Assessing bird predation on New Zealand’s lizard fauna using lizard-mimicking replicas

Abstract

<p>Wildlife management is fraught with challenges due to the complexities of community ecology. Interventions aimed at restoring ecosystems, or managing species, can have unintended negative outcomes for target species. The effect of avian predation on native lizard fauna in New Zealand is not clearly understood, despite birds being regarded as top predators within mammal-free ecosystems. At least thirty-one species of bird have been recorded preying on native lizards, but few studies have directly addressed avian predation on lizards, with the majority of evidence sourced from published anecdotes. New Zealand’s herpetofauna are already vulnerable due to range contractions resulting from mammalian predation and habitat loss, with 87% of New Zealand lizard species considered ‘At Risk’ or ‘Threatened’. Understanding the risks posed to lizards will help to inform successful management of vulnerable populations. I used lizard-mimicking replicas to identify and assess predation rates exerted by bird species on lizard populations within the Wellington region of New Zealand. I examined the use of lizard replicas as a tool to quantify predation by examining how birds interacted with replicas and comparing attack rates with novel items simultaneously placed in the field. I determined which bird species were preying on replicas, the extent of such predation, and whether site vegetation or daily weather influenced the probability of avian attack on replicas. Although attack frequency did not differ between novel items and lizard replicas, birds exhibited a realistic predatory response by preferentially attacking the head of lizard replicas. Interactions by birds with lizard-mimicking replicas cannot be confirmed as true predation attempts, but lizard replicas can nevertheless be used to quantify predation pressures exerted on lizard populations by opportunistic bird species. Seven ground-foraging bird species were found to attack lizard replicas. Two species, the pūkeko (Porphyrio melanotus melanotus) and southern black-backed gull (Larus dominicanus dominicanus), were identified as high impact species. The average predation risk experienced by lizard replicas varied greatly across environments, with 0 – 25% of replicas attacked daily at sites. Canopy cover and daily rainfall were not significant predictors, but potentially decreased the likelihood of replica attack. Predation risk varied for lizard replicas as a result of differing assemblages of bird predators at sites, and the presence and foraging behaviour of specific predatory birds. Predation by birds is likely to be an issue where predation pressure is high, or lizard populations are small, range restricted, or recovering from the presence of mammalian predators. When managing vulnerable lizard populations, managers should take into account the threats posed by avian predators so that lizard communities can recover successfully following the same trajectory as native birds.</p>