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Interspecific interactions are crucial in shaping ecosystem dynamics (Connell 1983, Tilman 1987, Barbosa and Castellanos 2005). Non-native ungulates have been introduced across the globe (Ferretti and Lovari 2014, Volery et al. 2021) and in environments where multiple invasives thrive, these co-occurring sympatric species may shift spatiotemporal patterns to minimize interspecific competition (Schoener 1974, Chesson 2000). Spatiotemporal shifts can lead to cascading effects to the native flora and fauna (Simberloff and Von Holle 1999). Given the potential negative impacts, understanding these interactions is vital for effective management of these ecosystems. Two invasive ungulates, the wild pig (Sus scrofa) and the Philippine deer (Rusa marianna), have inhabited much of Guam since their introduction in the 1600s and 1700s (Intoh 1986, Wiles et al. 1999) and both have been associated with significant ecological damage throughout the island (Conroy 1989). Despite sharing similar invasive roles, they seemingly coexist throughout areas of Guam. Subsequently, efforts are increasingly put forth to remove both species from partitioned areas at one time. To aid these efforts and understand invasive species interactions, we studied the seasonal spatiotemporal patterns of wild pigs and Philippine deer during February 2021-March 2022. Specifically, we used GPS collars from 39 wild pigs and 22 deer to examine spatial and temporal partitioning and assess dynamic spatiotemporal interactions between interspecific dyads at seasonal scales. We investigated spatial partitioning of wild pigs and deer by estimating the spatial overlap between home ranges and core areas of interspecific neighboring dyads. We estimated temporal overlap in diel activity to evaluate temporal partitioning between the species. Lastly, we examined dynamic spatiotemporal interactions, those that occur simultaneously in space and time, by estimating movement interactions between neighboring interspecific dyads to understand attraction and avoidance. We found spatial overlap between the species decreased significantly in core areas compared to home ranges in both seasons. Within home ranges, deer were approximately 3 times more likely to be within pig ranges than vice versa. This effect diminished at core areas such that deer were only 1.3× more likely to be within pig core ranges than vice versa. Temporal overlap of activity between wild pigs and deer was very high during dry and wet seasons, with overlapping activity peaks during crepuscular hours. At a critical distance threshold of 50m, we estimated 77 movement interactions from 58 dyad pairs over 3 seasons and found that only 2 (2.6%) and 4 (5.2%) movement interactions were considered avoidant and attractive, respectively, and the remaining 71 interactions (92.2%) were neutral.

Biomarkers have been used to quantify consumption of toxicants and other pharmaceutical baits by free ranging wildlife populations. Previous research has tested the efficacy and persistence of Rhodamine B (RB) as a biomarker in invasive wild pigs. However, little information is available about effects of RB on palatability of baits meant for invasive wild pigs, and studies have shown that the addition of RB to otherwise palatable baits reduces consumption by some species. HOGGONE® has been identified as an effective sodium nitrite-based oral toxicant for invasive wild pigs in trials conducted in captive pen trials. We simultaneously conducted five separate 2-choice tests to examine potential differences in consumption between HOGGONE® placebo paste (standard placebo) and HOGGONE® placebo paste containing 0.5% RB (RB placebo) in five groups of three invasive wild pigs. Each group was simultaneously presented with equal amounts of standard placebo and RB placebo paste for one night and monitored with remote cameras. Remaining bait was weighed and subtracted from the initial weight of both feed types to calculate consumption. There were no differences in the total amount of bait consumed or the time spent feeding between the two bait types across all five groups. Results of this study suggest that the addition of RB does not negatively impact consumption of HOGGONE® placebo paste by groups of invasive wild pigs. Thus, we provide more evidence that RB will be a useful tool for research on wild pigs, such as estimating proportions of free-ranging populations consuming baits that contain toxins or pharmaceuticals.

