David J. Hawke

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

Only 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.

Soil P in a forested seabird colony: inventories, parent material contributions, and N : P stoichiometry

Guano from breeding seabirds provides a large external source of nutrients to the soils of breeding colonies. However, little is known of guano P retention relative to N or the relative importance of guano and soil parent material as P sources. Soil profile N and P inventories (0–0.60 m, n = 4; 0–0.36 m, n = 1) and guano N and P concentrations were measured at a Westland petrel colony, and the parent material contributions of P were calculated using Ca, Al, Fe, Ti, and Zr as reference elements. Median inventories (0–0.60 m) were 1.49 kg N/m2 and 332 × 10–3 kg P/m2, the N result being similar to that from a seabird colony on peat soil where N retention was very low. Calculated parent material contributions were smallest (32–66% of soil P) when based on Ca and largest (47–102% of soil P) when based on Zr. Contributions were similar for Al, Fe, and Ti; Al (41–87% soil P) was selected for subsequent calculations. Regardless of the reference element, parent material therefore contributed a large part of soil P. Phosphorus in excess of parent material supply (Pexcess) was significantly correlated with soil C, implying that guano P is held primarily in organic form. The median soil N : P molar ratios were 9.6 : 1 based on total P and 11.2 : 1 based on Pexcess, compared with ratios for Westland petrel guano of 4.1 : 1 (when birds were consuming fisheries waste) and 16.4 : 1 (when fisheries waste was replaced by fish). The similarity between soil and guano N : P ratios implies that both N and P are lost from soil at similar rates, although volatilisation of N would enrich soil drainage water in P. Calculations using guano deposition rates from the literature yielded P residence times of 4–15 years (Pexcess) and 11–41 years (total P), consistent with a highly dynamic soil system.

Maximum possible age of a petrel breeding colony near Punakaiki (South Island, New Zealand) from radiocarbon and stable isotope analysis of soil

Abstract The lifetime of individual petrel colonies is poorly known. This study used radiocarbon, 13C, and 15N analysis of soil to determine the maximum possible age of a colony presently occupied by Westland petrels. A sample of Ap horizon soil in lithic contact was selected for analysis, as soil least likely to have been redistributed by petrel burrowing. Chemical removal of mobile organic matter decreased δ15N from 14.0‰ (typical of breeding colony soils) to 6.1‰ (within the range of temperate forest soils without sea‐bird breeding). δ13C values changed little, from ‐27.1‰ (untreated soil) to ‐28.4‰ (treated soil), and were typical of forest soil with C3 vegetation and no incorporation of marine C. Duplicate AMS radiocarbon analysis of treated sample yielded a combined conventional radiocarbon age of 864 ± 32 BP, indicating that sea‐bird breeding could not have occurred at the site for more than 740–960 calendar years. Initial colony occupation may have occurred much later than this, and not been continuous. Sea bird species other than Westland petrels may also have used the site.

A possible early muttonbirder's fire on Poutama, a Rakiura titi island, New Zealand

Abstract Muttonbirding for sooty shearwaters (Puffinus griseus) on islands around Rakiura is an ongoing traditional activity of local Maori. There is little archaeological evidence to pinpoint the onset of large‐scale birding, so some researchers have suggested that widespread systematic muttonbirding only began in protohistoric times. We present AMS radiocarbon data from an archaeological fire found 65 cm subsurface on Poutama, an island off Rakiura. Duplicate analyses of charcoal and a single analysis of underlying peat were used to date the fire, constrained by C accumulation calculations and chemical and isotopic analysis. By comparing C:N ratios and C accumulation calculations with literature values, the peat result (176 ± 55 BP) was shown to be invalid because of contamination viabioturbation. The combined charcoal radiocarbon data were consistent with being estimates of a single value (326 ± 42 BP). After calibration, the fire was dated at AD 1470–1660 (95% confidence interval). Carbon‐13 analysis was consistent with charcoal from different individual plants. The C accumulation rate (61–96 g C m–2 yr–1) was at the upper end of literature values, consistent with a high nutrient and well‐oxygenated soil environment. Our results highlight the need for more systematic data collection and experimentation to better assess the time of onset of systematic muttonbirding.

