The effect of aerially applied 1080 on the nesting success and survival of kākā

Abstract

: Kākā ( Nestor meridionalis ) are vulnerable to predation by stoats ( Mustela erminea ) and possums ( Trichosurus vulpecula ), particularly when nesting. Without predator control kākā populations decline. Control of stoats and possums both by trapping and aerial application of the poison 1080 leads to increased kākā nesting success. In recent years, many 1080 poison operations have been undertaken to control ship rat ( Rattus rattus ) and stoat plagues that occur after beech mast. Kākā do not breed every year but breed in anticipation of heavy fruiting. They do not usually breed during the spring and summers following beech mast when 1080 operations are often undertaken to control rat and stoat irruptions. Using radio-tags we measured the nesting success and survival of kākā for six years in South Westland during which there were beech (Nothofagaceae) and rimu ( Dacrydium cupressinum ) masts, stoat and rodent plagues, five 1080 operations, and four seasons in which kākā bred. We then simulated varying timings and frequencies of masting and 1080 use to explore the impact of masting and predator control on kākā population growth. In the absence of pest control simulated kākā populations declined. Aerial 1080 applied a year before or just before kākā breeding resulted in increased nesting success, but 1080 applied more than two years before kākā breeding had no impact. Aerially applied 1080 also increased adult kākā survivorship for at least 18 months. Annual 1080 operations or 1080 operations at intervals less than or equal to the time it takes stoat populations to recover resulted in the most rapid simulated kākā population growth. 1080 operations in (1) kākā breeding years, (2) when following mast, and (3) during rodent and stoat plagues each resulted in progressively smaller kākā population growth rates.