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.     

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.     

Some Differences between Plants of the Chatham Islands and the New Zealand Mainland

A number of Chatham Island plants show morphological differences from related plants on mainland New Zealand. These differences could have arisen as a result of freedom from moa browsing on the Chatham Islands. A possible test for this hypothesis is suggested.     

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     

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.     

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.     

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.     

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.     

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.     

Distribution and abundance of fish in a rocky reef environment at the subantarctic Auckland Islands,New Zealand

Summary The distribution and abundance of fish in a rocky reef environment were investigated at the subantarctic Auckland Islands of New Zealand, in June 1986. Fish were counted in transects and specimens were taken. The diversity and abundance of species of large reef fish was low; a total of eight species were observed. Most fish were benthic carnivores. These findings are similar to studies of reef fish in subantarctic waters of Chile. Large differences in species composition were found among locations at the Auckland Islands. The number of species and their abundance was highest near exposed headlands. Few fish were found on reefs at more sheltered inlets. At most locations the nototheniids Paranotothenia angustata and P. microlepidota ranked first in abundance at deep and shallow sites. There were some species that showed differences in abundance with depth. Highest abundance of Bovichthys variegatus, Latridopsis cilaris, Latris lineata and Pseudolabrus cinctus were in deep water on reefs. Large numbers of juvenile P. microlepidota were found only in shallow water. No depth related patterns were found for P. angustata and Mendosoma lineatum. Specimens, other than those counted in transects, were also collected. There were small fish, 4 species of tripterygiids, 1 gobiescocid and 2 syngnathids. The Auckland Islands had closer zoogeographic affinities with islands of temperate and subantarctic New Zealand than with other landmasses of the westwind drift. Although most fish found at the Auckland Islands are found also in temperature New Zealand, the converse of this pattern was not found. The proportional representation of species and trophic groups differed markedly between these regions.     

Germination ecology of coastal plants in relation to salt environment

Responses of seed germination to salinity were examined using 37 species collected from salt marshes, cliffs, and fore (unstable) and hind (stable) sand dunes along Japanese coasts. For comparison, seed germination of nine inland species was also examined. The soil salinities in salt marshes ranged from 150 to 300 mmol/L NaCl, whereas those in fore and hind dunes ranged from 0 to 150 mmol/L NaCl, with a few exceptions. Cliff soils showed relatively high salinities up to 300 mmol/L NaCl. Ciff and foredune soils that encountered a typhoon and storm showed high salinities >300 mmol/L NaCl. Salt tolerance in seed germination of coastal plants was ordered by comparing the responses of percentage and rate of germination to salinity conditions up to 200 mmol/L NaCl, being in the order of salt marsh>cliff>foredune≅hind dune≅inland. Thse results indicate that salt tolerance in seed germination of coastal plants is closely related to the salinity conditions of their habitats. Germination experiments under favorable conditions showed that a high percentage of the seeds of salt marsh species germinate rapidly, those of diff species germinate slowly and those of foredune species exhibit a low percentage and low rate of germination. It seems that these germination characteristics contribute to the success of germination at the ‘safe site’ and the subsequent survivorship of emerged plants in their natural habitats.     

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.     

Behavioural flexibility predicts invasion success in birds introduced to New Zealand

A fundamental question in ecology is whether there are evolutionary characteristics of species that make some better than others at invading new communities. In birds, nesting habits, sexually selected traits, migration, clutch size and body mass have been suggested as important variables, but behavioural flexibility is another obvious trait that has received little attention. Behavioural flexibility allows animals to respond more rapidly to environmental changes and can therefore be advantageous when invading novel habitats. Behavioural flexibility is linked to relative brain size and, for foraging, has been operationalised as the number of innovations per taxon reported in the short note sections of ornithology journals. Here, we use data on avian species introduced to New Zealand and test the link between forebrain size, feeding innovation frequency and invasion success. Relative brain size was, as expected, a significant predictor of introduction success, after removing the effect of introduction effort. Species with relatively larger brains tended to be better invaders than species with smaller ones. Introduction effort, migratory strategy and mode of juvenile development were also significant in the models. Pair-wise comparisons of closely related species indicate that successful invaders also showed a higher frequency of foraging innovations in their region of origin. This study provides the first evidence in vertebrates of a general set of traits, behavioural flexibility, that can potentially favour invasion success.     

