The breeding biology of the gadfly petrels Pterodroma spp. of the Pitcairn Islands: characteristics, population sizes and controls

This paper reports the breeding biology and nesting seasons of the gadfly petrels which nest on the four islands of the Pitcairn group, Pitcairn, Henderson, Oeno and Ducie. The species currently breeding are Murphy's petrel Pterodroma ultima , Kermadec petrel P. neglecta , Herald petrel P. heraldica and Henderson petrel P. atrata. Of these, Murphy's petrel is the most numerous; an estimated 250000 pairs bred on Ducie, which is probably the major breeding station of the species. Novel basic breeding data for Murphy's petrel are presented. Incubation spells, averaging 19.3 days, are exceptionally long for a petrel. Phoenix petrel P. alba appears to have ceased to breed on the Pitcairn Islands since the 1922 surveys of the Whitney Expedition. Nesting success was low on Henderson Island during the study. For all four breeding species, less than 20% of eggs laid yielded fledglings. Failure occurred at the early chick stage and observations indicated that it was due to predation by Pacific rats Rattus exulans. Although rats are present on Ducie, predation was apparently less severe there. The situation on Oeno may be intermediate. I consider how the populations of Henderson are maintained in the face of this intense predation. The Murphy's petrel population may be sustained by immigration from Ducie while the Herald and Henderson petrel populations could be undergoing a long-term decline on Henderson. It is not clear how the Kermadec petrel population is maintained. The conservation implications of these findings are discussed.     

The flora of the Pitcairn Islands: a review

vascular plant flora of the Pitcairn Islands, south-central Pacific Ocean, is described based on extensive new collections made in 1991 and previously published records. Two vascular plants occur on Ducie Atoll; one (Pemphis acidula) is a new record. Sixty-three native vascular plants occur on Henderson, of which nine are endemic; Canavalia rosea, Operculina lurpethum, Psilotum nudum and Solanum americanum are new records for the island. Oeno Atoll has 16 native vascular plants; the single endemic (Bidens hendersonensis var. oenoensis) was not found in 1991 despite careful searches. Triumfetta procumbens was new for Oeno. Sixty-six native vascular plants have now been recorded from Pitcairn Island, there are two endemic ferns and seven endemic angiosperms in this number. A number of non-native taxa were new to Pitcairn. Some of the previously described taxa could not be found on Pitcairn, probably because they are very rare and only a small amount of time was spent collecting on Pitcairn. Many of the Pitcairn taxa are threatened by the spread of introduced species, especially Syzygium jambos.     

Seasonality and numbers of green turtles Chelonia mydas nesting on the Pitcairn Islands

During 1991 and 1992 the first regular field observations of green turtles, Chelonia mydas , on the Pitcairn Islands (South Pacific) revealed that nesting occurs only on Henderson where about 10 females laid eggs (c. 1% of the French Polynesian population). Substrates on Pitcairn and Ducie Atoll are unsuitable for nesting and no signs of nesting were found on Oeno Atoll where the terrain appears suitable.     

The fossil birds of Henderson Island, Pitcairn Group: natural turnover and human impact, a synopsis

Recent studies of island biotas have suggested that the impact of man on indigenous flora and fauna is much greater than previously suspected. This impact resulted in the introduction of many new species and the extinction of many unique life-forms. Henderson Island, in the Pitcairn Group, has been found to be an excellent laboratory for the study of natural faunal turnover and the impact of people on the natural environment. This was principally due to the island's remote location and its limestone structure, which resulted in the excellent preservation of fossil remains. During the Sir Peter Scott Commemorative Expedition to the Pitcairn Islands, extensive excavations were undertaken resulting in the collection of 42213 bird bones. It was possible to identify 31%. Of the 31 taxa identified, four seabirds appear to be vagrants, a surprisingly high number illustrating that the uncritical evaluation of fossil bird lists from other islands risks over-estimating the number of indigenous species. As a result of the arrival of Polynesian people during the first half of this millennium, half of Henderson's endemic landbirds became extinct, as did most of the small ground-nesting seabirds. The lower sea level during cold stages creates many temporary limestone 'high' islands. This results in many 'former-atolls' developing geological and ecological similarity to Henderson. Hence lower sea-level greatly facilitates the movement of flora and fauna between currently isolated oceanic 'high' islands.     

