Home range, seasonality, and the importance of canopy cover for Texas Tortoises (Gopherus berlandieri)
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Abstract
Texas Tortoises (Gopherus berlandieri) are understudied compared to federally protected congeners. Despite important early studies on the basic ecology of G. berlandieri, quantitative identification of habitat associations with specific environmental conditions has been limited. Gopherus berlandieri inhabits Tamaulipan thornscrub across its range, and coastal populations are historically associated with low-relief clay ridges with thick mesquital scrub surrounded by salt prairie grasslands. Our study examined tortoise home range size and association with canopy cover and potential ground moisture at a protected natural area in Cameron County, TX, USA. Twelve tortoises were outfitted with GPS loggers that recorded location once an hour from March 2020 to March 2022. To delineate home ranges, we estimated utilization distributions (UDs) for tortoises as autocorrelated kernel density estimates (AKDEs) at low-use (95%) and core-use (50%) levels for each tortoise. UDs were estimated for the entire study period and during seasons of sustained heat or cold to determine if tortoises used space differently across these seasons over the study period. Applying a use-availability study design, we compared canopy cover and potential mesic ground condition (i.e., precipitation flow accumulation) within each tortoise's UD (“use”) to the area within 1 day's movement around the boundary of the UD (“available”). Tortoise UD sizes were significantly different across seasons for low-use (95%) but not for core-use (50%) AKDE levels. Tortoise UDs had greater canopy cover compared to available-but-unused areas at both AKDE levels. Potential mesic ground condition did not significantly differ between available and used areas. Our study revealed that tortoises vary the size of their home ranges throughout the year, whereas areas of intensive use or occupation tended to remain remarkably stable throughout the year. In seasons of extreme weather (hot or cold), tortoises seem to seek out areas of denser canopy cover that likely serve as thermal refugia. Based on our results, effective habitat identification may best be served by ensuring that canopy cover is at least equivalent to the values reported here to ensure sufficient refugia during extreme seasonal temperatures.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Home range, seasonality, and the importance of canopy cover for Texas Tortoises (Gopherus berlandieri) |
| Series title | Herpetologica |
| DOI | 10.1655/Herpetologica-D-24-00045 |
| Volume | 81 |
| Issue | 3 |
| Year Published | 2025 |
| Language | English |
| Publisher | BioOne |
| Contributing office(s) | Western Ecological Research Center |
| Description | 12 p. |
| First page | 224 |
| Last page | 235 |
| Country | United States |
| State | Texas |
| County | Cameron County |
| Other Geospatial | Palo Alto Battlefield National Historical Park |