Invasive wild pigs (Sus scrofa) are a widely distributed and destructive invasive species throughout parts of North America, Australia, South America, Africa, and many island nations (Barrios-Garcia and Ballari 2012). The invasion of wild pigs is associated with extensive agricultural, ecological, and control costs (Hone 1995, Pimentel et al. 2000, Pimentel 2007). Wild pigs are expanding in distribution and population density throughout the United States and Australia (Bevins et al. 2014, Lewis et al. 2017, Snow et al. 2017b). These increases are attributed to intentional and accidental introductions by humans (Spencer and Hampton 2005, Barrios-Garcia and Ballari 2012), high reproductive potential (Mayer and Brisbin 2009), lack of predators (Bevins et al. 2014), human alterations to the landscape that improve suitability for wild pigs, and the adaptability of wild pigs to occupy a variety of landscapes and opportunistically feed on many food items (Seward et al. 2004). An international effort to develop an acute and humane toxic bait for invasive wild pigs is underway to assist in curtailing their expansion (Snow et al. 2017a). We evaluated the ability to expose a population of wild pigs to a simulated toxic bait (i.e., placebo bait containing a biomarker, rhodamine B, in lieu of the toxic ingredient) to gain insight on potential population reduction. We used 28 GPS collars and sampled 428 wild pigs to examine their vibrissae for evidence of consuming the bait. Overall, we found that (74.1%) of wild pigs tested were positive for RB from consuming the RB bait. These wild pigs were sampled from an average distance of 0.61 km (SE = 0.04) from the nearest bait sites. We estimated that 91% of wild pigs within 0.75 km of bait sites (total area = 16.8 km2) consumed the simulated toxic bait, exposing them to possible lethal effects. Bait sites spaced 0.75-1.5 km apart achieved optimal delivery of the bait, but wild pigs ranging ≥3 km away were susceptible. Use of wild pig-specific bait stations resulted in no non-target species directly accessing the bait. Most of the collared wild pigs visited >1 bait sites during the final night with biomarker deployment, leading to two relevant conclusions. First, the 18-day baiting strategy for locating, and accustoming wild pigs to the placebo bait and bait stations, was adequate for overcoming neophobic tendencies of wild pigs. Secondly, the spacing of the bait stations (i.e., 1 bait site per 0.75 km2) was adequate for exposing all wild pigs in between bait sites to the bait, and may have been expanded to expose more wild pigs. This study demonstrated the potential for exposing a large proportion of wild pigs to a toxic bait. Bait sites should be spaced 0.75-1.5 km apart, and closer will provide better efficacy. Approximately 18 days of coordinated pre-baiting should be sufficient for accustoming wild pigs to using the wild pig-specific bait stations and readily consuming a novel bait. Toxic baits may be an effective tool for reducing wild pigs especially if used as part of an integrated pest management strategy. Investigation of risks associated with a field-deployment of the toxic bait is needed.

Registration of a new toxicant for feral swine in the United States requires meeting test standards under the Federal Insecticide, Fungicide, and Rodenticide Act as regulated by the U.S. Environmental Protection Agency. A primary requirement is to compare the palatability and efficacy of the toxicant to a non-toxic challenge diet in a 2-choice test; however, no standardized challenge diet exists for feral swine. We conducted a series of 2-choice tests to examine four potential challenge diet items for preference by feral swine. We found that feral swine consumed the most and spent the most time feeding on rough rice (i.e., seed rice), although dog food and rough rye could not be wholly discounted as potential challenge diets. Rough rice was preferred, provided adequate nourishment, and is readily consumed by free-ranging feral swine. Therefore, we conclude that rough rice is an appropriate challenge diet for incorporating into 2-choice tests to meet test standards for evaluating the effectiveness of an oral toxicant for feral swine.

While it is known that voles will damage seedlings, we do not know the extent to which deer mice and house mice damage seedlings. Knowing this information can assist resource managers in better targeting problem species and implementing appropriate management actions. We planted and monitored ponderosa pine and narrow-leaf cottonwood seedlings in metal stock tanks occupied by deer mice or house mice to assess the potential for damage by these rodents. Both species damaged leaves and stems of cottonwood seedlings, but house mice did more damage. House mouse damage resulted in mortality of over half of the cottonwood seedlings, while deer mice caused a much lower level of seedling mortality. Only slight damage was done by either species to pine seedlings. Neither species damaged the roots of seedlings, despite the extensive burrowing by house mice. While voles are often considered to be the primary rodent species causing seedling damage, we have shown that deer mice, and especially house mice, could also cause substantial damage to deciduous seedlings. However, our work suggests that rodent control to prevent damage to conifer seedlings might not be warranted in general unless extenuating circumstances and the species causing the damage are identified to assist with targeting control methods more precisely.

Native to the eastern United States, American bullfrogs have been introduced throughout the western U.S. and to several other countries and islands around the world. Bullfrogs are well adapted for many of the permanent water sources that occur within the U.S., and once introduced, they typically become dominant. Because of their large size and voracious appetite, bullfrogs outcompete and prey upon many indigenous species. They are hypothesized to be cause significant negative impacts, which may contribute to the endangerment and extinction of some sensitive species. There are few, if any, effective and efficient control methods to manage invasive bullfrogs. Current methods such as hand or net capture, shooting, and gigging can be labor intensive and often fail to reduce bullfrog numbers. Draining wetland habitats and broadcasting toxicants have severe negative effects on non-target species. New management options, such as locally-sprayed toxicants and multiple-capture traps, could be useful for reducing populations of invasive bullfrogs. However, researchers should make certain that non-target species are not affected by these management techniques.

Following the escape of 8 Gambian giant pouched rats (Gambian rats) from an exotic pet breeder in 1999, Gambian rats became an established invasive species that persists in the wild on Grassy Key, Florida. Because of their large body size, the free-ranging Gambian rats pose a serious threat to native species and agricultural crops, especially if they find their way into mainland Florida. Initiated in 2005, the USDA Wildlife Services has been conducting an eradication and detection program in the Florida Keys. Today however, detecting, baiting, trapping, and removing the now sparse population of Gambian rats are proving difficult. Therefore, we conducted a laboratory trial with wild-captured Gambian rats from Grassy Kay to test 15 potential materials that could be used for attracting the remaining free-ranging population. We found that a conspecific scent (i.e., feces and urine) from other Gambian rats was the most attractive, but also peanut butter, anise, ginger, and fatty acid scent seemed to attract Gambian rats. In an additional study, we tested the efficacy of 6 commercially available rodenticide baits (all with different formulations of active ingredients) in multiple-choice food trials. We found that brodifacoum (second-generation anticoagulant) and zinc phosphide (acute rodenticide) formulated baits were highly effective. Using these various attractants and rodenticides could be useful for eliminating the sparse population of invading Gambian rats in the Florida Keys.

