Home range, habitat use, and movement patterns of non-native Burmese pythons in Everglades National Park, Florida, USA

Abstract

Background: Studies on the spatial ecology of invasive species provide critical information for conservation managers such as habitat preferences and identification of native species at risk of predation. To understand the spatial ecology of non-native Burmese pythons (Python molurus bivittatus), now well-established in Everglades National Park and much of South Florida USA, we radio-tracked 19 wild-caught adult pythons, 16 with VHF tags during 2006 through 2009 and 3 by GPS tags between 2010 and 2011. Our goal was to identify individual core-use areas and quantify home ranges, as well as to explore correlations of python movements with environmental parameters such as the presence of surface water. Results: Radio-tracking periods ranged from 87 to 697 days for snakes with VHF tags, with a total of 5,119 tracking days (mean ± 1 SD = 319.9 ± 184.3 days); GPS tracking periods ranged from 12 to 93 days, with a total of 146 tracking days (mean ± 1 SD = 48.7 ± 40.7 days). We observed mean individual radio-tracked python home ranges of 22.5 km 2 (2250 ha) with overall low site fidelity; all home ranges were within the park boundary. Python core-use areas included slough and coastal habitat types, and we delineated 18 common-use areas (that is, areas where individual core-use areas spatially overlapped). Tree islands were a principal feature of common-use areas, even if they were not the predominant habitat type. Multiple common-use areas were in proximity to roads. The longest movements of individual pythons correlated well with presence of surface water, and occurred during both wet and dry seasons. Conclusions: High-use areas determined from python habitat-use and movement data may be optimal locations for targeted control efforts and further studies on impacts to native fauna.

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

“…Among squamates, only large lizards such as blue-tongue skinks and monitor lizards have been tracked using GPS tags [e.g., 16,17]. Hart et al [18] reported on the first preliminary application of GPS technology in a large constrictor, the Burmese python (Python bivitattus). This was the first documented GPS application in any snake.…”

“…Many large constrictors are considered threatened or declining in their native range [20][21][22], whereas other species have become invasive [23], and management of both invasive and imperiled large constrictors would benefit from an improved understanding of their spatial ecology. VHF telemetry has been used to study large constrictor behavior and ecology around the world, including studies on a variety of taxa (e.g., pythons, boas, and anacondas) in a number of different countries (e.g., Argentina, Australia, Bangladesh, South Africa, USA, and Venezuela) [18,[24][25][26][27][28][29][30]. Many of these VHF studies yielded infrequent, irregularly timed, and predominantly daytime locations, and increasing the frequency and regularity of VHF locations in studies of snakes is often difficult due to logistical constraints (e.g., long time to manually record a VHF fix, workload, site inaccessibility, safety-particularly when tracking at night, etc.)…”

“…GPS signal attenuates under the skin, and therefore, these tags must have an external antenna that exits through the skin, potentially compromising the animal's health and tag retention. Moreover, many large constrictors have been shown to select habitats with thick vegetation cover [18,20,32,33], which is likely to reduce GPS fix rates [8]. Furthermore, some large constrictors often spend time in water and can tolerate high salinities [34], further increasing the likelihood of signal loss [5].…”

“…Burmese pythons have likely been established and breeding in ENP since the mid-1980s [35]. Their remarkable crypsis makes them impossible to study by direct observation [36], so most of what we know about their movement patterns and habitat selection is based on VHF radio tracking in ENP [18,32,37]. Due to the logistical difficulties of working in the vast Everglades landscape, VHF tracking has typically been limited to one location/animal/week, obtained during daylight hours, severely limiting the inferences that can be drawn about python spatial ecology.…”

“…To deal with this issue, we used the loop of non-absorbable suture (described above) to anchor the GPS tag to the muscle surrounding the python's rib cage, thereby reducing the pressure the tag could place on the antenna exit site. The VHF tag was implanted entirely subcutaneously, following standard methods, and was not anchored internally to the rib cage [18,31,42,43]. All external surgical openings were closed using both non-absorbable suture and surgical glue to reduce the possibility of any wound opening or infection.…”