The Foraminifera of the Pitcairn Islands

Foraminifera were recovered from 18 samples collected in the Pitcairn Islands, 12 from Henderson Island (including the best and most comprehensive collections) and three each from Oeno Atoll and Pitcairn Island itself. Although both algae and sediment samples were collected, the living Foraminifera came, almost exclusively, from phytal (attached or clinging) habitats. Foraminifera in the sediment samples are mainly thanatocoenoses. The fauna is an exclusively calcareous, relatively low diversity assemblage, dominated by large soritids [Marginopora, Amphisorus, Sorites) and Amphistegina , all of which are ubiquitous throughout the tropical Pacific. These larger Foraminifera are usually accompanied by small miliolids in particular, as well as by small attached Foraminifera (discorbids and the like). Typical reefal Foraminifera are generally under-represented. So far, no endemic species have been found. Of more significance, perhaps, is the apparent absence of Calcarina , small rotaliids, elphidiids and agglutinating species, so common in the western Pacific islands. One sample of fossil Foraminifera was analysed, from a shelly sand (c. 30 m above present sea-level) on Henderson Island. Though, for the most part, like the Recent assemblages, this was characterized by Archaias , a soritid which was not found in any of the modern collections made by the 1991– 92 Expedition. This could either be a sampling artifact or refer to a real environmental change since the Pleistocene.     

The phytogeographical affinities of the Pitcairn Islands – a model for south‐eastern Polynesia?

Aim To identify how the Pitcairn group relates biogeographically to the south‐eastern Polynesian region and if, as a subset of the regions flora, it can then be used as a model for biogeographical analyses. Location The Pitcairn group (25°4′ S, 130°06′ W) comprises four islands: Pitcairn, a relatively young, high volcanic Island; Henderson, an uplifted atoll, the uplift caused by the eruption of Pitcairn; and two atolls, Ducie and Oeno. The remote location, young age and range of island types found in the Pitcairn Island group makes the group ideal for the study of island biogeography and evolution. Methods A detailed literature survey was carried out and several data sets were compiled. Dispersal method, propagule number and range data were collected for each of the 114 species that occurs in the Pitcairn group, and environmental data was also gathered for islands in Polynesia. Analyses were carried out using non‐metric multidimensional scaling and clustering techniques. Results The flora of the Pitcairn Islands is derived from the flora of other island groups in the south‐eastern Polynesian region, notably those of the Austral, Society and Cook Islands. Species with a Pacific‐wide distribution dominate the overall Pitcairn group flora. However, each of the islands show different patterns; Pitcairn is dominated by species with Pacific, Polynesian and endemic distributions, with anemochory as the dominant dispersal method (39.5%); Henderson is also dominated by species with Pacific, Polynesian and endemic distributions, but zoochory is the dominant dispersal method (59.4); Oeno and Ducie are dominated by Pantropic species with hydrochory as the most common dispersal method (52.9% and 100%, respectively). Main conclusions ? Habitat availability is the most significant factor determining the composition and size of the flora. ? South‐east Polynesia is a valid biogeographical unit, and should include the Cook, Austral, Society, Marquesas, Gambier, Tuamotu and Pitcairn Islands with Rapa, but should exclude Easter Island, Tonga and Samoa. ? Regionalization schemes should take island type into consideration. ? The Pitcairn Island group can serve as a useful model for Pacific biogeographical analyses.     

