Can small-scale predator control influence mallard duck (Anas platyrhynchos) nest survival? An experiment with artificial nests in Southland, New Zealand

Artificial mallard (Anas platyrhynchos) nests were used to identify potential nest predators and assess whether small, farm-scale predator control could reduce mallard nest predation in Southland, New Zealand. Artificial nests were deployed over the mallard nesting period (late winter - spring) in both 2019 and 2020 and monitored with motion detection cameras. Prior to 2020 artificial nest deployment, farm-scale trapping of mammalian predators was conducted on one farm whilst the other was left as a control. Feral cats (Felis catus), brushtail possums (Trichosurus vulpecula), and European hedgehogs (Erinaceus europaeus) frequently visited the artificial nests but seldom preyed on them (i.e. consumed the eggs). Swamp harrier (Circus approximans) were the most common predator and were responsible for the destruction or predation of at least one egg at 17% of the artificial nests. Mammalian predator trapping had no noticeable effect on artificial nest predation, but did reduce the probability an artificial nest was visited by a cat, possum, or hedgehog. Results suggest typical predator control efforts of gamebird hunters does not reduce mallard nest predation, but may reduce nest disturbance and consequently mallard hen predation and nest abandonment.