Invasive Species

Contributed Oral Presentations

Contributed paper sessions will be available on-demand for the duration of the conference, then again at the conclusion of the conference.


Influence of Juniper Cover on Montezuma Quail in Texas
Kristyn G. Stewart; Fidel Hernández; Eric D. Grahmann; Humberto L. Perotto-Baldivieso; Leonard A. Brennan; Robert M. Perez
Montezuma quail (Cyrtonyx montezumae) are a secretive and understudied bird species inhabiting pine-oak (PinusQuercus) communities in the southwestern United States (Texas, Arizona, and New Mexico). In Texas, a small isolated population of Montezuma quail is found in the Edwards Plateau while a larger and more contiguous population is located in the Trans-Pecos Mountains and Basins. Interestingly, Ashe juniper (Juniperus ashei) has increased and created dense stands of woody cover in the Edwards Plateau where the Montezuma quail population is relatively low; however, alligator juniper (Juniperus deppeana) is prevalent throughout the Trans-Pecos Mountains and Basins but with no apparent influence on the species. Our objectives were to compare juniper use by Montezuma quail between these 2 ecoregions. We collected vegetation data at used and random points at the micro- (16 m) and macro-scale (350 m) in both regions and calculated continuous selection functions for juniper. At the micro-scale, Montezuma quail avoided areas with ≥ 20% Ashe juniper cover but selected areas with 8‒50% alligator juniper cover. We documented similar findings at the macro-scale, with Montezuma quail selecting areas with ≤ 30% Ashe juniper cover. The influence of juniper on Montezuma quail appears to vary by species—negative with Ashe juniper but positive with alligator juniper—and may be related to differences in the juniper species’ growth habit and Montezuma quail’s evolutionary history.
The Challenges of Using Camera Trapping for Abundance Estimation of Invasive Herpetofauna
Staci M. Amburgey; Amy A. Yackel Adams; Beth Gardner; Nathan Hostetter; Brett T. McClintock; Shane Siers; Sarah J. Converse
Estimating abundance of invasive species is critical for choosing amongst candidate management actions and assessing success of management efforts, but abundance estimates can be financially and logistically prohibitive to obtain when using traditional approaches such as capture-recapture. Camera traps are heralded as a way to estimate abundance cost-effectively, using spatial capture-recapture (SCR) or related methods when animals possess unique markings and “unmarked” methods when individuals are non-uniquely identifiable. However, lures at camera traps, often essential in obtaining sufficient sample sizes, can violate the assumptions of modeling frameworks. We investigated use of camera traps with lures and “unmarked” methods to estimate the abundance of brown treesnakes (BTS). BTS were accidentally introduced to Guam in the 1940s and have since decimated native fauna. BTS are non-uniquely identifiable in photo-captures, slow-moving, and require the use of lures to adequately sample, challenging the use of camera traps and abundance estimation. To investigate the potential biases associated with lure-use, we developed a suite of scenarios with varying levels of lure-attraction and camera densities. We simulated a correlated random walk movement process for BTS in a confined study area and “sampled” snakes to generate data for analysis with unmarked SCR, REST, and space-to-event models. We found that with the highest lure-attraction and lowest number of cameras, density estimates were highly biased and imprecise under all models. Increasing camera density and decreasing lure-attraction resulted in improved estimates but for all models remained biased. Though all models were sensitive to violations of assumptions, there remains a need for cost-effective methods for invasive species management. Our results indicate that for BTS, we need to include other monitoring methods to optimize monitoring with respect to cost and precision of estimates. With vertebrate reintroductions as an eventual aim in Guam, optimal monitoring strategies will be needed to assess BTS suppression efforts.
A Dynamic Removal Model Incorporating Multiple Capture Methods to Evaluate Invasive Species Management
Amy Davis; Randy Farrar; Brad Jump; Travis Guerrant; Parker Hall; Kim Pepin
Efficient methods for control of feral swine are critical to combat the significant threats that invasive species present to agriculture, natural resources, and livestock and human health. However, it is often difficult to assess the efficacy of control methods due to limited resources. Yet, there are two important reasons to focus effort on evaluation: to provide evidence of the impact resources spent on control activities have had on reducing invasive species and to provide feedback for the continual improvement of management efficiency. To evaluate management actions there is often a trade-off in effort aimed at performing management actions and effort aimed at collecting data to evaluate management actions. We developed a method to estimate invasive species abundance from a combination of removal management activities (e.g., aerial gunning, trapping, ground shooting) using only data collected during removal efforts (the method of removal, the date, location, number of animals removed, and the effort). We analyzed removal data from Mingo National Wildlife Refuge in Missouri from December 2015 to September 2019, where the management objective is elimination. Populations of feral swine on Mingo NWR have fluctuated over time but have shown more marked declines in the last 3-6 months. More dramatic declines were observed in the center of the refuge. To counteract population growth (either through births or immigration) the percent of the population of feral swine removed monthly must be greater than the growth rate. On average, we found that removing 10% of the population monthly had only a 50% chance of causing a population decline, whereas removing 15% of the population monthly had a 95% chance of causing a population decline.
