Modeling the relationship between habitat preferences and home-range size: a case study on a large mobile colubrid snake from North America

Scale-dependent effects of roadways on the movement behavior of a large-bodied pit viper (Crotalus horridus)

Roadways are among the most widespread and disruptive anthropogenic land use features that influence the behavior and movement of wildlife. Negative impacts of roadways have been well documented, but the behavioral impact of roadways on smaller, cryptic species has yet to be thoroughly examined. Using a novel integration of radio telemetry and tri-axial accelerometry, we evaluated the effects of roadways on the movement behavior of 26 adult Timber Rattlesnakes (Crotalus horridus) at coarse and fine time scales in central Georgia between June 2020 and November 2021. To interpret the effect of roads at a coarse time scale, we modeled the effect of mean annual distance to roadways (DTR) on annual measures of movement and space use by C. horridus using both radio telemetry and accelerometry derived metrics (RT and ACT metrics). To explore the fine-scale impact of roadways, we quantified RT and ACT metrics during confirmed road interactions (i.e., instances when individual snakes crossed a road or encountered a road but did not cross) and compared these instances to the RT and ACT metrics calculated across the remainder of the active season within this subset of snakes. Relating the annual RT and ACT metrics to DTR revealed no significant associations at a coarse time scale. However, the evaluation of C. horridus movement behavior during punctuated road encounters revealed that snakes increased RT and ACT metrics during the road interactions compared to metrics calculated across the remainder of the active season. This might indicate that the abundance of contiguous habitat adjacent to roadways at our study site is serving as an adequate buffer to any long-term shifts in movement behavior, but the potential hidden cost of increasing movement when snakes encounter roads could have negative implications for populations that encounter roads more frequently, even in the absence of significant direct road mortality. Overall, integrating radio telemetry and accelerometry and adopting a scale-dependent approach to quantifying movement allowed for a more detailed evaluation of the response of C. horridus to roadways. This approach holds promise for detecting and interpreting previously overlooked short-term alterations in snake movement behavior with potentially significant fitness consequences.

No room to roam: King Cobras reduce movement in agriculture

BACKGROUND

Studying animal movement provides insights into how animals react to land-use changes. As agriculture expands, we can use animal movement to examine how animals change their behaviour in response. Recent reviews show a tendency for mammalian species to reduce movements in response to increased human landscape modification, but reptile movements have not been as extensively studied.

METHODS

We examined movements of a large reptilian predator, the King Cobra (Ophiophagus hannah), in Northeast Thailand. We used a consistent regime of radio telemetry tracking to document movements across protected forest and adjacent agricultural areas. Using dynamic Brownian Bridge Movement Model derived motion variance, Integrated Step-Selection Functions, and metrics of site reuse, we examined how King Cobra movements changed in agricultural areas.

RESULTS

Motion variance values indicated that King Cobra movements increased in forested areas and tended to decrease in agricultural areas. Our Integrated Step-Selection Functions revealed that when moving in agricultural areas King Cobras restricted their movements to remain within vegetated semi-natural areas, often located along the banks of irrigation canals. Site reuse metrics of residency time and number of revisits appeared unaffected by distance to landscape features (forests, semi-natural areas, settlements, water bodies, and roads). Neither motion variance nor reuse metrics were consistently affected by the presence of threatening landscape features (e.g. roads, human settlements), suggesting that King Cobras will remain in close proximity to threats, provided habitat patches are available.

CONCLUSIONS

Although King Cobras displayed individual heterogeneity in their response to agricultural landscapes, the overall trend suggested reduced movements when faced with fragmented habitat patches embedded in an otherwise inhospitable land-use matrix. Movement reductions are consistent with findings for mammals and forest specialist species.

