density

House mice (Mus musculus) are an invasive species on Auckland Island in the New Zealand subantarctic and planning for their eradication is underway. Mast seeding events cause rodent populations to irrupt, though little is known about this phenomenon in snow tussock grass (Chionochloa spp.) systems on Southern Ocean islands. The aim of this study was to understand population fluctuations of mouse abundance on Auckland Island for the 2 years following a mast event, and with which tools to monitor abundance, to inform planning of bait application for eradication.

Invasive mammalian pests threaten biodiversity globally across a diverse range of habitats. The unique combination of resource subsidies and disturbance in cities can provide favourable conditions for invasion. Recent interest in urban biodiversity enhancement has increased the demand for effective urban pest control, but efforts are often hampered by a lack of understanding of the ecology of urban invasive mammals.

Estimates of abundance, age structure and sex ratio are essential for monitoring the status of populations. We report the first attempt to reliably estimate these parameters in a population of the recently discovered Raukumara tusked weta (Motuweta riparia), which is found almost entirely near streams. On two occasions we searched a 211-m section of creek for 4–5 successive nights and individually marked all weta. We estimated abundance of adults and juveniles using closed-population mark-recapture analysis.

We measured horse density, social structure, habitat use, home ranges and altitudinal micro-climates in the south-western Kaimanawa ranges east of Waiouru, New Zealand. Horse density in the Auahitotara ecological sector averaged 3.6 horses.per km² and ranged from 0.9 to 5.2 horses.per km² within different zones.

The density of rabbits (Oryctolagus cuniculus) in the modified tussock grasslands of the Mackenzie Basin, South Island, New Zealand, in August-September 1991 was determined within 26 I-ha quadrats spread over 1000 ha. The area was poisoned with 1080- carrot baits and dead and live rabbits counted. The overall kill rate was 93%. Wide variability in rabbit densities amongst the quadrats was correlated with burrow density, but vegetation was not a significant predictor of rabbit numbers. High density quadrats were not all spatially clumped together.

Spider assemblages were sampled by quantitative sampling in pasture and arable habitats under different management regimes in the lower North Island of New Zealand. Density and species diversity increased with decreasing frequency and/or intensity of disturbance from two species and 1.8 individuals per m in wheat to 16 species and 130 indiv. per m in an abandoned, ungrazed pasture. The spider fauna was dominated by introduced species of money spiders (Linyphiidae). The most abundant species, Lepthyphantes tenuis, is also the most abundant one in British cultivated habitats.

Ship rat (Rattus rattus) and mouse (Mus musculus) density and habitat use were estimated by snap trapping and tracking tunnels at Kaharoa in central North Island, New Zealand. Eighty-one ship rats were caught in an effective trapping area of 12.4 ha. Extinction trapping gave an estimated density of 6.7 rats ha(-1) (6.5-7.8 rats ha(-1), 95% confidence intervals). A linear relationship existed between ship rat trapping and tracking rates. Estimating the density of mice was impossible because trapping rates increased rather than decreased during the experiment.

The objective of this study was to quantify the population dynamics, morphological characteristics, and diet of rodents on Rangitoto Island (Hauraki Gulf, New Zealand) to provide information for the future development of an eradication strategy. An aerial 1080 operation to eradicate possums and wallabies was carried out two months after the study began. The effects of this operation on rodent population dynamics are discussed. Both ship rats (Rattus rattus) and mice (Mus musculus) were trapped on Rangitoto Island over a 15 month period.

Hourly kill-rates and encounter-rates for hunters of feral goats (Capra hircus) provided linear indices of goat population size in a 638 ha area of forest and grasslands in Marlborough. The goat population of about 108 animals was reduced to near zero in 105 hours of hunting effort on 11 days at a cost of about $8.20 ha-1. However, goats from the surrounding areas soon recolonised the study area as 19 were shot in 21 hr and 14 in 24 hr 10 and 13 months after the study, respectively.

Goats were liberated on Raoul Island early in the 19th century. Attempts to eliminate the goats commenced in 1937 and have accounted for at least 15 000 animals. Since 1972, when annual hunting expeditions began, both the number of goats and the area over which they range have steadily declined and the herd is now almost extinct. Despite these changes, the mean group size of goats in 1981-83 remained the same at 3.19, 2.74 and 3.24 respectively. On average, 19% of goats escaped each encounter with the hunters.