Responses to pest control in Nelson beech forests.

Being responsible for some of the greatest losses to native biodiversity in New Zealand, brushtail possums (Trichosurus vulpecula), stoats (Mustela erminea) and ship rats (Rattus rattus) are the main targets of predator control. The common methods used to control these species include trapping, poison bait stations, and aerially applied sodium fluoroacetate (1080). In New Zealand beech (Nothofagus spp.) forests, the outcome of predator control operations can be difficult to predict due to species interactions, variation in beech seedfall, and altitude. The objective of my study was to determine the effect of different pest control methods (trapping, and poisoning with diphacinone, pindone or 1080, both ground based and aerial) on ship rat and common forest bird populations, particularly how these effects are influenced by altitudinal gradients and beech masting events. This study used long-term tracking tunnel and five-minute bird count (5MBC) data from areas of beech forest at six treatment and one non-treatment sites in Kahurangi and Nelson Lakes National Parks, South Island, New Zealand. The monitoring data were collected at a range of altitudes and time spans over the course of 14 years (2002-2015), spanning a range in beech seedfall levels including several high-seed years, and an altitudinal range of 600-1450 m a.s.l. The only pest control method analysed here that effectively reduced ship rat abundance was 1080 application. The efficacy of 1080 was not affected by beech seedfall levels but was reduced with altitude since ship rat abundance is greatly reduced above 1000 m a.s.l. The 12 most common bird species detected across all sites included four introduced and eight native species. Most native bird species showed significant declines in response to increased ship rat abundance, and the effect of this was reduced with altitude, indicating that high altitude is a refuge for native birds to escape predation. This study also found evidence for mesopredator release of ship rats following stoat control, and for competition between native and introduced bird species; however both of these findings require further study. Analysis of the long-term data sets confirmed some findings from previous studies but found contrary results to others, which indicated important avenues for future research. This study also highlights the importance of long-term data sets and applying pest control treatments in a standardized way that allows us to optimize methods to manage introduced species for native species conservation