Westland Petrel Research Articles

The biogeochemistry and ecological impact of Westland petrels (Procellaria westlandica) on terrestrial ecosystems

The Westland petrel (Procellaria westlandica) is a 1200 g medium-sized seabird whose breeding colonies are dispersed across 700 ha of forest on the western coast of South Island, New Zealand. These birds represent the sole landscape-scale lowland remnant of formerly widespread petrel and shearwater colonies in mainland New Zealand and provide an opportunity to investigate maritime species’ impact on terrestrial ecosystems characteristic of pre-human New Zealand.

A new fossil species of Procellaria (Aves: Procellariiformes) from the Pliocene of New Zealand

We describe a new Procellaria petrel species from the late Pliocene of Taranaki, New Zealand. The new species is most similar morphologically to the White-Chinned Petrel (P. aequinoctialis), Spectacled Petrel (P. conspicillata) and the Westland Petrel (P. westlandica). Compared with those taxa, the new species has a deeper and shorter premaxilla, longer coracoid and shorter wings, while its legs are a similar size. Today, New Zealand is the centre of global diversity of the genus, with four breeding species. This is the first fossil species of Procellaria to be described from New Zealand, attesting to a reasonably long history of this genus in the region.

Foraging niche overlap during chick-rearing in the sexually dimorphic Westland petrel.

Most Procellariform seabirds are pelagic, breed in summer when prey availability peaks, and migrate for winter. They also display a dual foraging strategy (short and long trips) and sex-specific foraging. The Westland petrel Procellaria westlandica, a New Zealand endemic, is one of the rare seabirds breeding in winter. Preliminary findings on this large and sexually dimorphic petrel suggest a foraging behaviour with no evidence of a dual strategy, within a narrow range and with shared areas between sexes. To investigate further this unusual strategy, the present study determined the fine-scale at-sea behaviours (global positioning system and accelerometer data loggers) and trophic niches (stable isotopes in whole blood) of chick-rearing individuals (16 males and 13 females). All individuals foraged on the shelf-slope of the west coast of New Zealand's South Island with short, unimodal trips. Both sexes foraged at similar intensity without temporal, spatial or isotopic niche segregation. These findings suggest the presence of a winter prey resource close to the colony, sufficient to satisfy the nutritional needs of breeding without increasing the foraging effort or intra-specific competition avoidance during winter. Additional data are needed to assess the consistency of foraging niche between the sexes and its reproductive outcomes in view of anticipated environmental changes.

Environmental factors and fisheries influence the foraging patterns of a subtropical seabird, the Westland Petrel (Procellaria westlandica), in the Tasman Sea

ABSTRACT Environmental and anthropogenic influences in the marine environment are primary drivers of behavior and demographic outcomes for marine birds. We examined factors influencing the foraging patterns of the Westland Petrel (Procellaria westlandica), a highly threatened, endemic petrel that inhabits subtropical water masses primarily in the Tasman Sea, with a poorly known at-sea distribution. Risk assessments place the species at moderate risk of population impacts from fisheries-related mortality. Studies in the 1990s indicated that trawl fisheries would have an important influence on the Westland Petrel's foraging behavior. We investigated the influence of climatic conditions, marine productivity, bathymetry, the core fishery zone, concurrent fishing activity, light conditions, sex, and breeding stage on Westland Petrel foraging patterns. We analyzed the stable isotopes of carbon and nitrogen from blood sampled during the incubation period and examined changes in isotopic niche width over a 6-yr p...

Forest stream biota carbon : nitrogen ratios are unaffected by nutrient subsidies from breeding Westland petrels (Procellaria westlandica)

Stable isotope studies have repeatedly shown marine nutrient incorporation from seabirds, anadromous fish and tidal wrack into terrestrial and freshwater ecosystems. However, little is known about the physiological consequences of marine-derived nutrient subsidies. Protein content and lipid storage are important physiologically, and the C:N ratio is a widely used proxy that reflects changes in these quantities. In this study we tested the response of C:N ratios in stream biota to the presence of marine-derived nutrients from Westland petrels, a forest breeding seabird. Samples of different stream invertebrate functional feeding groups, predatory freshwater fish, coarse particulate organic matter and riparian soil and vegetation came from four reference streams and four streams with a wide range of seabird densities. Samples were analysed for percentage C, percentage N and δ15N using isotope ratio mass spectrometry. The data were tested against petrel colony size, stream size and distance from colony to sampling site. Despite increased δ15N accompanying petrel presence (as reported previously), Westland petrels had no effect on stream biota C:N ratios, regardless of colony presence or absence or colony size. Despite the nutrients provided by petrels, we conclude that petrel N replaced rather than enhanced non-marine N in these stream ecosystems.

