Better food-based baits and lures for invasive rats Rattus spp. and the brushtail possum Trichosurus vulpecula: a bioassay on wild, free-ranging animals

Abstract

Food-based baits and lures remain the mainstay of eradication and monitoring methodologies for invasive mammalian species. To date, however, best-practise baits and lures for rats and possums have not been systematically compared to alternative food-based products in ways that quantify their effectiveness on free-ranging, wild animals. We designed a rapid bioassay using chew-cards to present large numbers of food-based products to free-ranging rats and possums to assess their attractiveness and consumption compared to current standards. We used linear mixed-effects regression analysis and an information-theoretic model set to consider the nutritive drivers of consumption for each species with the aim of informing the design of, and future search for, baits. Current standards were statistically outperformed in our trials. For rats, cheese, milk chocolate, Nutella® and walnut were statistically more attractive than the peanut butter standard. For possums, apricot and almond were statistically more attractive that the cinnamon standard. Model comparisons indicate that energy, particularly from fats, is the most important determinant of consumption by rats, while protein is the most important determinant of consumption by possums. Our results demonstrate that current standard lures for both species could be more attractive whilst the inclusion of fat to rat baits and protein to possum baits could increase bait consumption and improve control operation outcomes. Further, our bioassay provides practitioners a cost effective and rapid methodology to systematically assess large numbers of food products on free-ranging, wild animals thus providing more realistic results than those obtained under pen or laboratory conditions.