Population ecology of Mus musculus on Mana Island, New Zealand

Feral house mice ( Mus musculus ) living on 217 ha Mana Island, New Zealand, with no mammalian predators, were snap-trapped and autopsied. A 7-month breeding season took the population from a spring low to extremely high density in autumn. Litters were largest in the middle of the breeding season, and significantly larger on Mana than on the New Zealand mainland. Litter size in early pregnancy was similar for young and old mice but more embryos were resorbed by old females. The breeding season ended in April when adult females stopped ovulating and young failed to mature. When the population declined over winter no animals bred, they all lost weight, and even previously mature males lost their reproductive ability. Mice continue to grow throughout life and become larger than mice in most populations on the New Zealand mainland. The regular and pronounced seasonal pulse in Mana's mouse population contrasts with longer-term fluctuations generally seen in mainland populations at lower density in indigenous forest. These differences may be explained by absence of predators, habitat features or lack of any chance to disperse on the island.     

Variability in the diet of New Zealand sea lion (Phocarctos hookeri) at the Auckland Islands, New Zealand

We examined the stomach contents of 121 New Zealand (NZ) sea lions ( Phocarctos hookeri ) caught by the squid fishery during the summer/autumn 1997–2006 around the Auckland Islands (51°S, 166°E). Dietary variation was assessed among juveniles, lactating females, nonlactating females and males, and between areas on the Auckland Islands shelf. The digested fraction of the contents consisted mostly of opalfish ( Hemerocoetes spp.) (50.1% by number [ N ], 4.7% by mass [ M ]), rattail ( Coelorinchus spp.) (12.0% N , 2.4% M ), arrow squid ( Nototodarus sloani ) (14.1% N , 17.9% M ), octopus ( Enteroctopus zealandicus ) (2.1% N , 27.8% M ), and red cod ( Pseudophycis bachus ) (3.8% N , 4.3% M ). Opalfish was found in greater proportions in the stomachs of females (lactating: 58.1% N , nonlactating: 62.4% N ) and juveniles (56.9% N ) than males (14.5% N ). Juveniles caught smaller opalfish and rattail than adults did. Over all classes, sea lions ate larger prey in the east than in the north of the Auckland Islands shelf. The common prey—arrow squid and rattail—constitute an abundant resource at the edges of the Auckland Islands shelf, where lactating NZ sea lions forage. Although these key areas are far from the rookeries and impacted by the squid fishery, they may provide the only reliable resource able to support the cost of benthic foraging behavior in the deepest diver of all otariids.     

Behavioural response thresholds in New Zealand crab megalopae to ambient underwater sound

A small number of studies have demonstrated that settlement stage decapod crustaceans are able to detect and exhibit swimming, settlement and metamorphosis responses to ambient underwater sound emanating from coastal reefs. However, the intensity of the acoustic cue required to initiate the settlement and metamorphosis response, and therefore the potential range over which this acoustic cue may operate, is not known. The current study determined the behavioural response thresholds of four species of New Zealand brachyuran crab megalopae by exposing them to different intensity levels of broadcast reef sound recorded from their preferred settlement habitat and from an unfavourable settlement habitat. Megalopae of the rocky-reef crab, Leptograpsus variegatus, exhibited the lowest behavioural response threshold (highest sensitivity), with a significant reduction in time to metamorphosis (TTM) when exposed to underwater reef sound with an intensity of 90 dB re 1 μPa and greater (100, 126 and 135 dB re 1 μPa). Megalopae of the mud crab, Austrohelice crassa, which settle in soft sediment habitats, exhibited no response to any of the underwater reef sound levels. All reef associated species exposed to sound levels from an unfavourable settlement habitat showed no significant change in TTM, even at intensities that were similar to their preferred reef sound for which reductions in TTM were observed. These results indicated that megalopae were able to discern and respond selectively to habitat-specific acoustic cues. The settlement and metamorphosis behavioural response thresholds to levels of underwater reef sound determined in the current study of four species of crabs, enables preliminary estimation of the spatial range at which an acoustic settlement cue may be operating, from 5 m to 40 km depending on the species. Overall, these results indicate that underwater sound is likely to play a major role in influencing the spatial patterns of settlement of coastal crab species.