Minimal ecosystem uptake of selenium from Westland petrels, a forest-breeding seabird

Endemic Westland petrels (Procellaria westlandica) are a remnant of extensive seabird populations that occupied the forested hill country of prehuman New Zealand. Because seabird guano is rich in Se, an often-deficient essential element, we proposed that Westland petrels enhance Se concentrations in ecosystems associated with their breeding grounds. We sampled terrestrial (soil, plants, riparian spiders) and freshwater (benthic invertebrates, fish) components from Westland petrel-enriched and non-seabird forests on the western coast of New Zealand's South Island, an area characterised by highly leached, nutrient-poor soils. Median seabird soil Se was an order of magnitude higher than soil from non-seabird sites (2.2mgkg−1 compared to 0.2mgkg−1), but corresponding plant foliage concentrations (0.06mgkg−1; 0.05mgkg−1) showed no difference between seabird and non-seabird sites. In streams, Se ranged from 0.05mgkg−1 (riparian foliage) to 3.1mgkg−1 (riparian spiders and freshwater mussels). However, there was no difference between seabird and non-seabird streams. Stoichiometric ratios (N:Se, P:Se) showed Se loss across all ecosystem components relative to seabird guano, except in seabird colony soil where N was lost preferentially. Seabirds therefore did not enrich the terrestrial plants and associated stream ecosystems in Se. We conclude that incorporation of trace elements brought ashore by seabirds cannot be assumed, even though seabirds are a significant source of marine-derived nutrients and trace elements to coastal ecosystems world-wide.

Modeling the demography and population dynamics of a subtropical seabird, and the influence of environmental factors

ABSTRACT The use of long-term ecological datasets to explore the importance of the effects of environmental variability on higher predator populations has been focused mainly on high-latitude areas. We modeled the population dynamics of the Westland Petrel (Procellaria westlandica), which spends its time mostly in subtropical waters during both breeding and the interbreeding migration across the Pacific Ocean. We found that the population has slowly increased since the early 1970s, a result of high adult survival, high fecundity (0.6 of all eggs laid survived to fledge) and moderate mean age at first return to the colony (7.7 yr; a recruitment age typical for this genus), strong recruitment rate of juveniles, and negligible emigration. The modeled population trends were supported by similar rates of increase in nest occupancy since 2001 and nest density since 2007. Annual adult survival for breeders was the same for both sexes (0.954, 95% CI: 0.918–0.975) and constant across years. However, nonbreeders ha...

Microbial carbon concentration in samples of seabird and non-seabird forest soil: Implications for leaf litter cycling

Abstract The paucity of leaf litter in seabird forest is usually explained by litter burial in burrows, but burial by itself fails to address the processes controlling decomposition. We measured soil microbial C in samples from a Westland petrel ( Procellaria westlandica ) colony both within and outside the breeding season, and compared the results with two non-seabird forests. From the few studies of seabird soil microbial C, we initially hypothesised a soil microbial C concentration sequence of occupied burrows > unoccupied burrows > adjacent forest floor > non-seabird forest. Instead, the highest values came from non-seabird forest, a pattern consistent with published meta-analyses on the effects of N addition. Within the colony, highest concentrations were in forest floor soil and there was no burrow occupation effect. However, seabird forest soil microbial C followed a strong inverse relationship with soil δ 13 C ( r = −0.58; P r = 0.75); the relationship with soil δ 13 C in non-seabird forest was not significant ( P = 0.29). We propose that soil microbes in seabird forest repeatedly process a single pool of increasingly refractory terrestrial soil C, facilitated by seabird guano priming of organic matter mineralisation. In this context, the paucity of leaf litter in seabird forest can be seen as a consequence of microbial C limitation in a nutrient-saturated system, an explanation consistent with recent theory.

