The field of Herpetology was revolutionized in the early 1970’s through the use of radiotelemetry (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 thechnology has opened even more doors for novel applications.
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; Martin unpub., 2010; 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.
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, individualsemerge 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.
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–Wylie GD, Smith JJ, Amarello M, and Cassazza ML (2011). A taping method for external transmitter attachment on aquatic snakes. Herpetological Review. 42(2):187-191