Evaluating GPS biologging technology for studying spatial ecology of large constricting snakes

Abstract

Background: GPS telemetry has revolutionized the study of animal spatial ecology in the last two decades. Until recently, it has mainly been deployed on large mammals and birds, but the technology is rapidly becoming miniaturized, and applications in diverse taxa are becoming possible. Large constricting snakes are top predators in their ecosystems, and accordingly they are often a management priority, whether their populations are threatened or invasive. Fine-scale GPS tracking datasets could greatly improve our ability to understand and manage these snakes, but the ability of this new technology to deliver high-quality data in this system is unproven. In order to evaluate GPS technology in large constrictors, we GPS-tagged 13 Burmese pythons (Python bivittatus) in Everglades National Park and deployed an additional 7 GPS tags on stationary platforms to evaluate habitat-driven biases in GPS locations. Both python and test platform GPS tags were programmed to attempt a GPS fix every 90 min.Results: While overall fix rates for the tagged pythons were low (18.1%), we were still able to obtain an average of 14.5 locations/animal/week, a large improvement over once-weekly VHF tracking. We found overall accuracy and precision to be very good (mean accuracy = 7.3 m, mean precision = 12.9 m), but a very few imprecise locations were still recorded (0.2% of locations with precision > 1.0 km). We found that dense vegetation did decrease fix rate, but we concluded that the low observed fix rate was also due to python microhabitat selection underground or underwater. Half of our recovered pythons were either missing their tag or the tag had malfunctioned, resulting in no data being recovered.Conclusions: GPS biologging technology is a promising tool for obtaining frequent, accurate, and precise locations of large constricting snakes. We recommend future studies couple GPS telemetry with frequent VHF locations in order to reduce bias and limit the impact of catastrophic failures on data collection, and we recommend improvements to GPS tag design to lessen the frequency of these failures.

Reptiles on the wrong track? Moving beyond traditional estimators with dynamic Brownian Bridge Movement Models

“…Each regime progressively lowered the available data ( n reg 2 = 1460 data points, n reg 3 = 730, n reg 4 = 365, n reg 5 = 104, n reg 6 = 52, n reg 7 = 12), while regime 8 varied for each species and individual due to the variability in sheltering and resting behaviour ( n species 1 = 5189 ± 204 data points (mean ± SD); n species 2 = 3501 ± 1099; n species 3 = 3873 ± 573). Visual validation of movement patterns matched with reported patterns in the literature (e.g., [ 11 , 28 , 31 , 70 – 74 ]), and the predicted patterns of the three archetypes (Fig. 2 ).…”

“…The method creates a one-dimensional fix-frequency independent behavioural measure (Brownian motion variance [ 20 ]) that has been employed to elucidate avian and mammal movement patterns and provides a confidence region of where the movement pathways fall (e.g., [ 21 – 24 ]). While tracking reptiles with GPS may currently be limited (see [ 25 – 28 ]) by their natural history [ 29 , 30 ] —e.g. weakened signal due to the surgical implantation, attachment of the tag, limited number of species which can be ethically attached due to body size [ 28 ], reduced fix rates and precision due to underground sheltering [ 16 , 30 ]— leveraging dBBMMs may still benefit reptile VHF studies [ 31 , 32 ].…”

“…While tracking reptiles with GPS may currently be limited (see [ 25 – 28 ]) by their natural history [ 29 , 30 ] —e.g. weakened signal due to the surgical implantation, attachment of the tag, limited number of species which can be ethically attached due to body size [ 28 ], reduced fix rates and precision due to underground sheltering [ 16 , 30 ]— leveraging dBBMMs may still benefit reptile VHF studies [ 31 , 32 ]. Multiple simulations studies have investigated how different methods interact with animal movement and space-use delineation (e.g., [ 18 , 33 – 35 ]), but none have targeted reptile-specific movement patterns.…”

Using dynamic Brownian Bridge Movement Models to identify home range size and movement patterns in king cobras

“…Spatial ecologists have developed numerous methods to study movement patterns which can inform conservation management, particularly with the introduction of GPS telemetry technology [ 9 , 10 ]. The use of GPS tagging is still uncommon for reptiles, particularly in the case of snakes (see [ 11 , 12 ]). Compared to VHF transmitters, current GPS tags have several drawbacks such a larger tag sizes, reduced battery life, and cost per unit.…”

“…For snake species that require highly forested areas with dense vegetation and that shelters underground in burrows or man-made structures [ 13 , 14 ], the fix success rate of GPS tags would still be recurrently low. This problem is particularly relevant for species, such as snakes, that require surgical implantation of the transmitter, which also leads to a significantly weakened GPS signal [ 12 ] (Smith et al 2018). Reptile studies in particular have no consensus pertaining to preferred methods for assessing spatial ecology [ 15 ].…”