Background: In 2018, a sodium nitrite (SN)‐based toxic bait for invasive wild pigs (hereafter wild pigs; Sus scrofa), was evaluated to determine its effectiveness in reducing local wild pig populations in Texas. Localized population reductions of >70% were achieved, but spillage of bait outside wild pig‐specific feeders (bait stations) caused by feeding wild pigs resulted in the deaths of non‐target animals. To evaluate risks to non‐target animals, we tested whether bait presentation influenced the total amount of bait spilled by wild pigs and estimated the associated risk to non‐target species. Results: We found that bait spilled outside bait stations could be reduced by >90% when compacted in trays, as opposed to being manually crumbled into pieces. We documented a mean spill rate of 0.913 g of bait per wild pig. Conservative risk assessments for nine non‐target species for which SN toxicity data exist indicate that there is relatively low risk of lethal exposure, apart from zebra finches (Taeniopygia guttata) and white mice. Our results indicate that there may be enough spilled bait per feeding wild pig to kill 9.5 or 3.5 individuals of these species, respectively. Other species assessed range from 0.002 to 0.406 potential mortalities per wild pig. Conclusion: We demonstrated that the amount of bait spilled by wild pigs during feeding and the associated risk to non‐target animals can be minimized by presenting the bait compacted in trays within bait stations. We recommend that baits be tightly compacted and secured in bait stations to minimize risks to non‐target animals from spilled bait by wild pigs. © 2023 Society of Chemical Industry. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Although it is known that voles will damage seedlings, we do not know the extent to which deer mice (Peromy-scus spp.) and house mice (Mus musculus Linnaeus, 1758) damage seedlings. Knowing this information can assist resource managers in better targeting problem species and implementing appropriate management actions. We planted and monitored ponderosa pine (Pinus ponderosa Douglas ex Lawson & C. Lawson) and narrow-leaf cottonwood (Populus angustifolia E. James) seedlings in metal stock tanks occupied by deer mice or house mice to assess the potential for damage by these rodents. Both species damaged leaves and stems of cottonwood seedlings, but house mice did more damage. House mouse damage resulted in mortality of over half of the cottonwood seedlings, whereas deer mice caused a much lower level of seedling mortality. Only slight damage was done by either species to pine seedlings. Neither species damaged the roots of seedlings, despite the extensive burrowing by house mice. Although voles are often considered to be the primary rodent species causing seedling damage, we have shown that deer mice and especially house mice could also cause substantial damage to deciduous seedlings. However, our work suggests that rodent control to prevent damage to conifer seedlings might not be warranted in general unless there are extenuating circumstances and the species causing the damage are identified to assist with targeting control methods more precisely. Resume: Bien qu'on sache que les campagnols peuvent endommager les semis, on ne sait pas dans quelle mesure la souris sylvestre (Peromyscus spp.) et la souris domestique (Mus musculus Linnaeus, 1758) causent egalement des dommages aux semis. La reponse a cette question pourrait aider les gestionnaires a mieux cibler les especes problematiques et a mettre en auvre des actions d'amenagement appropriees. Nous avons mis en terre et suivi des semis de pin ponderosa (Pinus ponderosa Douglas ex Lawson & C. Lawson) et de peuplier a feuilles etroites (Populus angustifolia E. James) dans des bacs de rangement en metal occupes par des souris sylvestres ou des souris domestiques pour evaluer les dommages que peuvent causer ces rongeurs. Les deux especes ont cause des dommages aux feuilles et a la tige des peupliers a feuilles etroites. Les dommages causes par la souris domestique etaient nettement plus marques, provoquant la mort de plus de la moitie des semis de peuplier a feuilles etroites tandis que la souris sylvestre causait beaucoup moins de mortalite. Les deux especes de souris ont seulement cause des dommages mineurs aux semis de pin. Aucun dommage aux racines n'a ete observe, meme si la souris domestique creusait beaucoup de terriers. Bien que les campagnols soient souvent pereus comme l'espece de rongeur qui cause le plus de dommages aux semis, notre etude montre que la souris sylvestre et surtout la souris domestique peuvent aussi causer des dommages considerables aux semis des essences feuillus. Toutefois, nos resultats indiquent que la repression des rongeurs pour prevenir les dommages aux semis des coniferes n'est en general pas justifiee, sauf dans des cas speciaux et lorsque les especes qui causent les dommages sont identifiees de maniere a mieux cibler les methodes de repression. [Traduit par la Redaction], Introduction Rodents cause significant damage to a variety of resources required by a growing human population (Witmer and Singleton 2010). Damage can be especially severe when rodent population densities are [...]