What evidence exists on the effectiveness of different types of olfactory lures as attractants for invasive mammalian predators? A systematic map protocol.
Background: Alien mammalian predators are a major cause of species extinction and decline globally. Baits and lures, usually human-food based (for example meat, nuts or oils), are widely deployed in trapping programs to attract target species, but their effectiveness compared to other types of olfactory lures, for example social odours or prey odours, has never been systematically examined. Depending on the context, there can be high proportions of non-target captures, for example when targeting feral cats using cage traps, or low capture success, for example, when targeting introduced rats on tropical islands. Here we use a systematic process to map evidence on the effectiveness of different categories of olfactory attractants for invasive mammalian predators within different ecological contexts. We aim to look for where evidence clusters and knowledge gaps occur, for example, across different lure types or across different habitat-types, and highlight opportunities for future research into behaviourally-relevant olfactory lures. Methods: We will compile evidence from bibliographic databases, online search engines, government websites, specialist sites and expert contacts, and include 'grey' literature. Where possible, a Boolean-style full search string will be used, including Population, Intervention and Outcome search terms. Searches will be conducted in English, but a public request to the IUCN SSC Invasive Species Specialist Group (ISSG) will be made for literature including in languages other than English. Search comprehensiveness will be evaluated against 25 benchmark articles known to the authors. We will base inclusion of articles on presence of quantitative data, subject identity (invasive mammalian predator species), comparator (more than one type of olfactory lure assessed or lure compared to a control) and outcome (quantified attraction to lures or controls). Inclusion consistency checks will be performed with 10% of the titles and abstracts and 10% of the full texts. We will critically appraise the literature only on the basis of study design (e.g. appropriate controls) and sample size, rather than interpret the results. Finally, we will develop a searchable literature database accompanied by systematic 'heat' maps to visually represent knowledge clusters and gaps within different subsets of evidence, and a narrative synthesis of the evidence.