Nelson Lakes National Park Research Articles

Individual specialists within a generalist niche: variable diet of stoats and implications for conservation

Conservation programmes aiming to suppress or remove invasive small mammal populations that threaten endemic fauna assume that eliminating an individual predator has the same effect as eliminating a conspecific in terms of decreasing risk to the prey species. However, marked between-individual variation in prey take could, at times, lead to uneven predation pressure. Such variation in the diets of introduced predators has long been hypothesised in New Zealand, suggesting that some observed rates of predation are not typical of the prey population as a whole. We used stable isotope analysis to estimate the isotopic dietary niches of stoats Mustela erminea (n = 51) caught in three New Zealand National Parks. We modelled δ13C and δ15N ratios from five tissue types to estimate the isotopic niche for each individual stoat, and for each population. The isotopic niche used by the population of stoats in Nelson Lakes National Park was substantially larger (5.3 ‰2) than for those at either Mt Aspiring National Park (3.1 ‰2) or Fiordland National Park (2.8 ‰2). Despite this, a measure of individual specialisation (proportional niche use) in stoats at Nelson Lakes National Park (0.4 ± 0.3) was similar to the other two sites. Collectively these data suggest a comparable degree of individual specialisation even within a more generalist population niche. This variability in the range of prey items taken by small carnivores, between populations and individuals of the same species, has consequences for how we design and monitor small mammal control programmes; for example, the threatened species outcomes observed in one area or time period may not be applicable to another.

Is Avian Malaria Playing a Role in Native Bird Declines in New Zealand? Testing Hypotheses along an Elevational Gradient.

The mosquito-borne disease avian malaria (Plasmodium spp.) has impacted both captive populations and wild individuals of native New Zealand bird species. However, whether or not it is a cause of concern to their wild populations is still unclear. In Hawaii, the disease has been a major factor in the population declines of some native forest bird species, often limiting their elevational distribution due to an inverse relationship between force of infection and elevation. While studies have investigated latitudinal patterns of infection in New Zealand, elevational patterns are unexplored. To address this, a survey was conducted in Nelson Lakes National Park, a site experiencing native bird declines in which disease has been suggested as playing a role, to investigate whether there is a similar inverse relationship in New Zealand. Results from blood samples (n = 436) collected over three seasons across a broad elevational range (650–1400 m) support there being such a relationship. In addition, an overall higher prevalence in non-native (14.1%) versus native birds (1.7%) may indicate differential impacts on these two groups, while particularly high prevalence in non-native Turdus spp. supports previous suggestions that they are key reservoir hosts for the disease. Overall, these findings add weight to the hypothesis that avian malaria is playing a role in ongoing declines of native New Zealand birds.

Effective distances of wasp (Vespula vulgaris) poisoning using clustered bait stations in beech forest

Poison baiting from fixed bait stations is currently the most effective method to reduce the ecological impacts of invasive Vespula vulgaris wasps in New Zealand. Maintaining extensive bait lines or grids and later removal of unused baits within forest habitats is, however, difficult and time-consuming. To improve cost- effectiveness and to make use of wasps' ability to forage at long distances from the nest, we tested the efficacy of using clusters of bait stations. We set up three clusters around Lake Rotoiti within Nelson Lakes National Park, each containing eight stations baited with Xtinguish TM (active ingredient 0.1% fipronil) for 3-4 days in early February, 2010 and recorded the traffic rates of 144 V. vulgaris nests, at varying distances from bait clusters, before and after treatment. The distance from a bait station cluster significantly affected the change in traffic rates, with a GLM model predicting an 80% reduction in average colony size within 113 m of a cluster, and a 50% reduction within 250 m but no reduction at 470 m. The efficacy of the poison baiting was affected by initial colony size - large colonies had greater reductions in traffic than small colonies. Nests up to 150 m higher in elevation than the clusters were as likely to be destroyed as those at the same elevation as the clusters. While overall this baiting strategy did not produce the 80-90% average traffic reductions achieved by more intensive grid baiting systems, it suggests that spacing grouped bait stations approximately 250 m apart has the potential to reduce wasp densities to below an ecologically damaging level with considerably less effort.

