nest predation

We identified nest predators of two European thrush and three European finch species in the central North Island, New Zealand, using artificial clay eggs in active natural nests. The acceptance of the artificial egg by females was 75%, with low rates of female egg ejection (7%) or desertion (7%). Due to high predation rates we could not confirm the acceptance of six (11%) artificial eggs before predation occurred. Of the 57 nests that received an artificial egg 30 were preyed upon.

The theory of population regulation predicts that threatened species are safest at high population numbers, partly because density-dependent compensatory mechanisms counteract unpredictable disturbances. We illustrate this principle using data from the endemic kokako (Callaeas cinerea wilsoni) populations in the North Island, New Zealand. First we calculate the fledging rate per female (production) necessary to stabilise the population and thereby the residual numbers of nest predators, namely ship rats and possums, which have to be achieved to reach this production.

We have been studying the social behaviour and ecology of pukeko (Porphyrio porphyrio) for over five years at a study site in the lower Taieri River, Otago New Zealand. After an application of rabbit poison in 1995 and the illegal release of rabbit haemorrhagic disease (RHD) in 1997, there was strong anecdotal evidence that rabbit (Oryctolagus cuniculus) abundance on and around our study site had been substantially reduced.

Anticoagulant poisons were laid within native forest at Wenderholm Regional Park (near Auckland) to reduce rat numbers during the summer months. Snap trapping indices and an artificial nest experiment confirmed the high potential for rat interference in unpoisoned forest patches outside Wenderholm, compared with the near-zero potential at Wenderholm. Over two breeding seasons, 70 New Zealand pigeon (Hemiphaga novaeseelandiae) nests were located and monitored.

A 55 ha remnant of coastal native forest at Wenderholm Regional Park (near Auckland) was selected as the site for a pilot experiment to test if rat control could yield measurable benefits in increased productivity of New Zealand pigeons. Talon 50WB poison baits were used to reduce rat numbers over the summer of 1992-93. Pigeon breeding success was significantly higher (5 fledglings from 11 nests) than in preceding summers without rat control (no fledglings from 27 nests).

Age and structure of local vegetation (habitat complexity) are commonly assumed to be indicators of habitat quality for breeding birds, but for many species these relationships are poorly understood. The hihi (stitchbird Notiomystis cincta),an endangered New Zealand cavity-nesting passerine that only survives on mammalian predator-free islands or within fenced areas, has been the focus of intensive conservation management and research. Between 1992 and 2004 we examined the fledging success of 347 nests from four island populations.

Artificial nests are frequently used to assess factors affecting survival of natural bird nests. We tested the potential for artificial nests to be used in a novel application, the prediction of nest predation rates at potential reintroduction sites where exotic predators are being controlled. We collected artificial nest data from nine sites with different predator control regimes around the North Island of New Zealand, and compared the nest survival rates with those of North Island robin (Petroica longipes) nests at the same sites.

Investigations of nest predation are often limited by the researchers’ inability to identify nest predators accurately. I tested a chemical bait marker, Rhodamine B (RB), as an indicator of egg predation at artificial ground nests. In a pen trial, the presence of characteristic fluorescent bands in one or more facial vibrissae from all treatment animals confirmed the suitability of RB as a bait marker in the introduced European hedgehog (Erinaceus europaeus).