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

Comparing acoustic and satellite telemetry: an analysis quantifying the space use of Chelonia mydas in Bimini, Bahamas

Passive acoustic and Argos satellite telemetry are common methods for tracking marine species and are often used similarly to quantify space use. However, data-driven comparisons of these methods and their associated ecological inferences are limited. To address this, we compared temporal durations, spatial resolutions, financial costs and estimates of occurrence and range distributions for each tracking approach using nine juvenile green turtles (Chelonia mydas) in Bimini, Bahamas. Tracking durations were similar, although acoustic tracking provided higher spatiotemporal resolution than satellite tracking. Occurrence distributions (95%) estimated from satellite telemetry were 12 times larger than those from acoustic telemetry, while satellite range distributions (95%) were 89 times larger. While individuals generally remained within the extent of the acoustic receiver array, gaps in coverage were identified. These gaps, combined with the lower accuracy of satellite telemetry, were likely drivers for the larger satellite distributions. Costs differed between telemetry methods, with acoustic telemetry being less expensive at larger sample sizes with a previously established array. Our results suggest that acoustic and satellite telemetry may not provide similar inferences of individual space use. As such, we provide recommendations to identify telemetry methods appropriate for specific study objectives and provide discussion on the biases of each.

Spatial Ecology of an Arboreal Iguana (Oplurus cyclurus) in a Treeless Landscape

Understanding the spatial ecology of species has important implications for conservation, as it helps identify suitable habitats and minimum requirements for biodiversity monitoring and management. The spiny-tailed lizard Oplurus cyclurus is a widespread endemic iguanid occurring in dry areas of southern and western Madagascar. While the species is known to be mostly arboreal, populations of the Isalo sandstone massif suggest local adaptation to a less forested savannah and a more exposed habitat. We radio-tracked 19 spiny-tailed lizards to investigate the species' rock-dwelling behaviour and spatial ecology at Isalo National Park. Tracked individuals showed high site and burrow fidelity, and a basking behaviour mostly tied to the accessibility of their burrow, the time of day, and their life stage. Activity peaked during the sunniest hours, while juveniles were more active than adults with unfavourable weather conditions. Despite high burrow fidelity, lizards used shelters non-exclusively, regularly changing (approx. once a week) with neighbouring burrows (average distance between burrows = 13.6 m). However, there was no obvious relation between lizards' body and/or tail size and the width and depth of selected burrows. Dynamic Brownian Bridge Movement Models estimated frequented areas over 247.8 m2 (95% isopleth), where territorial overlap is common. Our results challenge the notion that burrow-site fidelity is the sole driving factor behind space utilization in the studied population. We argue that the apparently unusual saxicolous habits imposed by habitat features (the absence of trees) may lead to local behavioural adjustments influencing antipredatory and foraging strategies, as well as intraspecific interactions.

Residency and space use estimation methods based on passive acoustic telemetry data

Acoustic telemetry has helped overcome many of the challenges faced when studying the movement ecology of aquatic species, allowing to obtain unprecedented amounts of data. This has made it into one of the most widely used methods nowadays. Many ways to analyse acoustic telemetry data have been made available and deciding on how to analyse the data requires considering the type of research objectives, relevant properties of the data (e.g., resolution, study design, equipment), habits of the study species, researcher experience, among others. To ease this decision process, here we showcase (1) some of the methods used to estimate pseudo-positions and positions from raw acoustic telemetry data, (2) methods to estimate residency and (3) methods to estimate two-dimensional home and occurrence range using geometric or hull-based methods and density-distribution methods, a network-based approach, and three-dimensional methods. We provide examples of some of these were tested using a sample of real data. With this we intend to provide the necessary background for the selection of the method(s) that better fit specific research objectives when using acoustic telemetry.

Movement Patterns of Roaming Companion Cats in Denmark—A Study Based on GPS Tracking

We studied the roaming patterns of companion cats in Denmark. The movements of 97 cats with outdoor access were traced for about seven days using GPS tracking. Data on the cats were gathered from their owners. The median time cats spent away from their homes was 5 h per day (IQR: 2.5 to 8.8 h), median daily distance moved was 2.4 km (IQR: 1.3 to 3.7 km), and median for 95% BBKDE home range was 5 ha (IQR: 2.9 to 8.5 ha). Cats above seven years of age spent less time away from home, were less active and had a smaller home range than younger cats. Cats with access to nature areas spent more time away from home, were more active and had larger home ranges. Intact male cats spent more time away from home than neutered cats and had larger home ranges as well. Finally, rainfall had an impact on the distance moved by cats: on days without rainfall the cats moved 3.6 km on average (95% CI: 2.8; 4.5 km); and on days with heavy rainfall the cats moved 2.4 km on average (95% CI: 1.6; 3.5 km).

