leaf morphology is rare among heteroblastic species in New Caledonia and New Zealand. Therefore, while some of our results were consistent with the hypothesis that heteroblasty is an adaptation to avoid bird browsing, other processes also appear to have shaped the expression of heteroblasty on Chatham Island.     

Human‐mediated extirpation of the unique Chatham Islands sea lion and implications for the conservation management of remaining New Zealand sea lion populations

While terrestrial megafaunal extinctions have been well characterized worldwide, our understanding of declines in marine megafauna remains limited. Here, we use ancient DNA analyses of prehistoric (<1450–1650 AD) sea lion specimens from New Zealand's isolated Chatham Islands to assess the demographic impacts of human settlement. These data suggest there was a large population of sea lions, unique to the Chatham Islands, at the time of Polynesian settlement. This distinct mitochondrial lineage became rapidly extinct within 200 years due to overhunting, paralleling the extirpation of a similarly large endemic mainland population. Whole mitogenomic analyses confirm substantial intraspecific diversity among prehistoric lineages. Demographic models suggest that even low harvest rates would likely have driven rapid extinction of these lineages. This study indicates that surviving Phocarctos populations are remnants of a once diverse and widespread sea lion assemblage, highlighting dramatic human impacts on endemic marine biodiversity. Our findings also suggest that Phocarctos bycatch in commercial fisheries may contribute to the ongoing population decline.     

Non-breeding behaviour of Magenta Petrels Pterodroma magentae at Chatham Island, New Zealand

Magenta Petrels Pterodroma magentae were caught at light-attraction stations on southwest Chatham Island, New Zealand, and most were fitted with transmitters. Of 52 captured since 1993, 71% were males, and all 36 tracked adequately proved to be non-breeders in the breeding season of capture. Our data indicated no sex bias in their probability of being captured at lights. Males provided 86% of trackings, and 87% of trackings of birds flying over the breeding area were males. Males landed 118 times; females 13 times. Only males were found on the ground, by night and day, apparently unassociated with burrows (three with and ten without transmitters), but subsequently digging burrows ( n  = 8). Of 19 birds banded as fledglings up to 2000, males were first recaptured nearing 4 years old (at lights and on the ground) and a female nearing 6 years old (in burrow). Among 37 fledglings, the sex ratio was even. Nine tracked males occupied burrows, as did two females, but the latter were older recaptures (10+ and 25+ years old). It appears that only males claimed existing, or dug new, burrows. They then attracted a mate to the burrow by means unknown, but from among females frequenting an inshore courtship area near the colony, or occasionally flying over the colony, at night. Females established in burrows, but then losing their mate, were able to re-mate there, by calling from near the burrow or by attracting a mate in flight or from the postulated inshore courtship area. Both sexes sometimes took years to pair or re-mate, possibly reflecting the dearth of available mates.     

Lipid composition of the liver oil of deep-sea sharks from the Chatham Rise, New Zealand

Deep-sea sharks approach neutral buoyancy by means of a large liver that contains large amounts of low-density lipids, primarily squalene and diacyl glyceryl ether (DAGE). As an animal increases in size and matures sexually, many biochemical changes take place within the animal. It was hypothesized that maintenance of neutral buoyancy in deep-sea sharks involves fine-scale changes in the chemical composition of the liver oil as individual sharks grow and develop. To test this hypothesis, the lipid composition of liver oil for individuals of different size and sex of deep-sea sharks from the Chatham Rise, New Zealand was compared. The composition of liver oil varied within and among species. Several species contained large amounts of squalene and DAGE, whereas only traces of these lipids were present in other species. The amounts of squalene and DAGE in liver oil were inversely related, and squalene content tended to decrease as sharks increased in size. Species with high squalene levels (>80%) in liver oil were not abundant on the Chatham Rise, although levels of DAGE (a lipid of increasing commercial interest) were elevated in many species. Maintenance of neutral buoyancy in deep-sea sharks appears to involve changes in the composition of low-density liver lipids as the sharks increase in size and mature.     

Pup growth of the New Zealand fur seal Arctocephalus forsteri on the Open Bay Islands, New Zealand

Growth of New Zealand fur seal pups was investigated at Taumaka, Open Bay Islands, New Zealand, from November 1974 to September 1976. Pups were weighed and curvilinear length, axillary girth and foreflipper length measured at about ages 55, 190, 235 and 290 days. Males are significantly heavier and larger than females at each age, wtih the exception of axillary girth at 235 days. Pups born during the austral summer of 1974–5 were smaller overall than were pups born during the following summer. This difference was so great that males aged 140 days in 1976 were larger and heavier than males aged 235 days in 1975. Circumstantial evidence suggests that the difference in growth rates of pups born during the two years may have been a consequence, either directly or indirectly, of environmental temperatures. Pups born during the warmer season (1974–5) had the slower growth.     

A reserve for feral sheep on Pitt Island,Chatham group,New Zealand

Abstract

A scientific reserve of 200 ha has been created on Pitt Island, Chatham Islands for some 300 sheep from a flock of merino origin which has been feral for about 70 years. The reserve has a history of burning-off, and of grazing by cattle, sheep, and pigs. Transects have been established to follow changes in the vegetation. Although the original sheep were white, about 90% of the feral sheep have pigmented fleeces. Self-shedding of the wool is common in the population. The contribution that feral mammals can make to genetic conservation, and the problems that they pose to other conservation priorities, are discussed.     

Some zoosporic fungi of New Zealand

Summary In further studies of the zoosporic fungi of New Zealand nine additional species were isolated on various substrata from soil. These include Rhizophydium pythii de Wildemann, R. condylosum Karling, Rhizophlyctis oceanis Karling, R. ingoldii Sparrow, R. boneysi Sparrow, Rhizophlyctis sp., Rhizidium reniformis sp. nov., Chytriomyces rotoruaensis sp. nov., Sparrowia parasitica Willoughby, and Aphanomycopsis punctatus Karling. Rhizidium reniformis is characterized by predominantly reniform, appendiculate zoosporangia and small zoospores which emerge slowly in a columnar mass. This usually floats away from the zoosporangium and explands, and after a while the zoospores swarm collectively in a vesicle. Chytriomyces rotoruaensis resembles R. reniformis by the structure and appearance of its thallus and behavior of the zoospores after discharge, but differs by the presence of a thin inconspicuous operculum and the development of smooth hyaline resting spores with coarsely granular content. Rhizophlyctis ingoldii, Sparrowia parasitica, and R. boneysi, known previously only from England and Hawaii, respectively, occurred abundantly in New Zealand.This study has been supported by a grant from the National Science Foundation, Washington, D.C.     

Breeding of the bellbird on the Poor Knights Islands,New Zealand

Abstract

The breeding of the bellbird (Anthornis melanura) was studied intensively over three seasons on Aorangi Island, Poor Knights Islands. Adult males defended territories all year but ventured beyond them to exploit localised food resources and to obtain water; some adults defended the same territory for at least 5 years. Adult females shared a territory with a male only during the breeding season. At other times of the year adult females were joined by juveniles and immatures and formed feeding flocks. The breeding season extended from late September to late December. A few nests were built on the ground but most were in dense vegetation, usually near the canopy. Peak egg-laying extended from mid-October to mid-November and only one clutch of two to four eggs was laid. Nest building and incubation were completed by the female alone but both parents fed nestlings. Fledglings stayed in the vicinity of the nest for several days, and were fed by both parents. Incubation and nestling periods were about 15 and 19 days respectively. Comparisons are made with the breeding biology of bellbirds and other native passerines on mainland New Zealand, and the importance of the predator-free enviomment of the Poor Knights Islands is stressed.