The evolution of north‐east Atlantic gadfly petrels using statistical phylogeography

Macaronesia (north‐east Atlantic archipelagos) has been host to complex patterns of colonization and differentiation in many groups of organisms including seabirds such as gadfly petrels (genus Pterodroma). Considering the subspecies of widely distributed soft‐plumaged petrel for many years, the taxonomic status of the three gadfly petrel taxa breeding in Macaronesia is not yet settled, some authors advocating the presence of three, two or one species. These birds have already been the subject of genetic studies with only one mtDNA gene and relatively modest sample sizes. In this study, using a total of five genes (two mitochondrial genes and three nuclear introns), we investigated the population and phylogeographical histories of petrel populations breeding on Madeira and Cape Verde archipelagos. Despite confirming complete lineage sorting with mtDNA, analyses with nucDNA failed to reveal any population structuring and Isolation with Migration analysis revealed the absence of gene flow during the differentiation process of these populations. It appears that the three populations diverged in the late Pleistocene in the last 150 000 years, that is 10 times more recently than previous estimates based solely on one mtDNA gene. Finally, our results suggest that the Madeira petrel population is ancestral rather than that from Cape Verde. This study strongly advocates the use of nuclear loci in addition to mtDNA in demographical and phylogeographical history studies.     

Managing the Effects of Introduced Predators on Hawaiian Endangered Seabirds

Introduced predators are one of the greatest threats facing seabirds worldwide. We investigated the effects of multiple introduced predators on 2 endangered seabirds, the Newell's shearwater (Puffinus newelli) and the Hawaiian petrel (Pterodroma sandwichensis), on the island of Kauaʻi, Hawaiʻi, USA. Between 2011 and 2017, we recorded 309 depredations of which 35.6% were by feral cats, 50.2% by black rats (Rattus rattus), 10.4% by pigs (Sus scrofa; feral pigs), and 3.9% by barn owls (Tyto alba). Cats were the most destructive of the predators because they killed more breeding adults than chicks, which had repercussions on breeding probability in following years. Cats and rats were also the most prevalent of all the predators, depredating birds at all of the sites under consideration regardless of how remote or inaccessible. We also considered the effectiveness of predator control over the study period. Reproductive success at all sites increased once predator control operations were in place and depredations by all species except barn owls decreased. Furthermore, we modeled population trajectories for all sites with and without predator control. Without predator control, population trajectories at all sites declined rapidly over 50 years. With predator control operations in place, populations at all sites increased; thus, controlling introduced predators at endangered seabird colonies is important for their management. © 2020 The Wildlife Society.     

Systematic review of the land snails of the Pitcairn Islands

The land snails (and semi-terrestrial molluscs) of the four islands that comprise the Pitcairn group are reviewed and the indigenous species illustrated. The strictly terrestrial molluscan faunas from the two atolls (Oeno and Ducie) are poor, like many other atolls in the Pacific. Each supports less than six species with wide geographical ranges. In contrast, the terrestrial molluscan fauna from Henderson Island, an uplifted atoll, is more diverse with at least 16 species belonging to seven families. Over half these taxa appear to be endemic, at least at the level of sub-species. Two species of semi-terrestrial molluscs have also been found on Henderson. Analyses of archaeological deposits in caves near the North Beach have revealed that at least a further six species of land snail formerly occurred on Henderson. The volcanic island of Pitcairn, the only island in the group still inhabited, supports the greatest number of terrestrial molluscs. Twenty-six species of land snail (and one semi-terrestrial pulmonate) were found living there during the recent expedition and a further three taxa were recognized amongst museum material. At least seven of these species are thought to be recent adventives and a further three are likely to have been prehistoric introductions. One Henderson (Georissa hendersoni) and three Pitcairn endemics (Pacificella filica, Sinployea pitcaimensis and Diastole tenuistriata) are formally described as new species. Some of the Pitcairn endemics occur in very restricted areas (less than a hectare) and it is important that measures should be taken to prevent the spread of invasive plants, such as rose-apple, that would threaten their survival.     