Effects of Imidacloprid Exposure on Aquatic and Terrestrial Salamander Abundances
Sara M. Crayton; Petra B. Wood; Donald J. Brown; Lenza E. Paul; Yong-Lak Park
The neonicotinoid imidacloprid is widely applied in natural systems to manage the spread and impacts of nonnative forest insects, such as hemlock woolly adelgid (Adelges tsugae). While application of this pesticide is an effective management tool for native tree preservation, research has shown it can have negative impacts on non-target invertebrates and vertebrates. However, few studies have assessed vulnerability of amphibians to imidacloprid exposure at environmentally relevant concentrations. In this study, we assessed whether imidacloprid exposure affected aquatic and terrestrial salamander abundances within hemlock communities in West Virginia. We surveyed stream salamanders 5-7 times at 48 study sites located on headwater streams (27 of which had been exposed to imidacloprid treatments) and surveyed terrestrial salamanders 12 – 17 times at 36 terrestrial study sites (18 of which had been exposed to imidacloprid treatments) during 2017-2019. In addition, we collected 107 Desmognathus spp. individuals from 11 of the aquatic sites to assess whether chronic pesticide leaching into adjacent streams resulted in bioaccumulation of imidacloprid in aquatic salamander tissues. We used N-mixture models and a model selection approach to identify important predictors of salamander abundance and detection probability (p) for Desmognathus fuscus, D. monticola, D. ochrophaeus, Eurycea spp., Gyrinophilus porphyriticus, Plethodon cinereus, and P. glutinosus. After accounting for environmental conditions influencing abundance and detection, we assessed and ranked candidate predictors of imidacloprid exposure, including water and soil concentration, occurrence of applications and detected presence in the environment, number of applications, and number of years since imidacloprid treatment. We found that 29 individuals of Desmognathus spp. (26%) had either imidacloprid or an imidacloprid metabolite in their tissues. There was a negative correlation between number of years since treatment and the abundances of D. ochrophaeus adults and G. porphyriticus larva, suggesting that population-level impacts of imidacloprid exposure may be delayed.
Population Decrease in the Small Indian Mongoose in Southwestern Puerto Rico Following a Natural Disaster
Are R. Berentsen; Mel J. Rivera-Rodriguez; Fabiola B. Torres-Toledo; Shylo R. Johnson; Christine K. Ellis; Chad K. Wickham; Richard B. Chipman; Amy T. Gilbert
The small Indian mongoose (Herpestes auropunctatus) is an invasive species and rabies reservoir in Puerto Rico. As part of research into rabies exposure in mongooses, we collected mongoose population density estimates from autumn 2016 – 2019 at two dry-forest sites (Salt Flats and Refuge) at Cabo Rojo National Wildlife Refuge, SW Puerto Rico. We established a 0.5 – 1 km2 plot at each site with a trap density of 100 traps/km2 and checked traps for ten days. We immobilized captured mongooses and implanted a passive integrated transponder tag for individual identification. We estimated population density using the Minimum Number Known Alive (# unique mongooses/km2 of study area) method. In autumn 2016, density estimates were 39 and 38 mongooses/km2 at the Salt Flats and Refuge, respectively. Estimates were slightly higher in spring 2017, with 43 and 53 mongooses/km2 for the Salt Flats and Refuge, respectively. In autumn 2017, hurricane Maria made landfall on Puerto Rico, causing significant island-wide destruction of natural and developed habitats. In spring 2018, mongoose densities had decreased to 13 and 37 mongooses/km2 at the Salt Flats and Refuge, respectively and by autumn 2018 densities decreased further to 6 and 7 mongooses/km2. In autumn 2019, no mongooses were captured at the Salt Flats and remote camera studies photographed no mongooses at the Refuge. A similar reduction in mongoose activity following Hurricanes Irma and Maria was documented in the US Virgin Islands. The mongoose population decline could potentially be attributed to localized flooding (resulting in mortality) followed by reduced food resources and migration. Increases in non-native red-tailed boa constrictors (Boa constrictor), which prey upon mongooses, could also impact mongoose populations. However, suggested boa increases at the Refuge are anecdotal and documentation of the snake’s impact on mongoose populations is unknown.
