Natural and synthetic vocalizations of brown rat pups, Rattus norvegicus, enhance attractiveness of bait boxes in laboratory and field experiments

Rattus population genomics across the Haida Gwaii archipelago provides a framework for guiding invasive species management

Invasive species have led to precipitous declines in biodiversity, especially in island systems. Brown (Rattus norvegicus) and black rats (R. rattus) are among the most invasive animals on the planet, with eradication being the primary tool for established island populations. The need for increased research for defining eradication units and monitoring outcomes has been highlighted as a means to maximize success. Haida Gwaii is an archipelago ~100 km off the northern coast of British Columbia, Canada, that hosts globally significant breeding populations of seabirds that are at risk due to invasive rats. Here, we paired sampling of brown (n = 287) and black (n = 291) rats across the Haida Gwaii archipelago with genotyping by sequencing (10,770-27,686 SNPs) to investigate patterns of population connectivity and infer levels/direction of gene flow among invasive rat populations in Haida Gwaii. We reconstructed three regional clusters for both species (north, central and south), with proximate populations within regions being largely more related than those that were more distant, consistent with predictions from island biogeography theory. Population assignment of recently detected individuals post-eradication on Faraday, Murchison and the Bischof Islands revealed all were re-invaders from Lyell Island, rather than being on-island survivors. Based on these results, we identified six eradication units constituting single or clusters of islands that would limit the potential for reinvasion, some of which will need to be combined with biosecurity measures. Overall, our results highlight the importance of targeted research prior to conducting eradications and demonstrate a framework for applying population genomics for guiding invasive species management in island systems.

Testing the potential of 50 kHz rat calls as a species-specific rat attractant

The control of mammalian pests relies heavily on the use of pesticides that are often avoided and are not species-specific. These problems are particularly acute for pesticides used to control rats (Rattus spp.). The efficacy and targeting of control could be improved by attracting animals to control measures using species-specific cues. One cue that has the potential to attract rats is the 50 kHz calls they emit in positive social situations. Here we test the potential of these rat calls as a species-specific attractant by examining the response of laboratory rats (Rattus norvegicus; n = 48) and non-target bank voles (Myodes glareolus; n = 16) to 50 kHz calls from either sex in a compartmentalised laboratory arena. Sounds of rat movement and white noise acted as control treatments, with each sound tested against a silent control in the opposite side of the arena. When sound cues were played above an empty bait box, rats were attracted to spend time close to 50 kHz rat calls, climbing on top of boxes, regardless of the sex of subject or caller. When either 50 kHz rat calls or rat movement sounds were played inside an empty bait box, rats of both sexes spent 3-4 fold more time inside boxes and visited more frequently. Rats were not attracted by intermittent white noise. Bank voles were neither attracted to, nor avoided, 50 kHz rat calls played inside empty bait boxes. Our findings show that 50 kHz rat calls are an effective attractant for rats of both sexes under laboratory conditions, while not attracting non-target bank voles. These calls are strong candidates for providing a species-specific lure that may be attractive even in the absence of food bait, but further trials will be needed to assess their efficacy under field conditions.

Sex Hormones Function as Sex Attractant Pheromones in House Mice and Brown Rats

Sex hormones of mammals control the expression of sexual characteristics and bodily functions. The male hormone testosterone and the female hormones progesterone and estradiol are known to occur in urine markings of mice. Here, we show that all three hormones are also present in urine of brown rats, and that they are effective sexual communication signals (pheromones) that elicit attraction behavior of prospective mates in both brown rats and house mice. When added as lures to trap boxes in field experiments, synthetic testosterone, for example, increased captures of adult female mice 15-fold, and a blend of progesterone and estradiol increased captures of male mice eightfold and male rats 13-fold. Remarkably, these hormones increased captures even though the food- and pheromone-based baits to which they were added had previously been shown to be superior to current commercial rodent attractants. We predict that these sex hormones will function as sex attractant pheromones in diverse taxa.