Mobilisation of recalcitrant soil nutrient fractions supports foliar nitrogen to phosphorus homeostasis in a seabird soil

Background and aimsAlthough the nutrient enrichment literature emphasises anthropogenic sources, seabirds deposit large quantities of marine detritus at breeding and roosting sites. Little is known of the chemical fractions and plant availability of seabird soil nutrients and their relationship to nutrient limitation patterns.MethodsNutrients in mineral soil from a breeding colony of burrowing seabirds were progressively depleted by growing radiata pine (Pinus radiata D. Don.) and wheat (Triticum aestivum) separately in small pots over 4–10 months. Soil from destructively sampled pots was analysed using a version of the Hedley fractionation scheme; foliage was analysed for C, N and δ15N using isotope ratio mass spectrometry, and for P using microwave assisted digestion and ICP-OES.ResultsFoliar C:N and δ15N increased with plant mass for both species, but N:P remained constant within plants of each species. As total soil P was progressively depleted, concentrations of bicarbonate-extractable soil P were maintained. This occurred mainly by depletion of non-labile inorganic P forms, thus demonstrating potential mobilisation of all refractory P (as defined by our chemical fractionation method) into plants growing at the seabird site. The increasing foliar δ15N was consistent with the progressive mobilisation of more highly recycled forms of N.ConclusionsWe infer a species-specific stoichiometric homeostasis for N and P in plants grown in seabird soil, facilitated by mobilisation of recalcitrant forms of soil N and P.

Nutrient sources for forest birds captured within an undisturbed petrel colony, and management implications

Abstract Where seabird breeding colonies occupy forested habitats, unusual nutrient links between marine and terrestrial ecosystems can occur. In such circumstances, the dietary characteristics of forest birds inhabiting pristine seabird colonies have rarely been investigated. In this study, carried out in a mixed-species colony of petrels (Procellariiformes), we measured the stable isotopic (δ13C, δ15N) signatures of individual feathers of New Zealand Bellbirds (Meliphagidae: Anthornis melanura melanura; n = 6) and Red-crowned Parakeets (Psittacidae: Cyanoramphus novaezelandiae novaezelandiae; n = 15). The δ15N of Parakeet feathers encompassed a wide range, from +7.1%o to -0.9%. From the high maximum δ15N, relative to global temperate forest foliage, we conclude that some Parakeets were feeding within the petrel colony where they were captured. However, the low minimum δ15N, relative to foliage from the petrel colony, implies that Parakeet isotopic composition could not be fully explained by potential dietary items from the petrel colony. Bellbird δ15N (range +3.4% to +9.6%) was more enriched than that of Parakeets, consistent with their higher trophic level, but also consistent with a dietary intake consisting of items from both within and beyond the petrel colony. Bellbird isotopic ratios were strongly enriched in δ13C, which could be explained only by consumption of invertebrates with marine isotopic enrichment. The marine invertebrates could have been associated with breeding petrels, or have come from the littoral zone near the site of capture. The importance for both species of food sources both inside and outside of petrel colonies implies that petrel colonies offer foraging opportunities for forest birds but that the birds also use non-colony areas. Consequently, petrel colonies are integral parts of the wider terrestrial landscape which they inhabit.