A paradigm for information needed to protect at-risk species: northern pine snake (Pituophis melanoleucus) in the pine barrens as a case study

New methods of examining the risk to endangered, threatened and rare species are required to identify vulnerability. A paradigm for examining risk is presented that describes anthropogenic threats, species activities, and vulnerabilities, and uses Northern pine snakes (Pituophis melanoleucus) in the New Jersey Pine Barrens as a case study. The paradigm includes (1) conceptual model of natural, anthropogenic, and interactive stressors, (2) template of the functional attributes of threats from human activities, and (3) template of effects from different human activities. Pine snake behavior throughout the year was used to examine the temporal overlap in high snake vulnerability periods and desired human activities in a shared habitat. New data on autumn behavior of pine snakes are also provided. Passive integrated transponders (PIT tag) tracking technology indicated that the fall basking activity period is both longer in duration, and at a higher intensity than previously presumed. During the autumn, individual snakes moved in and out of dens an average of 6 times over a two-month period. Younger snakes at a small hibernaculum were more active than those at hibernacula with larger and older snakes. The high activity period of pine snakes overlaps with the timing of preferred off-road-vehicle (ORV) use, controlled burns, and other human activities, increasing snake vulnerability, potentially causing behavioral disruptions, injury, and death. The conceptual model illustrating relationships between attributes of human activity and effects may be utilized to determine risks to other listed species, and those of special concern in different habitats. This paradigm also provides managers with template tools to assess risks to species that may also be used to provide information to the public.

Wolves adapt territory size, not pack size to local habitat quality

1. Although local variation in territorial predator density is often correlated with habitat quality, the causal mechanism underlying this frequently observed association is poorly understood and could stem from facultative adjustment in either group size or territory size. 2. To test between these alternative hypotheses, we used a novel statistical framework to construct a winter population-level utilization distribution for wolves (Canis lupus) in northern Ontario, which we then linked to a suite of environmental variables to determine factors influencing wolf space use. Next, we compared habitat quality metrics emerging from this analysis as well as an independent measure of prey abundance, with pack size and territory size to investigate which hypothesis was most supported by the data. 3. We show that wolf space use patterns were concentrated near deciduous, mixed deciduous/coniferous and disturbed forest stands favoured by moose (Alces alces), the predominant prey species in the diet of wolves in northern Ontario, and in proximity to linear corridors, including shorelines and road networks remaining from commercial forestry activities. 4. We then demonstrate that landscape metrics of wolf habitat quality - projected wolf use, probability of moose occupancy and proportion of preferred land cover classes - were inversely related to territory size but unrelated to pack size. 5. These results suggest that wolves in boreal ecosystems alter territory size, but not pack size, in response to local variation in habitat quality. This could be an adaptive strategy to balance trade-offs between territorial defence costs and energetic gains due to resource acquisition. That pack size was not responsive to habitat quality suggests that variation in group size is influenced by other factors such as intraspecific competition between wolf packs.

Small reserves around hibernation sites may not adequately protect mobile snakes: the example of Great Basin Gophersnakes (Pituophis catenifer deserticola) in British Columbia

A common strategy for reptile conservation is to establish reserves around nesting or hibernation sites. The government of British Columbia, Canada, mandates protection of 200–300 ha wildlife habitat areas (WHAs) around hibernation sites of the federally threatened Great Basin Gophersnakes ( Pituophis catenifer deserticola Stejneger, 1893), but practical constraints result in a mean size of 193 ha. To evaluate the efficacy of this reserve size, we radio-tracked 39 adult Gophersnakes at four study sites in the Okanagan Valley in 2006 and 2007. Home ranges averaged 10.5 ± 1.7 ha. The maximum distance traveled from a hibernation site was 2400 m, whereas the maximum distance dispersed averaged 520 ± 65 m. An idealized circular WHA of 193 ha with the hibernation site at the centre would be large enough to contain Gophersnake home ranges, but the dispersal data show that only 85% of snakes would stay within that area. Small or asymmetrical WHAs likely protect even fewer Gophersnake locations. We recommend that WHAs be expanded if possible because the high mobility of Gophersnakes suggests that current reserves may not offer adequate protection.