Exceptional visual clarity and optical purity in a sub‐alpine lake

Blue Lake, a remote sub‐alpine lake, in Nelson Lakes National Park, New Zealand, has exceptional optical purity. Horizontal sighting range (‘visibility’) on six visits approached 80 m, the theoretical limit based on accepted light‐attenuation coefficients for pure water, making Blue Lake the most visually clear freshwater yet reported. Blue Lake is characterized by blue‐violet hues seen only in the clearest natural waters. Light penetration is as expected for pure water, except in the ultraviolet to blue spectrum where light‐attenuation is increased slightly by very low (‘oceanic’) concentrations of colored dissolved organic matter. Particulate concentrations are extremely low, comparable to those in the Southeast Pacific Gyre, and the lake is hyper (ultra) oligotrophic (Chlorophyll a concentrations ∼ 0.014 mg m−3). Continuous monitoring of beam attenuation (532 nm) over 18 months demonstrated consistently high visual clarity, except for short‐lived episodes following turbid inflows from ephemeral streams. The dominant inflow to Blue Lake comes from springs emerging from the face of landslide debris separating the lake from nearby glacial Lake Constance. The optical purity of Blue Lake apparently reflects efficient removal of particles and dissolved organic matter during groundwater flow from Lake Constance to these springs. Blue Lake may be valuable in aquatic optics research for testing optical instruments and models.

Declines in common, widespread native birds in a mature temperate forest

Common, widespread species are important for ecosystem structure and function. Although such species have declined in some parts of the world, for most ecosystems there is a lack of information about changes in the population status of common species. We studied the abundance of common, widespread forest birds in Nelson Lakes National Park, New Zealand using standardised 5-min bird counts, carried out over a 30-year time span. There was a significant change in the bird community structure during this period. Five native species (bellbird, rifleman, grey warbler, New Zealand tomtit and tui) declined in abundance during the 30 years. All of these declined in abundance at low but not high altitudes, and the decline was substantial for all but New Zealand tomtit and tui. Three other native species increased in abundance (silvereye, yellow-crowned parakeet and New Zealand robin). There was no change in the abundance of introduced blackbirds. We suggest that invasive alien species are the most likely cause of the ongoing declines in common native species. A peak in brushtail possum abundance and the arrival of a new species of Vespula wasp were two large changes in Nelson Lakes forests that occurred during this study. Both are likely to have added to the ongoing impacts of predation by introduced rats and stoats. We suggest that it is necessary to actively manage introduced species in order to maintain populations of widespread, common native bird species in New Zealand.

Residues of brodifacoum and other anticoagulant pesticides in target and non‐target species, Nelson Lakes National Park, New Zealand

Cereal‐based bait containing 20 ppm brodifacoum was used in bait stations continuously from December 1997 to August 2000 in the Rotoiti Nature Recovery Project area, for controlling brushtail possum (Trichosurus vulpecula), ship rat (Rattus rattus), and house mouse (Mus musculus) populations. Concurrently (and before and after), baits containing brodifacoum, bromadiolone, flocoumafen, coumatetralyl, or warfarin were also used in St Arnaud village and on farms immediately adjacent to the project area. Brodifacoum residues were detected in the livers of 234 mammals from eight species, and two birds from two species captured alive, and a further seven birds from five species found dead in the project area (cause of death unknown). The highest concentration of brodifacoum residues in mammalian livers was recorded during the period brodifacoum was used in the project area. However, residues were present in the livers of some individuals at least 24 months after brodifacoum use in the project area stopped. These residues may have persisted in animals surviving brodifacoum use in the project area, and/or been transported into the area by animals moving to and from the adjacent village and farms, where brodifacoum use continued. Residues of flocoumafen, coumatetralyl, or warfarin, used only in the village and on farms, were also detected in the livers of animals captured up to at least 8 km from the nearest source. The results concur with other studies cautioning against indiscriminate or prolonged use of persistent anticoagulants for vertebrate pest control. However, the risks from such pesticides must be balanced against the demonstrable benefits of reducing pest abundance.

Two new species of Pseudocoremia and reinstatement of P. pergrata as species (Lepidoptera: Geometridae: Ennominae)

Two new species of Pseudocoremia (tribe Boarmiini) are described, Pseudocoremia amaculata sp. nov. from St Arnaud, Nelson Lakes National Park, and Pseudocoremia dugdalei sp. nov. from the Waitakere Range, Auckland. It is also determined that P. pergrata, which has been synomynised with P. insignita, should be reassigned species status.

