Rose-ringed Parakeets on Kauai, Hawaii
Rose-ringed parakeets (Psittacula krameri) are one of the most invasive bird species in the world, having established nonnative populations in over 35 countries. While these birds are beautiful, intelligent, and charismatic, they can devastate native species and ecosystems where they are introduced. Further, they cause significant agricultural damage by eating crops. Rose-ringed parakeets were introduced on the island of Kauai, Hawaii, in the 1960s. What began as only a few animals is now in excess of 10,500 birds.
From 2019-2022, I led a study in collaboration with the USDA National Wildlife Research Center to evaluate management options to reduce the rose-ringed parakeet population size on Kauai. This work was funded by the Hawaii State Legislature Senate Bill No. 772, which was passed in response to the impacts the parakeets have caused on the island. Our work included 1) evaluating the efficacy of a roost culling effort – using air rifles to cull parakeets in their large nightly congregations – conducted by a private wildlife control company; 2) efforts to habituate the rose-ringed parakeets to bird feeders to evaluate the potential use of contraceptives; 3) spatial modeling to predict locations on Kauai where the population may spread; 4) evaluating the genetic diversity of rose-ringed parakeets on Kauai, relatedness to a population on Oahu, and how this information could be used to guide future rose-ringed parakeet population management in Hawaii. My collaborators and I consolidated this information into a recommended management plan for rose-ringed parakeets on Kauai. This plan is currently in review by the state of Hawaii and will be shared here when it is publicly-available.
Ocelots in South Texas
Ocelots (Leopardus pardalis) are a medium-sized felid native throughout Central and South America. Once widespread throughout Texas, Louisiana, and Arkansas, the U.S. population of the federally endangered ocelot is now restricted to the Lower Rio Grande Valley (LRGV) of South Texas. It is estimated <80 individuals remain between two genetically isolated breeding populations. While the population decline is due to several factors, vehicle collisions have been found to be one of the leading contemporary causes of ocelot mortality in the LRGV. Wildlife crossing structures may provide a viable mitigation strategy but must be placed in locations that maximize likelihood of use by ocelots.
From 2018 – 2019, I led a team contracted by the Texas Department of Transportation to provide guidance on optimal locations to build wildlife crossing structures to protect ocelots in the LRGV. My team and I analyzed an ocelot telemetry dataset spanning 35 years coupled with transportation data to conduct several studies to address this goal. We evaluated landscape features at locations where ocelots frequently cross roads and where they have been struck by cars and found ocelots are likely to cross roads which bisect large woody patches (their preferred habitat). We also evaluated behavioral patterns in ocelot road-crossing patterns (no surprise, risk-prone males cross more often than females!). This information is now being used by TxDOT to inform future roadway mitigation strategies to protect ocelots.
Invasive Monkeys in Florida
Humans have introduced other primate species to new places for at least five centuries. In the U.S., people have introduced 10 species of primates ranging from lemurs to chimpanzees. Three species of primates have been introduced into Florida: rhesus macaques (Macaca mulatta), vervet monkeys (Chlorocebus sabaeus), and squirrel monkeys (Saimiri sciureus). As a Ph.D. student, I led a team that described the history and status of these species. We noticed an interesting trend; despite having the most introduced populations, squirrel monkeys had had the least success in establishment in the state. Conversely, the vervet monkey population had remained remarkably stable, and introduced rhesus macaque populations in both the forests of central Florida and the mangrove islands of the Florida Keys had thrived.
Climate envelope models are a unique tool to understand the climatic variables that defines a species’ range. We developed climate envelope models to characterize the climatic conditions in which the three monkey species occur in their native range, and then compared these to the conditions in Florida. Our models indicated the climatic conditions within Florida and throughout much of the southeastern U.S. are similar to those of each species’ native range. Interestingly, this suggests climate is not the limiting factor of squirrel monkey survival or vervet monkey spread in Florida. It also suggests climate will not limit continued spread of rhesus macaques. This information can be used to prioritize use of limited research and management funds.
Invasive Rhesus Macaques in Florida
Rhesus macaques are a medium-size monkey. Spanning west to Afghanistan and east to the Pacific coast of China, they have the largest native range – or area in which a species naturally occurs – of any primate other than humans; this means they have adapted the ability to thrive in a diversity of habitats, including the frigid foothills of the Himalayas and arid semi-deserts of India. This ability to survive just about anywhere means they are also adept at invading new habitats when they are introduced. Approximately 10 rhesus macaques were introduced in what is today Silver Springs State Park, central Florida, in the 1930s and 1940s in an effort to increase tourism. This population has demonstrated considerable growth and reached ~400 individuals by the mid-1980s. From that time until 2012, the population was controlled through a trapping and removal program, but no population control has been implemented for the past decade. From 2012 – 2018, I led several studies of this population.
From 2011 – 2016, there were ≥38 observations of rhesus macaques in Florida outside of Silver Springs State Park. It is unknown whether these individuals represented separate introductions or if they were emigrants from the Silver Springs population. To evaluate the genetic diversity of rhesus macaques in Florida, we presented cotton swabs soaked in sucrose (i.e., snow cone syrup) to the macaques; the macaques chewed the swabs until they lost flavor, then spit out the swabs. We then collected the swabs and extracted DNA from the residual macaque saliva. We used genetic sequencing to characterize the mitochondrial genetic composition of this population. We described five haplotypes within the population, supporting the notion all members of the current population came from small, isolated introductions. Further, we collected a sample from an adult male rhesus macaque captured >100km from the Silver Springs population and determined he had a haplotype identical to members of the population. This indicates males may be dispersing great distances from the source population.
Capybaras in Florida
Native throughout South America, the capybara (Hydrochoerus hydrochaeris) is the world’s largest rodent. This species has recently expanded its native range in Paraguay. Further, it has been regularly observed since 1992 throughout Florida, U.S.A, where at least one introduced population included ~60 individuals. Given the potential impacts capybaras could have on native species and demonstrated ability to establish in Florida, we sought to evaluate whether climate throughout Florida and the southeastern U.S. is conducive to capybara requirements. We developed a climate envelope model (methodology described above) and determined climatic conditions expanding Florida and much southeastern U.S. are unlikely to curtain capybara establishment. Our results suggest managers should make efforts to quickly control future capybara introductions.
When an animal enters an environment, it leaves bits of its DNA through hair, skin, or bodily fluids; this is referred to as environmental DNA (eDNA). Detecting eDNA in water or soil is a novel technique for detecting cryptic species. Essentially, it allows us to determine whether an animal has entered a habitat without actually observing the animal. Researchers are now refining this tool to understand how long eDNA persists in different environments and how to best use to detect different species. Given the potential for capybaras to establish populations in Florida, managers need a low-cost and efficient mechanism to detect potential future introductions. In this study, we sought to develop an eDNA assay for the detection of capybaras in novel environments. In summer 2017, we conducted a pilot study using water from a capybara exhibit from the Rolling Hills Zoo, preserved with Longmire’s solution; we were able to successfully extract capybara DNA from the water sample, even after leaving it untouched for 85 days after initial collection. To determine if this method would work under varying environmental conditions and water body sizes, we collected samples of capybara scat from the Jacksonville Zoo and placed it in water bodies in the lab and in the field. We found we were able to detect eDNA in all water bodies, but the duration of detection varied. Future research can expand these results in environments where capybara have been introduced to better understand how the assay works in natural habitats.