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In the Field with Eastern Massasauga Rattlesnakes

Much like anyone in the northern hemisphere on the first warm Saturday of the year, each spring the Eastern massasauga rattlesnake (EMR) emerges from the holes that it hibernates in all winter ready for some sun and a good meal to kick-start its growth and reproduction for the year. And each spring, a group of 30 professionals from zoos across North America, universities, and federal and local wildlife agencies gather in Michigan to study the snakes as they’re emerging.

EMR are rare, attractive, rather shy snakes that were once widely distributed in wetlands across the Great Lakes region of the U.S. and Canada. They’ve suffered from habitat loss and fragmentation as wetlands were drained for roads, farms, and development. In addition, persecution from humans – both due to fear of rattlesnakes and through poaching by private collectors, is an ongoing threat. Nearly 40% of historical populations are thought to be locally extinct, and 15% have unknown status. Because of these trends, in 2016 the species was listed as Threatened under the Endangered Species Act, joining its protected status under the Canadian Species at Risk Act.

In our annual fieldwork, we’ve been monitoring the population using mark-recapture methods, and have captured and re-released more than 800 unique individuals over the nine years of our study. That sort of long-term dataset is rare for any species other than long-lived mammals, and especially not for the less “charismatic” species of the world – snakes would top that list in most people’s minds. Such long-term studies on species like EMR are rare because maintaining constant funding over a decade or more can be challenging. EMR don’t congregate together on a breeding ground like penguins or move obviously through the landscape like elephants, and due to their elusive nature an intensive effort must be put in to find individuals.

They, like many snakes, also have a big P.R. issue – when I excitedly tell people that I’m heading to the field to monitor a federally threatened rattlesnake species that we’re helping to conserve, nearly everyone outside the scientific and zoo community wrinkle their nose and ask why I’d want to do that. At Lincoln Park Zoo, we’re For Wildlife. For All. – and we study less loved species like EMR, more loved species like chimpanzees, and hundreds of species in between. Snakes are important predators of mice and other small mammals, and a recently published analysis suggested that every timber rattlesnake removes 2500-4500 ticks through consumption of their hosts – an important contribution to preventing diseases like Lyme disease. Snakes like EMR are also important food sources for raptors and other higher trophic levels. Since EMR were listed as Threatened in 2016, it is necessary to study their long-term population dynamics.

Our field work is essential to continue to understand what’s happening with the population. We gather field surveyors from zoos around the country who participate in the EMR Species Survival Plan (SSP). This group helps manage the population of EMR that live in North American zoos, but also spend over 350 hours surveying for a population in collaboration with the Edward Lowe Foundation in southwest Michigan. Michigan is a stronghold for the species and is centrally located across its range. Despite being a well-studied snake in terms of spatial dynamics (based on radio telemetry), there are very few studies of long-term demographics, and the existing datasets are derived from the extreme southwestern and northeastern corners of EMR range. Since 2009, when we initiated our mark recapture study, more than 800 EMR have been captured, examined, and individually identified before being released back into the habitat. By monitoring these individuals over time, we will better understand demographic rates, population trends, and impact of management actions.

An important emerging area of threat that we’re all studying is snake fungal disease, which may be a conservation challenge for EMR as well as other snake species. For EMR, population declines directly attributed to the disease have been difficult to establish due to the cryptic nature of both the snake and the disease. We recently published a study in the Journal of Wildlife Management (Hileman, et. al.) which evaluates how easy it is to detect the fungus that causes the disease given current non-invasive methods (typically swabbing an individual and then using genetic methods to see if the fungus DNA can be amplified). Unfortunately these methods can also cause “false negatives” – instances where the fungus is present but not detected, or not present but still detected. Using a method of multiple swabs and some sophisticated modeling, we were able to reduce the chance of obtaining those false negative results by 72% when snakes with clinical signs were sampled. This study puts us leaps and bounds – or should I say slithers and slithers – ahead of detecting and managing disease within this threatened population. Luckily at our study population, prevalence rates are low.

In all, the data we’re collecting is going to be invaluable at describing how this population of massasaugas are doing, and should help us understand how to better monitor and preserve populations across the range.

– Lisa Faust, Ph.D., Vice President, Conservation & Science, Lincoln Park Zoo