Tori‐lines with weighted branch lines reduce seabird bycatch in eastern South Pacific longline fishery

Abstract The effectiveness of tori‐lines combined with double‐weighted branch lines in reducing seabird bycatch was evaluated in a pelagic longline fishery. Seabird bait attack behaviour, bycatch number, and sinking rate of baited hooks were examined on double‐weighted and unweighted branch lines deployed on the same longline with a single tori‐line. Comparisons were conducted from July to October in 2011 during two cruises on a chartered longline vessel in the eastern South Pacific Ocean outside the Chilean and Peruvian exclusive economic zones. Cape petrels (Daption capense), white‐chinned petrels (Procellaria aequinoctialis) and Westland petrels (Procellaria westlandica) were abundant during line setting. There were 275 primary bait‐taking attacks by these species, but there were only eight primary attacks by albatrosses. Nevertheless, six albatrosses and six diving seabirds were incidentally caught as bycatch. Of the primary attacks by Cape petrels, white‐chinned petrels and Westland petrels, 153 led to secondary attacks. These results suggest that off Chile and Peru there is frequent secondary bycatch of albatrosses as a result of their stealing bait from Cape petrels and diving seabirds. Best‐fit models for the number of primary attacks and of bycatch included the weighted branch line; the use of weighted branch lines resulted in a lower number of primary attacks. Hooks on unweighted branch lines did not reach any of the benchmark depths (3, 5, and 10 m) within the aerial extent of the tori‐lines (the tori‐line remaining above the water surface), hooks on weighted branch lines reached 5 m depth within the aerial extent. These results suggest that, for the pelagic longline fishery off Chile and Peru, combining double‐weighted branch lines and tori‐lines reduces the bycatch more effectively than tori‐lines with unweighted branch lines. Copyright © 2014 John Wiley & Sons, Ltd.

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

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.

Breeding Westland petrels as providers of detrital carbon and nitrogen for soil arthropods: a stable isotope study

Seabirds deposit large quantities of marine detritus on land, but little is known of the soil arthropods processing this material. Burrow-nesting seabirds concentrate their activities within their burrows, so we tested the hypothesis that burrow arthropod fauna is more marine-like in its isotopic enrichment (13C/12C, 15N/14N; expressed as δ13C and δ15N) than the arthropods on the adjacent forest floor. Results from a Westland petrel (Procellaria westlandica) colony on the South Island of New Zealand did not support the hypothesis. Instead, δ15N was universally marine (13–22‰). While δ13C separated into two clusters, the distribution was not according to arthropod provenance. Most taxa had a terrestrial δ13C; only two taxa (a leiodid beetle and the mesostigmatic mite Ayersacarus woodi) incorporated marine C. The leiodid beetle occurs both in burrows and on the forest floor; beetles from both habitats had a marine δ13C. Ayersacarus woodi is found only in burrows. We conclude that, in this system, marine and terrestrial detrital C is processed separately, and that marine detrital C enters the terrestrial ecosystem through a very few arthropod taxa.

Soil selenium in a forested seabird colony: distribution, sources, uptake by plants, and comparison with non-seabird sites

Seabirds vector selenium (Se) into terrestrial ecosystems in Antarctica and on tropical coral islands, but factors controlling distribution within affected soils are unknown, especially in temperate regions. At a Westland petrel (Procellaria westlandica) breeding colony on mainland New Zealand, the concentration of Se in petrel guano (3.6 mg kg–1) exceeded soil parent material (0.8 mg kg–1) and in all but two soil samples (range 1.2–4.2 mg kg–1; n = 52). External Se (Se not derived from parent material) accounted for 64 ± 9% (mean ± s.d.) of soil Se. Measurements were also made at a former seabird breeding site, and at a site with no Holocene seabird breeding. Median surface-soil Se concentrations (mg kg–1) were in the order burrow soil (2.6) > adjacent forest floor (2.2) > former breeding site (1.0) > control site (0.2), with significant differences between burrow soil and (1) the former breeding site and (2) the control site. In a linear regression model, soil pH, and δ15N were the only significant predictors of external Se in colony soil. The correlations are consistent with seabird input driving both the Se supply and increased sorptive uptake in an environment acidified by seabird guano. Despite the enhanced Se in colony soil, median foliage concentrations (tree fern 0.05 mg kg–1, nikau 0.08 mg kg–1) were close to the accepted minimum for herbivore nutrition. Seabirds therefore contribute significant Se to breeding colony soils in temperate areas, but this is not necessarily transferred to plant foliage.