Malayan kraits (Bungarus candidus) show affinity to anthropogenic structures in a human dominated landscape

Animal movement can impact human–wildlife conflict by influencing encounter and detection rates. We assess the movement and space use of the highly venomous and medically important Malayan krait (Bungarus candidus) on a suburban university campus. We radio-tracked 14 kraits for an average of 114 days (min: 19, max: 218), during which we located individuals an average of 106 times (min: 21, max: 229) each. Most individuals displayed some level of attraction to buildings (n = 10) and natural areas (n = 12); we identified a similar unambiguous pattern of attraction to buildings and natural areas at the population level (of our sample). Snakes remained in shelter sites for long durations (max: 94 days) and revisited sites on average every 15.45 days. Over 50% of locations were within human settlements and 37.1% were associated with buildings. We found generally seasonal patterns of activity, with higher activity in wet seasons, and lower activity in the hot season. These results show frequent proximity between Malayan kraits and humans at the university; thereby, suggesting a near constant potential for human-wildlife conflict. Despite the fact that no snakebites from this species occurred at the university during our study period, substantial education and awareness training should be considered to ensure continued coexistence on campus.

Spatial ecology, activity patterns, and habitat use by giant pythons (Simalia amethistina) in tropical Australia

Although giant snakes are abundant in some tropical forests, their ecology is far less well-known than for smaller species of snakes in cooler climates. Information on spatial ecology can clarify management issues such as the sizes and types of habitats needed for conservation. We radio-tracked 27 scrub pythons (Simalia amethistina; snout-vent lengths 2.02 to 3.70 m) in Cape York, near the northeastern tip of Australia, for a mean period of 426 days (up to 1001 days) per snake. Home ranges were larger in males than females (means 0.60 vs. 0.28 km²) and overlapped considerably among individuals. All snakes used rainforest habitat, but seasonal shifts into open woodland were common. Snakes were active primarily by night, with larger snakes hunting less of the time overall, and more often by day. Hunting behaviour was seen more often during the wet season than the dry season. Average daily displacement was < 10 m, typically involving a shift from diurnal refuge to nocturnal ambush-site. A reliance on sit-and-wait predation results in small home ranges and limited movements, despite the large body size of this species.

Long-Distance Movements of Feral Cats in Semi-Arid South Australia and Implications for Conservation Management

Simple Summary

To efficiently control invasive animals, it is vital to have knowledge about their behaviour, their movements and how they use the landscape. Unusual behaviour is normally excluded from datasets, as it is considered to be an outlier that may distort analyses. In our study, we present movement data from feral cats in the arid and semi-arid zones of Australia. Feral cats are a serious problem to the native wildlife of Australia and in many parts of the world. Cats are known to show fidelity to geographic areas and may defend them against other cats. Until now, research has focused on these areas, home ranges or territories, that feral cats need to survive and reproduce. We argue that a part of their movement behaviour, large journeys away from the area they normally use, has been overlooked and has been considered to be unusual behaviour. We explain why we think that this is the case and present examples from other studies additional to our data set to show that these long-distance movements are a regular occurrence. To achieve a better protection of native wildlife from predation by feral cats, we believe that these long-distance movements should be considered as part of the normal behaviour of feral cats when planning cat control operations.

Abstract

Movements that extend beyond the usual space use of an animal have been documented in a range of species and are particularly prevalent in arid areas. We present long-distance movement data on five feral cats (Felis catus) GPS/VHF-collared during two different research projects in arid and semi-arid Australia. We compare these movements with data from other feral cat studies. Over a study period of three months in the Ikara-Flinders Ranges National Park, 4 out of 19 collared cats moved to sites that were 31, 41, 53 and 86 km away. Three of the cats were males, one female; their weight was between 2.1 and 4.1 kg. Two of the cats returned to the area of capture after three and six weeks. During the other study at Arid Recovery, one collared male cat (2.5 kg) was relocated after two years at a distance of 369 km from the area of collar deployment to the relocation area. The movements occurred following three years of record low rainfall. Our results build on the knowledge base of long-distance movements of feral cats reported at arid study sites and support the assertion that landscape-scale cat control programs in arid and semi-arid areas need to be of a sufficiently large scale to avoid rapid reinvasion and to effectively reduce cat density. Locally, cat control strategies need to be adjusted to improve coverage of areas highly used by cats to increase the efficiency of control operations.