Comparison of the quality of red and silver beech (Nothofagus) seeds in Nelson Lakes National Park, New Zealand

Red (Nothofagus fusca) and silver (N. menziesii) beech seeds were collected during 1995 using 100 seedfall trays. This was a mast year for red beech (74% viability) but only a partial mast year for silver beech (28% viability). Differences between triquetrous and flat seeds are probably confined to shape, since weight and percent germination were the same for both types of red beech seeds. There was a trade‐off between the number of seeds and seed weight for red beech, but little evidence of one for silver beech. The weight, viability, germination, and NPK content of red beech seeds were greater than for silver beech. Both species had a similar energy content per gram of seeds, but the larger red beech seeds contained three times more energy per seed (180 kJ) than silver beech (60 kJ). Greater reserves of energy and nutrients might produce more vigorous seedlings, but make seed predators prefer red beech seeds.

Diet of longfinned eels,Anguilla dieffenbachii, in Lake Rotoiti, Nelson Lakes, New Zealand

Abstract The diet of 72 longfinned eels, Anguilla dieffenbachii, from Lake Rotoiti, Nelson Lakes National Park, New Zealand, was numerically dominated by snails, especially Lymnaea. Larvae of the dragonfly, Procordulia grayi, were extensively eaten as they migrated towards the shore for emergence. By weight, the most important food was fish, with upland bullies, Gobiomorphus breviceps, most important for eels 700 mm.

Longevity of longfinned eels Anguilla dieffenbachii in a New Zealand high country lake

AbstractA sample of 146 longfinned eels (Anguilla dieffenbachii), ranging in length from 231–1203 mm, was collected from Lake Rotoiti, Nelson Lakes National Park, New Zealand. Otoliths (n= 114) of eels were difficult to read, mainly due to the considerable age (maximum age 106 years). Growth rate was slow and linear, averaging 9 mm. year−1. These are the slowest growth rate and maximum age from any study of Anguilla spp. to date. Lakes within National Parks provide the largest commercially unfished waters within New Zealand and hence provide reserve breeding stocks of longfinned eels; however, the average generation time of 93 years for female eels from Lake Rotoiti implies that stock management should be conservative.

Seasonality of crane flies (Diptera: Tipulidae) in South Island beech forest in relation to the abundance ofVespulawasps (Hymenoptera: Vespidae)

Crane flies (Tipulidae) are common in the diet of native insectivores and introduced Vespula wasps. The seasonality of adult crane fly species was determined by Malaise trapping so that species potentially vulnerable to an impact from high wasp numbers could be identified as possible indicator species for analyzing the wider impacts of wasps in beech forest (Nothofagus spp.) ecosystems. Four sites in beech forest at Lake Rotoroa, Nelson Lakes National Park, were sampled over 2.5 years. The seasonality of 20 species of larger Tipulidae were plotted against three broad seasonal levels of wasp abundance identified from Malaise trap catches. Eleven species shared at least 40% of their flight period with high wasp numbers, with three of these restricted almost entirely to the period of high wasp abundance. These species may be the most vulnerable to an impact from wasp predation.

Lichens of Nelson Lakes National Park, New Zealand

Abstract An annotated list of 260 lichen taxa from 82 genera giving habitat information is recorded from several localities in Nelson Lakes National Park, New Zealand. All records are supported by herbarium specimens, with the following taxa being new to the New Zealand flora; Arthrorhaphis citrinella, Calicium viride, Clzaenotlzeca clzrysoceplzala, Everniastrum sorocheilum Hypotrachyna rockii, H. thysanota, Lecidea scalaris, Menegazzia enteroxantha, Pseudocyphellaria ardesiaca, P. berberina, P. hamata, P. hamataoides, P. hirsutula, P. neglecta.

Some bryopbytes of Nelson Lakes National Park, New Zealand

Abstract 152 mosses and c. 99 hepatics are recorded for Nelson Lakes National Park, together with some ecological information. Almost an records are supported by herbarium specimens.

Recent pollen spectra from three localities in the South Island, New Zealand

Summary Surface samples collected at different altitudes and in different plant communities in Westland National Park, the Craigieburn Range (Central Canterbury), and the Nelson Lakes National Park district were studied as a first contribution to knowledge of pollen dispersal from indigenous vegetation in New Zealand. The results emphasise the difference in pollen dispersal between wind-and insect-pollinated plants—differences which are important when interpreting Post-glacial pollen diagrams.