Assessment of pyroligneous acid as a pest bird deterrent in a New Zealand pest-exclusion fenced sanctuary

The creation of predator-free sanctuaries, sometimes enclosed by predator exclusion fences, is a common conservation and restoration tool in New Zealand. One such site, the Rotopiko wetland complex, in Waikato, is challenged with large flocks of non-native house sparrows (Passer domesticus) and common starlings (Sturnus vulgaris)—an estimated 500 000 birds—that roost within the predator exclusion fence, with the potential to alter nutrient regimes and plant community composition. Here we investigated the use of pyroligneous acid (wood vinegar) as a deterrent to roosting birds. The relative abundance of guano from roosting birds was quantified using guano plates in two equivalent patches of native forest, representing treatment and control sites, before and after the application of pyroligneous acid. In 2021, we found that guano abundance was 10% lower at the treatment site than at the control site after the application of pyroligneous acid (tested over 31 days). In 2022, guano abundance was 15% lower during the first 10 days of application. Our findings suggest that pyroligneous acid has promise as an additional option in the bird pest management toolbox. However, further research is needed to test its efficacy in various contexts, investigate relative impacts on different bird species, and develop application methods that increase the exposure of roosting birds.