Friday, March 11, 2016

GPS My Rattlesnake: A New and Exciting Research Project!

This is a re-post from a site created by Alex Bently (, an aspiring herpetologist who has started an ambitious project that uses GPS technology to track rattlesnakes. He is hoping to secure more funding for his work. Please consider donating. All the information below was written by Alex and can be found on his project website.  

Project Background

The field of Herpetology was revolutionized in the early 1970’s through the use of radio-telemetry (Újvári and Korsós, 2000), which, for the first time, allowed biologists to gather long-term detailed data on animal life histories, including home range size, activity patterns, intraspecific interactions, hibernacula use, and thermoregulatory behavior (Nathan et al., 2008; Ward et al. 2013). Recent advancements in GPS technology, however, have provided biologists with an exciting new window into the lives of animals (Cagnacci et al., 2010; Recio et al., 2011; Tomkiewicz et al., 2010; Urbano et al., 2010; Ward et al., 2013). Due to size issues, GPS tracking has typically been limited to use with large mammals (Recio et al., 2011), but new improvements in miniaturized technology has opened even more doors for novel applications.

Biologist with a radiotelemetry receiver. 

Admittedly, the unique body shape of snakes (e.g. long, cylindrical body and absence of limbs) poses unique challenges in attaching any external unit. Even so, biologists are beginning to experiment with this methodology and are finding some success (Ciofi and Chelazzi, 1991; Madrid-Sotelo and García-Aguayo, 2008; Wolfe unpub., 2016; Wylie et al., 2011). For example, Ernst (2003) used tape and 5-minute epoxy to attach transmitters to the rattles of Prairie Rattlesnakes. Other forms of attachment have been applied to the upper surface of snakes. However, no publications to date report the use of GPS tracking in any snake taxa even though this methodology has great potential to again revolutionize snake field studies, it just needs to be tested.

A beautiful Timber Rattlesnake (Crotalus horridus)

The Timber Rattlesnake, Crotalus horridus, has been a model organism in numerous studies (Clark, 2002). In fact, C. horridus was one of the first snakes species to be studied using radio-telemetry (Brown et al., 1982; Galligan and Dunson, 1979). This large-bodied pitviper snake is native to much of the eastern United States, and can be locally abundant sometimes occurring in great numbers at communal den and gestation sites. Throughout much of its range, individuals emerge from hibernation between the months of March and May, and remain active for five to seven months, with males spending their active season foraging for prey (mainly small mammals) and searching for mates. Females reproduce every three or four years (Martin, 1993) and during reproductive years they gather at gestation sites known as rookeries. These rookery sites, as well as hibernacula, are selected by snakes based on various geographical features such as aspect, slope, proximity to human disturbance, rock formations and more.

Researchers have found a high level of specialization in these snakes. For instance, individuals use chemical cues to track rodent movements and foraging locations (Clark, 2004; 2007). Furthermore, snake foraging positions and locations are specifically selected based on these chemical cues. So while most people think of snakes such as the Timber Rattlesnake as small-brained, “hard-wired” creatures, as we discover more about the complex functions and secretive lives it’s becoming clear that these snakes are highly sophisticated and specialized on many levels.

Moreover, C. horridus is a key stone species where it is found, playing a critical role in the ecological function of various habitats. Complex relationships have been noted between the presence of gypsy moths, cycles in oak mast production, variation in rodent populations, and Timber Rattlesnakes (McGowan and Martin, 2004). Crotalus horridus is an apex predator responsible for maintaining ecological equilibrium. A number of factors, including their ecological importance, physiological specialization, and relative wide spread abundance make the Timber Rattlesnake an appropriate organism for a wide range of ecological and biological studies. Furthermore, Crotalus horridus, should be an organism apt for testing the viability of GPS tracking in snakes.

What More Info Can GPS Tracking Offer?

Radio tracking still produces valuable data, however advances in technology have provided other tools for wildlife tracking that have the potential to resolve some limitations of telemtry. Among these, the use of GPS has emerged as a viable option for wildlife tracking. (Cognacci et al. 2010; Tomkiewicz et al. 2010; Ward et al. 2013). GPS tracking has several advantages over radiotelemetry. One such advantage is continuous data transmission through a number of mediums (cellular, bluetooth, and wi-fi). Moreover, the ability to obtain position time series data representing movement paths affords biologists more data and greater insights into the spatial ecology of organisms (Nathan et al. 2008). Position time data can now be obtained from a distance without disturbing the animals being tracked. Some GPS units, such as those that I will be using, have a “smart GPS” function, which logs position time data only when the animal moves a specified distance! The possibilities for field based applications are endless with this type of technology.

Custom designed GPS transmitters will be attached to snakes'
rattles using epoxy, tape, and light-weight zip ties. We hope
they stand up to field conditions!
Automated receiving units (ARU) have been used as an alternative to radiotelemetry in several snake studies, but have, in some cases, reported estimated accuracy of positions to 42 meters (Ward et al. 2013). Furthermore ARU is extremely expensive and can produces unreliable data as a result of “postural” changes in snakes and more.

Currently, GPS has been miniaturized to the point of telemetry, and thus is an option for  tracking much smaller animals. This method has  been applied to various mammals and birds (Tomkiewicz et al., 2010), however very little GPS tracking has been done with reptiles. Ashleigh Wolfe, a Ph.D. student at Curtin University, recently tested GPS tracking on Dugite snakes and experienced relative success in obtaining data (Wolfe personal correspondence, 2016). Wolfe implemented an attachment technique following that described by Ciofi and colleagues (1991), who also successfully gathered data from snakes with externally attached tracking units (radiotelemeters in this case). Ernst (2003, 2004) attached radio transmitters to the rattles of Prairie Rattlesnakes, Crotalus viridis. Rattle attachment is not a novel technique, but it’s never been done with GPS transmitters! GPS has the potential to once again revolutionize the field of wildlife biology. Now that the technology exists, the next step in snake tracking is to incorporate GPS.

A Timber Rattlesnake coiled in a mixed-hardword forest.
Such forests are often dominated by oak tree species. 

Alex's project has three goals: 

  1. Test the application of GPS snake tracking by successfully tracking a population of Timber Rattlesnakes
  2. Determine if small scale population migrations made by rodents influence foraging patterns in Timber Rattlesnakes 
  3. Investigate whether oak-mast fluctuations influence rattlesnake populations through their effects on rodent populations (rattlesnake's prey).
To learn even more about the project, watch the YouTube video below or visit to project website. With your help, we can learn even more about these mysterious and ecologically important creatures!

To support the project visit:

Please feel free to contact Alex with questions or concerns!