AUTHORS: Arya J. Sanjar, Southern Illinois University; Brent S. Pease, Southern Illinois University; Michael V. Cove, North Carolina Museum of Natural Sciences
ABSTRACT: Invasive predators have caused extinctions on islands globally and remain a key threat in many ecosystems worldwide. Within the Florida Keys, USA, mammal populations are declining, which can be attributed in part to the presence of invasive Burmese pythons (Python bivattatus) that expanded from Everglades National Park in the 2000s. However, due partially to the species' elusive nature, Burmese python population size is unknown and has not been conclusively linked to mammal population declines as relatively few have successfully monitored the species’ impact, suggesting alternative approaches to the problem are needed. Here, we tested an indirect route to estimating Burmese python impact on mammals in the Florida Keys by radio-collaring Virginia opossums (Didelphis virginiana) - an important food source for pythons in the Keys - and assessing cause-specific mortality in Key Largo, FL. Between May 2023 – Sept 2024. In total, 3,307 nights of trapping effort resulted in 148 collared opossums across the study area. Subsequent VHF monitoring of collared opossums documented 90 mortalities. Overall, 23% (21 individuals) of mortalities were due to vehicle strikes, 17% by Burmese pythons, and 2% by coyotes. 57% of mortalities were either apparent monitoring-related mortalities (5%) or unable to be attributed to a single factor. As a result of our indirect monitoring, to date, 10 individual pythons were removed from the population in Key Largo. These results suggest that monitoring key prey species may be a viable option for indirectly assessing a top, invasive predator’s impact on mammal populations. Additionally, our results indicate that python predation is a notable contributor to opossum mortality, suggesting potential for additive mortality on mammal communities in the region. Future work involves testing this method in various habitats throughout South Florida to assess its viability outside the Florida Keys.