Gender Assignment of Westland Petrels (Procellaria westlandica) Using Linear Discriminant Function Analysis

Abstract Rapid classification of a study subject's gender is critical for many ecological, behavioral, and conservation projects. We evaluated sexual-size dimorphism of adult Westland Petrels (Procellaria westlandica), a large nocturnal colony-nesting seabird, using linear discriminant function analysis and compared our results to birds classified using standard DNA gender identification techniques. The results revealed a strong pattern of sexual dimorphism (Wilks' Lambda = 0.43, F7,29 = 5.6, P < 0.001) in the standard discriminant function analysis despite an unbalanced sex ratio in our sample of adults captured at the breeding colony. Minimum bill depth and head length, of the seven morphometric characters we measured, successfully assigned the correct gender to 95% of all individuals sampled (n = 37). We provide a canonical classification function of morphological traits that may be used in the field to rapidly differentiate adult females and males of this rare petrel species.

The sub-Antarctic mite Ayersacarus: a new species from mainland New Zealand, and its isotopic ecology (Acari: Mesostigmata: Leptolaelapidae)

Ayersacarus woodi sp. n. (Acari: Leptolaelapidae) is described from Westland petrel (Procellaria westlandica Falla) burrows at Punakaiki, South Island, New Zealand. The genus has previously been reported only from sub-Antarctic islands. The new species is most like A. plumapilus Hunter (type species) but differs from it in females in the size and shape of the epigynal shield; much larger metapodal shields; and a wider than long anal shield with lateral pores. The ecology of the new species was explored using stable isotope (13C/12C; 15N/14N) analysis of females alongside contextual data from the site. From the 13C/12C results, the new species is dependent on marine C from petrels rather than terrestrial photosynthetic C. In terms of trophic level, the isotopic data are consistent with consumption of guano decomposers or their eggs.

Dynamics of Seasonal Movements by a Trans-Pacific Migrant, the Westland Petrel

Abstract. Knowledge of the dynamics of long-distance migrations of pelagic seabirds is limited. Recent advances in tracking technology have yielded detailed, continuous accounts of the movements of individual seabirds over large spatial and temporal scales. We studied the timing of migration and year-round distribution of the Westland Petrel (Procellaria westlandica), listed by the IUCN as vulnerable, with miniature archival light loggers (geolocators) deployed on 10 incubating birds breeding in 2007 at Westland, New Zealand. We retrieved data from eight Westland Petrels, indicating the birds migrated in November directly east ∼7000 km from the coast of New Zealand to South American waters in 6 days (range 4–7), then returned the following April in 10 days (range 8–13). The durations of an individual's outward and return flights and the dates of its outward and return migrations were positively correlated. During their journeys east and west, birds spent on average (±SD) 9.9% (±9.7) and 17.2% (±12.0), res...

Using 137Cs and 210Pb to characterise soil mixing by burrowing petrels: an exploratory study

This exploratory study tested the hypothesis that petrels (Aves: Procellaridae) actively plough the soil of their entire breeding colonies, as implied by their well-known burrowing capabilities but contra-indicated by widespread horizonation in colony soil. Two profiles to lithic contact were excavated within a forested Westland petrel (Procellaria westlandica) colony; one, a ridgeline control without nearby petrel burrows, and the other from a steep slope among petrel burrows. On the ridgeline, 137Cs activities (estimated per volume) steadily decreased with depth as expected. At the burrowed site, a subsurface maximum at 12–16 cm depth indicated a post-1963 burrowing or landslip event. Both 210Pb profiles were successfully modelled (r 2 c. 0.9) using a simple first-order model usually applicable only to undisturbed soils. In this model, mixing is accounted for by radioactive decay and first-order, mm-scale biodiffusion. The results therefore indicated that soil mixing was not dominated by petrel burrowing; rather, petrels confine their burrowing activities to maintenance of their burrows as semi-permanent (decades to centuries) structures. However, further sampling is recommended to confirm this view.