The composition and relationships of the marine molluscan fauna of the Pitcairn Islands

The recent expedition has doubled the number of marine molluscs known from the Pitcairn Islands. Over 80 taxa are recorded from Ducie and Pitcairn (both still poorly known), 240 from Oeno and 320 from Henderson. A total exceeding 400 taxa is now known from the group as a whole. Most of this increase results from a vastly improved knowledge of the small taxa that had been neglected in earlier surveys. Important faunal differences exist between the four islands in the group which are related to the different character of each island. These totals still underestimate the true diversities, but they provide data that are comparable in quality to those from adjacent regions. In this context the molluscan fauna from the Pitcairn Islands is seen to be impoverished when compared to those from islands further west. Most of the fauna is composed of widespread Indo-West Pacific species, but there are several taxa that have more restricted ranges centred on S.E. Polynesia. A few, including some undescribed taxa discovered on the expedition, appear to be endemic. Significantly, many of these are characterized by non-planktotrophic larval development. Comparison of the modern fauna from Henderson with the fossil fauna from the Pleistocene reef on its plateau reveals important differences. About 25% of the fossil molluscs are currently unknown from the group and about 5% appear to be undescribed. These high rates of turnover demonstrate that the faunas are temporally unstable.     

A conservation appraisal of the rare and endemic vascular plants of Pitcairn Island

The flora of the Pitcairn Islands consists of 81 species, of which 10 are endemic. IUCN Red List threat categories show that over 60% of the indigenous flora is threatened within the island, and over 20% is threatened globally. To provide a more objective regional assessment that could prioritise conservation management, a system of threat scores was applied to each taxon based on potential threat due to habitat damage or exploitation. The main threats affecting the flora and vegetation are posed by habitat clearance, spread of invasive species, small population sizes or restricted distributions, erosion, lack of a frugivorous bird and exploitation. Addressing these threats by means of a system of nature reserves, species-specific recovery plans and control of invasive species, erosion and exploitation, will start to combat these problems. However, any conservation activities must be implemented in conjunction with the interests of the local community, and in consultation with them, in order to ensure success.     

The Pitcairn Islands, South Pacific Ocean: plate tectonic and climatic contexts

The remote Pitcairn Group in the South Pacific Ocean comprises a volcanic island (Pitcairn Island), two low coral atolls (Oeno, Ducie) and a raised coralline island (Henderson Island). The geological history of these islands, on anomalously thin oceanic lithosphere, is related to the development of two subparallel island chains (Oeno-Henderson-Ducie; Pitcairn) associated with intra-Pacific plate 'hotspot' activity; the surface manifestation of this activity has been partly determined by structural lineations in the plate inherited from past plate history. The climate of the Pitcairn Islands is determined by the position of the subtropical high pressure system and the South Pacific Convergence Zone. Variations in the strength of this atmospheric circulation system, measured by changes in the Southern Oscillation index of pressure difference, provide a partial explanation of the long-term variability of mean annual rainfall at Pitcairn Island. Knowledge of past climates in the Pitcairn Group remains speculative. Maps of the Pitcairn Islands and a report of climate at Henderson Island (2/91-1/92) are included in the paper.     

An assessment of the breeding range,colony sizes and population of the Westland petrel (Procellaria westlandica)

Abstract

The Westland petrel (Procellaria westlandica) is an endemic New Zealand species and one of the very few burrowing seabird species still breeding on mainland New Zealand. It nests only on a series of coastal ridgelines near to Punakaiki on the West Coast of the South Island. Between 2002 and 2005, surveys were undertaken at 28 of the 29 known colonies. The area occupied by the colonies was 73 ha; most colonies had fewer than 50 burrows, but six colonies had 201–500 burrows and four colonies had more than 1000 burrows. We find that the current breeding range of Westland petrel and the location of individual colonies are similar to those reported in both the 1950s and 1970s. Based on total burrow counts at 28 colonies and burrow occupancy rates determined by annual monitoring, the annual breeding population is estimated to be between 2954 and 5137 breeding pairs.     