Lots of movement, little progress: a review of reptile home range literature

Reptiles are the most species-rich terrestrial vertebrate group with a broad diversity of life history traits. Biotelemetry is an essential methodology for studying reptiles as it compensates for several limitations when studying their natural history. We evaluated trends in terrestrial reptile spatial ecology studies focusing upon quantifying home ranges for the past twenty years. We assessed 290 English-language reptile home range studies published from 2000-2019 via a structured literature review investigating publications' study location, taxonomic group, methodology, reporting, and analytical techniques. Substantial biases remain in both location and taxonomic groups in the literature, with nearly half of all studies (45%) originating from the USA. Snakes were most often studied, and crocodiles were least often studied, while testudines tended to have the greatest within study sample sizes. More than half of all studies lacked critical methodological details, limiting the number of studies for inclusion in future meta-analyses (55% of studies lacked information on individual tracking durations, and 51% lacked sufficient information on the number of times researchers recorded positions). Studies continue to rely on outdated methods to quantify space-use (including Minimum Convex Polygons and Kernel Density Estimators), often failing to report subtleties regarding decisions that have substantial impact on home range area estimates. Moving forward researchers can select a suite of appropriate analytical techniques tailored to their research question (dynamic Brownian Bridge Movement Models for within sample interpolation, and autocorrelated Kernel Density Estimators for beyond sample extrapolation). Only 1.4% of all evaluated studies linked to available and usable telemetry data, further hindering scientific consensus. We ultimately implore herpetologists to adopt transparent reporting practices and make liberal use of open data platforms to maximize progress in the field of reptile spatial ecology.

Native Burmese pythons exhibit site fidelity and preference for aquatic habitats in an agricultural mosaic

Animal movement and resource use are tightly linked. Investigating these links to understand how animals use space and select habitats is especially relevant in areas affected by habitat fragmentation and agricultural conversion. We set out to explore the space use and habitat selection of Burmese pythons (Python bivittatus) in a heterogenous, agricultural landscape within the Sakaerat Biosphere Reserve, northeast Thailand. We used VHF telemetry to record the daily locations of seven Burmese pythons and created dynamic Brownian Bridge Movement Models to produce occurrence distributions and model movement extent and temporal patterns. To explore relationships between movement and habitat selection we used integrated step selection functions at both the individual and population level. Burmese pythons had a mean 99% occurrence distribution contour of 98.97 ha (range 9.05–285.56 ha). Furthermore, our results indicated that Burmese pythons had low mean individual motion variance, indicating infrequent moves and long periods at a single location. In general, Burmese pythons restricted movement and selected aquatic habitats but did not avoid potentially dangerous land use types like human settlements. Although our sample is small, we suggest that Burmese pythons are capitalizing on human disturbed landscapes.

Going underground: short- and long-term movements may reveal the fossorial spatial ecology of an amphisbaenian

BACKGROUND

The movement and spatial ecology of an animal depends on its morphological and functional adaptations to its environment. In fossorial animals, adaptations to the underground life help to face peculiar ecological challenges, very different from those of epigeal species, but may constrain their movement ability.

METHODS

We made a long-term capture-recapture study of the strictly fossorial amphisbaenian reptile Trogonophis wiegmanni to analyze its long-term movement patterns. We also used passive integrated transponder (PIT) telemetry to detect and follow undisturbed individuals underground, obtaining data of their short-term movement patterns.

RESULTS

Amphisbaenians showed a high site fidelity, moving short distances and over small areas, and spending some days without any noticeable movement, even under favorable conditions. We also found differences in movements between sexes and age classes.

CONCLUSIONS

This movement and spatial strategy can be related to the energetic constrains of underground burrowing, or to the low metabolic requirements of fossorial reptiles, as distances and areas covered were much smaller than for epigeal reptiles of similar size. Individual differences probably reflect differential reproductive and social requirements of males and females, and that younger individuals might show more floating behavior until they can settle in a territory. This study is a rare example describing the movement ecology of a fossorial species and may contribute to the general understanding of the factors that affect space use and movement decisions in animals.