Stable isotopic (δ15N, δ13C) analysis of wood in trees growing in past and present colonies of burrow‐nesting seabirds in New Zealand. I. δ15N in two species of conifer (Podocarpaceae) from a mainland colony of Westland petrels (Procellaria westlandica), Punakaiki, South Island

Marine nitrogen (N) has been traced into terrestrial and freshwater food chains at petrel (Aves: Procellariiformes) colonies on the South Island of New Zealand, but the effects of N or other marine‐derived nutrients on the productivity of mainland forests are unknown. Mean ring widths in matai (Prumnopitys taxifolia; n = 3) and rimu (Dacrydium cupressinum; n = 2) trees growing in a Westland petrel (Procellaria westlandica) colony were 0.9–1.4 mm yr–1, similar to ring widths reported elsewhere. However, series of much wider rings in cores showed that trees in a petrel colony can experience periods of accelerated growth. δ15N values of whole wood were, at 3.2–11.1%, significantly enriched in comparison to other temperate forest trees. The highest δ15N values were at the cambial and pith ends of different cores, so isotopic fractionation during N remobilisation is unlikely to have been significant. The radial extent of 15N enrichment suggests that petrels have bred at the site since at least the mid 18th century.

Demography of Westland Petrels (Procellaria westlandica), 1995–2003

We studied the Westland Petrel (Procellaria westlandica) over 9 years to estimate demographic rates and examine the possible influence of fisheries by-catch and nest predators on the population. Mean annual survival rates of breeders and skipped-breeders averaged 0.965 (s.e. = 0.038) and 0.726 (s.e. = 0.173) respectively. Mean fledging success was 0.62 fledglings per egg laid (s.e. = 0.04, n = 34 nests). The birds studied showed no evidence of elevated mortality at either the adult or nestling stages, which might indicate low fisheries by-catch mortality or few predation threats to population stability or both. With apparent survival rates of breeders being near probability of 1, attempts to manage threats to the population, over and above current levels of management, can do little to elevate these survival rates. However, some management actions such as ameliorating habitat destruction or depredation could benefit non-breeding birds, as well as working to keep survival rates in breeding birds high.

Surface soil chemistry at an alpine procellariid breeding colony in New Zealand, and comparison with a lowland site

Procellariid seabirds occupied colonies on the pre‐human New Zealand mainland from the lowlands to alpine areas, but the effect of geographic environment on soil nutrient cycling has not been investigated. To facilitate qualitative predictions of seabird breeding effects on terrestrial ecology and biogeochemistry, we compared surface soil (0–15 cm) results from a Hutton's shearwater colony at 1230 m with a Westland petrel colony in lowland forest. Soil acidity, total C, total N, total Cd, and Cdexcess (the soil Cd which cannot be accounted for by parent material weathering) concentrations were all lower at the Hutton's shearwater colony despite higher burrow occupancy and density. Lower δ15N values and higher pH imply that guano was less nitrified in the soil before being lost. At both colonies, parent material contributed a large portion of total P and total Cd. Correlations between total N, Pexcessand Cdexcess with total C suggested that guano nutrient retention is driven by soil organic matter. We conclude that seabird colony location affected the cycling of seabird‐derived nutrients in pre‐human New Zealand.

Avian assimilation and dispersal of carbon and nitrogen brought ashore by breeding Westland petrels (Procellaria westlandica): a stable isotope study

AbstractOnly a small proportion of the marine nutrients brought ashore by breeding colonial seabirds is retained in colony soils. However, means by which these marine nutrients can be dispersed to the wider terrestrial ecosystem have rarely been identified. In this study, moulted feathers from Hemiphaga novaeseelandiae (an endemic pigeon; n=9) and Gallirallus australis (an endemic flightless rail; n=3) and from a Procellaria westlandica (Westland petrel) colony were analysed for 13C and 15N enrichment. Potential diet items from both the colony and a control location were also analysed, and their contributions to the diets of H. novaeseelandiae and G. australis calculated. Hemiphaga novaeseelandiae assimilated marine N but not marine C, and showed a wide range in the significance of different diet sources. Food for most H. novaeseelandiae came from within the colony, implying minimal transport of marine nutrients to the wider terrestrial environment. All G. australis food came from within the colony, but 29–39% was from petrel tissue, or invertebrates feeding on petrel material. Thus, both H. novaeseelandiae and G. australis assimilated nutrients brought ashore by P. westlandica, but neither was shown to disperse the nutrients much beyond the petrel colony. However, birds that are now locally extinct may have dispersed marine nutrients more widely. Future research should focus on the consequences of restoring these species to petrel colonies as part of attempts to re‐establish the functioning of pre‐human ecosystems in New Zealand.