Systematics of the extinct reed warblers Acrocephalus of the Society Islands of eastern Polynesia

In the Society archipelago (French Polynesia), Acrocephalus reed warblers are known only from four islands: Tahiti, Mo'orea, Huahine and Raiatea. All populations are now extinct except on Tahiti. Our knowledge of these birds is based on a small number of specimens preserved in museums, collected mostly during the 19th century. We present here a review of the past and present distribution, habitat and threats to the Society Islands reed warblers, including details on the specimens in museum collections. We compare the external morphology of the different populations, and use samples from museum specimens to propose a molecular phylogeny of all taxa based on partial cytochrome b gene sequences. The genetic data do not support the monophyly of the Society Islands reed warblers, which probably derived from three different lineages, found in Tahiti, Mo'orea and in the cluster Raiatea–Huahine. We outline the taxonomic consequences of this phylogeny. Our results support the hypothesis that evolutionary pattern, not distance between islands, shaped the long-distance colonization of oceanic islands by reed warblers.     

Consistent concentrations of critically endangered Balearic shearwaters in UK waters revealed by at‐sea surveys

AimEurope''s only globally critically endangered seabird, the Balearic shearwater (Puffinus mauretanicus), is thought to have expanded its postbreeding range northwards into UK waters, though its at sea distribution there is not yet well understood. This study aims to identify environmental factors associated with the species’ presence, map the probability of presence of the species across the western English Channel and southern Celtic Sea, and estimate the number of individuals in this area.LocationThe western English Channel and southern Celtic Sea.MethodsThis study analyses strip transect data collected between 2013 and 2017 from vessel‐based surveys in the western English Channel and southern Celtic Sea during the Balearic shearwater''s postbreeding period. Using environmental data collected directly and from remote sensors both Generalized Additive Models and the Random Forest machine learning model were used to determine shearwater presence at different locations. Abundance was estimated separately using a density multiplication approach.ResultsBoth models indicated that oceanographic features were better predictors of shearwater presence than fish abundance. Seafloor aspect, sea surface temperature, depth, salinity, and maximum current speed were the most important predictors. The estimated number of Balearic shearwaters in the prediction area ranged from 652 birds in 2017 to 6,904 birds in 2014.Main conclusionsAreas with consistently high probabilities of shearwater presence were identified at the Celtic Sea front. Our estimates suggest that the study area in southwest Britain supports between 2% and 23% of the global population of Balearic shearwaters. Based on the timing of the surveys (mainly in October), it is probable that most of the sighted shearwaters were immatures. This study provides the most complete understanding of Balearic shearwater distribution in UK waters available to date, information that will help inform any future conservation actions concerning this endangered species.     

Relative influence of fisheries and climate on the demography of four albatross species

Worldwide ecosystems are modified by human activities and climate change. To be able to predict future changes, it is necessary to understand their respective role on population dynamics. Among the most threatened species are top predators because of their position in the food web. Albatross populations are potentially affected by both human activities, especially longline fisheries, and climatic fluctuations. Based on long‐term data (1985–2006), we conducted through a comparative approach a demographic analysis (adult survival and breeding success) on four albatross species breeding on the Indian Ocean sub‐Antarctic Islands to assess the relative impact of climate and fisheries during and outside the breeding season. The study revealed that adult survival of almost all species was not affected by climate, and therefore probably canalized against climatic variations, but was negatively affected by tuna longlining effort in three species. Breeding success was affected by climate, with contrasted effects between species, with Southern Oscillation Index having an impact on all species but one. Differences in demographic responses depended on the foraging zone and season. In order to predict population trajectories of seabirds such as albatrosses, our results show the importance of assessing the relative influence of fishing and climate impacts on demography.