Brushtail possums (Trichosurus vulpecula) present an ongoing threat to New Zealand’s environment and economy. Research into additional control techniques is vital to ensure that a variety of efficient tools are available to help achieve population suppression. Encapsulated sodium nitrite (NaNO2) has been developed in New Zealand as a new toxin for possum and feral pig (Sus scrofa) control. Its toxic effects at high doses are mediated through the induction of methaemoglobinaemia, a condition in which the carrying capacity of oxygen in red blood cells is reduced.
The application of fensulfothiqn and parathion for the control of invertebrate pasture pests in Canterbury during March, April and May 1970 killed many birds and mammals. Two hundred and thirty-six dead birds were found after a single application of fensulfothion to 123.4 ha, and 158 birds were recovered from 78.5 ha of pasture treated with parathion. The main species killed were white-backed magpie (Cymnorhina tibicen), black-backed gull (Larus dominicanus) and harrier hawk (Circus approximans).
Brodifacoum is a second-generation anticoagulant used for rodent control in New Zealand. Concerns about the poisoning of non-target species have resulted in restrictions being imposed on the mainland. It is, however, still commonly employed on offshore islands. Previous research investigating the poisoning risks of brodifacoum has generally focused on birds eating brodifacoum bait (primary poisoning) or through depredation of live rodents or carrion containing brodifacoum residues (secondary poisoning).
Lesser short-tailed bats (Mystacina tuberculata) feed on arthropod taxa known to consume 1080 baits. Thus, they may be vulnerable to secondary poisoning after control operations for brushtail possum (Trichosurus vulpecula) using aerially broadcast 1080 baits. Short-tailed bat mortality was monitored during 11 days after 1080 baits were broadcast over their winter foraging area. Monitoring involved catching a sample of 269 bats as they arrived at a roost after foraging, then holding them in captivity for 48 hours.
The diet of radio-tagged moreporks (Ninox novaeseelandiae) was studied at Pureora Forest from May to December 1997. An examination of 187 pellets yielded 1226 prey items. Approximately 99% of the diet was invertebrates; the commonest items being beetles (48.6%), stick insects (25.6%) and weta (11.8%). Vertebrate prey included silvereye (Zosterops lateralis) and rodents in small numbers. The diet varied significantly from month to month.
A single five night pulse of sodium monofluroacetate (0.15% 1080) applied in bait stations at two different spacing intervals, 100 and 200 m, along forestry roads in New Zealand beech forest, killed all four of the resident radio-tagged stoats (Mustela erminea) and all three of the resident radio- tagged wild house cats (Felis catus) by secondary poisoning. Gut contents of predators indicated that house mice (Mus musculus), ship rats (Rattus rattus) and bushtail possums (Trichosurus vulpecula) were important sources of the toxin.
We monitored 16 radio-tagged moreporks (Ninox novaeseelandiae) on Mokoia Island after a brodifacoum poison drop to eradicate mice (Mus musculus), normally included in the owls' diet. All 16 moreporks were alive after 13 days. One bird was found dead on day 22, and corpses of two radio-tagged birds were located on day 51. The bird found on day 22 contained 0.97 mg kg(-1) of brodifacoum in its liver. The other two carcasses were not analysed, but they probably died as a result of brodifacoum poisoning. Thus, three out of 14 birds died (21% mortality).
Aerial poisoning using Talon(R) 7-20 baits (active ingredient 20 ppm brodifacoum) was carried out on Motuihe Island, Hauraki Gulf, during the winter of 1997. The operation aimed to eradicate Norway rats (Rattus norvegicus) and house mice (iMus musculus) and to reduce rabbit (Oryctolagus cuniculus) numbers significantly. We studied the diet of feral house cats (Felis earns) before the operation, then monitored the impact of the operation on them to determine whether secondary brodifacoum poisoning caused a reduction in their numbers.
In Britain, the use of "second-generation'' rodenticides has become widespread on agricultural premises. The high toxicity and relatively long half-lives of these compounds has raised concerns over potential secondary exposure and poisoning of non-target predators. Over the last 15 years, exposure has been extensively documented in the barn owl Tyto alba but relatively little is known about mammalian terrestrial predators.
Stoats were monitored by three methods through an aerial 1080 poisoning operation at Waimanoa, Pureora Forest in August 1997. Tracking rates and number of live captures were used as indices of abundance, and radio-transmitters were used to follow individual animals. All 13 stoats with radio-transmitters within the poisoned area died between 2-18 days after the operation. No mustelids were tracked or live-trapped after the operation for three months. Of the radio-tracked stoats that died, rat remains occurred in 67%, passerine birds in 17%, cave weta in 17% and possum in 8%.