Movements and Home Range Sizes of Nilgai Antelope: Implications for Management of Cattle Fever Ticks in South Texas
Kathryn M. Sliwa; Jeremy A. Baumgardt; Randy W. DeYoung; J. Alfonso Ortega-S.; David G. Hewitt; John A. Goolsby; Adalberto A. Pérez de León
The resilience of the Cattle Fever Tick Eradication Program (CFTEP) established in 1906 is currently jeopardized by the involvement of nilgai antelope (Boselaphus tragocamelus). This exotic ungulate species was introduced to South Texas in 1924, and has since spread throughout the region where it is estimated 30,000-50,000 individuals exist. Nilgai are alternative hosts of the cattle fever ticks (CFT) Rhipicephalus (Boophilus) microplus and R. (B.) annulatus, which are vectors of the pathogens causing bovine babesiosis in cattle. Although eradicated from the U.S. by 1943, CFT still cause outbreaks in parts of South Texas. Bovine babesiosis is endemic to Mexico, threatening U.S. cattle herds with disease and economic loss to the livestock industry. Nilgai infested with CFT complicates CFTEP operations because their ecology involves long-distance movements. Gaps remain in our knowledge of the movements and home range sizes of nilgai. Therefore, the goals of this study were to 1) determine seasonal home range sizes of nilgai using hourly locations from 26 GPS-collared individuals and 2) examine nilgai movement behaviors. Nilgai had large and highly variable home ranges: males (n=9), median = 693 ha (range=76-4677 ha), females (n=15) median = 529 ha (range=29-5611 ha). Two young females made long-distance movements of over 40 km within a month, sometimes traveling 2-5 km/hr. These movements resemble dispersal behavior which is not common for female ungulates, and may result from the social structure of nilgai, where males are territorial. Large home ranges and long-distance movements by nilgai challenge the sustainability of CFT eradication efforts in the U.S. This is key information the CFTEP can use to adapt new technologies to treat infestations in nilgai.
Interspecific Interactions of Two Invasive Lizards in An Urban Environment
Steve A. Johnson; Camilla A. Rodriguez-Barbosa
Human-modified environments often support a diversity of non-native wildlife. For example, urbanized areas of South Florida are inhabited by numerous species of established, nonnative reptiles. However, trophic interactions among many of these species have not been investigated despite their influence on ecosystem dynamics. We investigated the predator-prey relationship between two invasive species of lizards in an urban setting. Our objectives were to determine if manipulating populations of a predator had any impact on individual and population parameters of the prey species. We performed a field experiment at eight shopping plazas in Broward County, Florida, to investigate how body condition, abundance and survivorship of the introduced Brown Anole (Anolis sagrei) responded to reduction of its predator, the introduced Northern Curly-tailed Lizard (Leiocephalus carinatus). Additionally, we evaluated how reduced predator pressure altered Brown Anole habitat use. We conducted a mark-recapture study to estimate population parameters and included environmental and arthropod diversity as covariates in our analyses. Our results indicate that Brown Anole abundance and survival probability significantly increased after the removal of Northern Curly-tailed Lizards, whereas Brown Anole body condition was influenced only by time. Brown Anoles exhibited a shift in their spatial use by moving to lower stratum levels in absence of the Northern Curly-tailed Lizards. Removing Northern Curly-tailed Lizards presumably released Brown Anoles from predation pressure. Our results provide evidence that Northern Curly-tailed Lizards are intraguild predators of another introduced species in an urban lizard community. They also suggest unintended consequences (i.e. increase in an invasive species—Brown Anole) may occur when removing a species without adequate understanding of the trophic dynamics of the ecosystem in which it is established.
Abundance and Culling Efficacy of Invasive Rose-Ringed Parakeets in Kauai, Hawaii
C. Jane Anderson; William P. Bukoski; Bryan M. Kluever; Page E. Klug; Shane E. Siers; Steven C. Hess; Leonard A. Brennan
The rose-ringed parakeet (Psittacula krameri) is among the most invasive bird species worldwide. Rose-ringed parakeets were introduced to Kauai, Hawaii, in the 1960s. The population initially remained relatively small but began growing in the early 2000s and rapidly increased to an estimated 6,800 individuals in 2018. This population is causing extensive agricultural damage by foraging on fruit and grain crops. The parakeets also congregate nightly in large roosts in urban areas, causing disturbance through loud vocalizations and threatening human property and health through excessive droppings. To address this problem, we are evaluating historic take records and estimating current rose-ringed parakeet abundance in Kauai to estimate the annual population growth rate. Monitoring a roost culling effort from March – June 2020, we are evaluating number of birds taken per unit of effort, age and sex ratio of birds taken, how varying levels of effort could be projected to influence future population size, and whether roost culling instigates roost abandonment. We estimated the 2020 population to include ≥10,500 parakeets, despite the removal of >7,000 individuals in the preceding 15 years. Preliminary results of the roost culling analysis indicate ≥40 animals can be removed per shooter per hour of effort, and that culling at a frequency of ≥ once per week does not appear to elicit roost abandonment. These studies will be incorporated into an integrated pest management plan to reduce the invasive rose-ringed parakeet population and related impacts on Kauai.


Contributed Oral Presentations
Location: Virtual Date: Time: -