A new epizoic laelapid mite from the New Zealand sand scarab Pericoptus truncatus larvae and its isotopic ecology

Abstract A new genus Mumulaelaps (Mesostigmata: Laelapidae: Hypoaspidini) is proposed to hold large, pale, agile, gregarious mites associated with the larvae of the endemic xylophagous sand scarab Pericoptus. Mumulaelaps ammochostos sp. n. is described and illustrated as its type species from P. truncatus (Fabricius) from Southshore, Christchurch, New Zealand. The new genus bears a novel mix of characters shared with Hypoaspis G. Canestrini, 1884 and Coleolaelaps Berlese, 1914 but differs from both by having, in both sexes, stout terminal spines al1 and pl1 on legs II–IV and bearing long or macrosetae of the dorsal series on femora and genua of legs II–IV. Both sexes have leg IV longest and leg II shortest with III never longer than I. The posterior edge of the sternal shield is deeply concave; the post anal seta is longer than the paranals; the hypostomal seta h3 clearly longer than h1 or h2. Stable isotopic (13C/12C; 15N/14N) analysis showed that the new species is not parasitic, but its trophic association with P. truncatus is unclear. It may feed on the hypopodes of Sancassania (=Caloglyphus) or nematodes associated with P. truncatus.

Isotopic signatures (13C/12C; 15N/14N) of blue penguin burrow soil invertebrates: carbon sources and trophic relationships

Abstract Seabird burrows provide a soil environment for processing discards such as feathers and guano, hence constituting a primary interface between the sea and the land. This study involved collection and culturing of soil invertebrates from three blue penguin (Eudyptula minor) burrows, and examined their 13C/12C and 15N/14N isotopic composition in relation to potential burrow resources (terrestrial plant litter, burrow soil, guano, blue penguin feathers). Two taxa (cerylonid beetles and small tineid moth larvae) had a depleted 13C/12C indicative of a level of dependence on C from terrestrial soil. Tineid moth larvae (Monopis crocicapitella and (or) M. ethelella) substantially increased their 13C/12C enrichment during development, implying increasing dependence on marine C. Remaining taxa, both decomposers and predators, had 13C/12C intermediate between guano and feathers. Larval and emergent fleas had the most enriched 13C/12C, indicative of a greater dependence on feather C and the likelihood of co-processing with guano. Pseudoscorpions and histerid beetles had overlapping isotopic enrichments implying competition for prey, but were spatially separated in burrow soil. With their highly enriched 15N/14N and marine 13C/12C, larvae and protonymphs of the histiostomatid mite Myianoetus antipodus stood alone. Blue penguin burrows therefore support a diverse invertebrate fauna that incorporates terrestrial soil as well as varying proportions of the various blue penguin discards.

Incorporation of the invasive mallow Lavatera arborea into the food web of an active seabird island

This study investigated the role of the invasive mallow Lavatera arborea in the terrestrial ecosystem of a flourishing seabird island in SE New Zealand using natural abundance stable isotope ratios (13C/12C; 15N/14N, reported as δ13C and δ15N). Foliage samples of L. arborea came from transects encompassing three distinct environments (plateau, slope, storm-washed flat) across the island. Samples of potential marine nutrient sources (beach-cast kelp; seabirds using the island) were also collected, to contextualise the L. arborea data. Samples of invertebrate taxa (exotic and indigenous) from multiple ecosystem guilds were hand-collected; a bee, a sap-sucking Homoptera, a litter-feeding tenebrionid beetle, various carrion-feeding flies, a predatory carabid beetle, a salticid spider, and (from a seabird cadaver) Dermestes sp. exuviae. Discarded skins from the gecko Hoplodactylus maculatus were collected from moulting sites. Highly enriched δ15N values showed that L. arborea from all three environments utilised seabird N, even though breeding seabirds were absent from the storm-washed flat. The isotopic signatures of the Homoptera, and the tenebrionid and carabid beetles could be accounted for entirely by food webs based on L. arborea. Bee and salticid spider isotopic signatures could be accounted for by varying contributions from L. arborea. The flies and Dermestes were (as expected) linked to carrion from either the island or the adjacent mainland. In contrast, gecko data indicated direct dependence on seabirds, although the exact relationship was unclear. Our study therefore showed that L. arborea is an integral part of the terrestrial ecosystem of the island across multiple trophic levels from pollinators to top-level predators.

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

Abstract 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 Huttons 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 Huttons 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.