density

Estimating abundance, age structure and sex ratio of a recently discovered New Zealand tusked weta Motuweta riparia (Orthoptera, Anostostomatidae), using mark-recapture analysis

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.

Social and spatial structure and range use by Kaimanawa wild horses (Equus caballus : Equidae)

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.

Density of rabbits (Oryctolagus cuniculus L.) in the Mackenzie Basin, South Island, New Zealand

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 density and diversity in relation to disturbance in agroecosystems in New Zealand, with a comparison to England

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.

Calibration of tunnel tracking rates to estimate relative abundance of ship rats (Rattus rattus) and mice (Mus musculus) in a New Zealand forest

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.

Population-Dynamics and Diet of Rodents on Rangitoto Island, New Zealand, Including the Effect of a 1080 Poison Operation

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.

Indexes of Density of Feral Goats in a Grassland Forest Habitat, Marlborough, New Zealand

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.

Feral Goats on Raoul Island. I. Effect of Control Methods on Their Density, Distribution, and Productivity

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.

Accounting for detectability when estimating avian abundance in an urban area

Urban areas can support significant bird populations, including species of conservation concern, but urban ecologists have been slow to apply detectability-based counting techniques. We compared abundances and relative abundances of eight urban birds, derived using two commonly applied techniques (fixed-radius point and strip sampling) and distance sampling. We evaluated the influence of habitat and two covariates (observer and whether birds were seen or heard) on detectability. Due to built-up structures in urban areas, point counts are appropriate.

Line-transect distance sampling compared with fixed-width strip-transect counts for assessing tomtit (Petroica macrocephala) population trends

Distance sampling and fixed-width strip-transect counts were compared as methods for estimating population trends of the tomtit (Petroica macrocephala) from late September / early October to early November 2004, before and after aerial 1080-poisoning for control of the brushtail possum (Trichosurus vulpecula). Two observers independently recorded the distance and compass bearing to tomtits detected along 36 transect lines in each of two forests (one prefed with non-toxic bait and one not prefed).

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