Can Australian honeyeaters recognise the odours of native and exotic predators?

Many mammalian predators leave volatile chemical signals in the environment. These scent cues can alert prey species to the presence of predators and may elicit fear-like avoidance responses in their native prey. However, naïve prey may not be able to associate a scent with a novel exotic predator, because the length of co-existence between these invasive predators and native prey has been too short. This study investigated the ability of Australian birds to recognise native and exotic predators. We used scented and unscented bird baths as an avian equivalent to a Y-maze, commonly used in scent experiments on rodents and reptiles, to test whether seven species of honeyeaters respond to the odours of a native predator (brush-tailed possum), two exotic predators (cat and brown rat), and a native herbivore (koala). We expected honeyeaters to avoid the odours of native possums, but not the odours of cats and rats, as they have co-existed with these exotic predators for only 100–200 years. Honeyeaters visited baths with possum scent less often than control baths and they also spent less time at these scented baths. Honeyeaters were also less likely to drink or wash in possum-scented baths than in control baths. Honeyeaters also avoided rat- and cat-scented bird baths, but the aversion to these baths was less strong than to possum-scented baths. We demonstrate that some birds, like mammals and reptiles, use olfaction to assess predation risk, but how strongly honeyeaters responded to predator scents varied depending on co-evolutionary history with a predator. Introductions of exotic mammalian predators to islands have caused severe population declines and extinctions of many native species, because naïve island species often do not detect, recognize, or respond to exotic predators appropriately. Many mammals and reptiles use olfaction to assess risk of predation, but few studies have investigated this in birds. Using scented and unscented bird baths, we demonstrated that Australian honeyeaters assess risk of predation through olfaction and adjust their behaviours in response to mammalian predator odours. As their response to the scent of a native predator was stronger than their response to the odours of the exotic predators, we conclude that coexistence with exotic predators for over 100–200 years is necessary for some Australian birds to recognize novel predators by scent.