The effects of single aerial 1080 possum-control operations on common forest birds in the South Island, New Zealand

We used a long-term replicated before-after control-impact (BACI) sampling design to monitor the effect of aerial 1080 possum-control operations on common forest bird populations. Paired treatment and non- treatment sites in the Rolleston Range (East Coast, South Island) and Alexander Range (West Coast, South Island) were monitored once before 1080 treatment during winter 2012 and for three successive summers afterwards. Mammals (possums Trichosurus vulpecula, rats Rattus spp. and mice Mus musculus) were monitored with chew cards, and forest birds with ve-minute counts. Possums decreased to negligible levels in treatment sites, but increased over time in non-treatment sites. Rats were only present at the West Coast sites, where there was a signi cant, but short-lived, decrease post-1080. Mouse abundance showed almost no effects post-1080, but increased at the East Coast sites after a beech (Nothofagus spp.) mast seeding event. No common native bird species showed short-term negative effects post-1080. Three species – tomtit (Petroica macrocephala), silvereye (Zosterops lateralis), grey warbler (Gerygone igata) – increased signi cantly. Longer-term effects on birds were nearly all neutral or positive, including bellbirds which increased three-fold in treatment areas. In non- treatment areas, higher possum densities were correlated with subsequent decreases in bird counts (averaged across all species). Overall, the one-off aerial 1080 treatment had conservation bene ts.