survival

Managed pine plantations now constitute a large portion of mainland New Zealand. Despite many native birds inhabiting these exotic habitats, their value for biodiversity conservation is unclear. Although numerous studies have quantified densities of native bird species in pine plantations, it is unknown whether these individuals constitute self-sustaining populations. Here we address this question for North Island robins (Petroica longipes) in a Pinus radiata plantation in the central North Island.

Seedlings of five native tussock species grown in the glasshouse on mountain subsoil showed outstanding responses to nitrogen and phosphorus fertiliser in combination. The most vigorous species was silver tussock but this produced less dry matter than an introduced grass, Yorkshire fog, grown on the same soil. Tussocks in general responded positively to applications of magnesium and potassium but growth was depressed by lime.

The mountain stone weta Hemideina maori, a tree weta, is a cold-adapted New Zealand insect that shows increasing body size with increasing altitude and decreasing temperature. This study modelled the monthly survival probability of adult weta at three sites (high, medium and low altitude) in the Rock and Pillar Range, Otago. Survival was predicted to be lowest at the low elevation site where weta are at the lower limit of their current altitudinal range. A total of 504 adult weta were marked and released at all three sites between November 1999 and May 2002.

Although reproductive and behavioural studies have been conducted on captive tree weta, there have been very few ecological field studies of any of the weta species involving free-ranging, marked individuals. The mountain stone weta (Hemideina maori) is a tree weta that lives on rock tors in the alpine region of the South Island of New Zealand. Over three seasons each of 480 adults and 789 juveniles was individually marked on four large and 14 small tors to gather baseline information on aspects of H. maori’s life cycle and life history.

To measure the costs and benefits of an aerial 1080 possum control operation to kereru and kaka in Whirinaki Forest Park, individuals of both species were radio-tagged from October 1998 to June 2002. We monitored birds in one treatment and one non-treatment study area to compare toxin-related mortality, nesting success and survival. The poison operation involved the spreading of non-toxic carrot baits on 1 May 2000, and the toxic baits on 17/18 May 2000.

Nest success, the proportion of clutches resulting in one or more fledglings, is a key indicator for assessing the effect of management on bird populations. However, the figures reported for New Zealand populations are usually "apparent nest success", the number of successful nests divided by the total number found. Apparent nest success invariably overestimates the true success rate, and the degree of bias depends on the population and monitoring regime. Consequently, apparent nest success rates cannot be reliably compared.

Hihi (Notiomystis cincta) were reintroduced to Mokoia Island, Lake Rotorua, New Zealand, in September 1994, and two years later there was an aerial drop of brodifacoum cereal pellets aimed to eradicate mice (Mus musculus). Using Program MARK, we analyzed data from resighting surveys to assess whether hihi had lower than normal survival in the 6-week interval following the drop. The resighting data were collected on a regular basis over a 3-year period, from 1994-97, allowing us to control for yearly and seasonal variation in resighting and survival probabilities.

Several recent studies have used "roll calls"—searches for individually-marked birds—to assess impacts of aerial poison operations on non-target species. Roll calls have advantages over methods such as 5-minute bird counts, call counts, and dead body counts, but roll calls are based on the assumption that detection rates are 100%, or that detection rates are constant over time and space. They also require more than one group of birds, at a poisoned and unpoisoned site for example, for valid statistical comparisons.

Mountain stone weta (Hemideina maori) on the Rock and Pillar Range in the South Island, New Zealand, are found primarily in cavities under flat rocks on isolated outcrops or 'tors'. We marked 66 adult weta on one tor and 30 adults on an adjacent tor and recorded their location during the summer and for the following three years to obtain baseline data on survival, longevity, dispersal, and movement within tors. It was not uncommon for adult weta to live for two to three years. Most marked weta were resighted at least once, usually under the same rock.

To assess the effect of possum browse on plant growth, an index of the amount of foliage on about 50 trees of Fuchsia excorticata and the number of trees that died or were completely defoliated was measured at five sites in South Westland over 5 years. This index was compared to possum density indices taken at each site each year. At one site, possums were reduced from a high density about 6 months before the final measurement. The degree of defoliation of fuchsia was significantly related to the density of possums at each site.