Gulf Coast Network Inventory and Monitoring Texas Tortoise Monitoring Project

Carlson, Jane

The Texas tortoise (Gopherus berlandieri) population at Palo Alto Battlefield National Historical Park is considered as one of the park's high-priority Vital Signs --or key indicators of park ecosystem health. As such, it is the subject of long-term monitoring by the Gulf Coast Network Inventory and Monitoring Program of the National Park Service. This species is designated as threatened by the state of Texas because of documented population declines and range loss caused by habitat conversion. At the park, it is a valued faunal component of the park’s shrublands, which mainly occur on low-rising ridges called lomas. The Texas tortoise population at Palo Alto Battlefield NHP is subject to several specific threats. First, park tortoises may be geographically isolated from outside populations by ditches, roads and developed lands. Second, park tortoises may be lost to illegal collection, road mortality or predation. Third, park tortoises may be impacted by the conversion of some of the park’s shrublands into grasslands, in an effort to return park landscapes to the conditions present during the Mexican-American War in 1846. Long-term monitoring data will inform the park on how to best manage for and protect Texas tortoises and their habitats. These data will also contribute to the broader regional assessment of Texas tortoise populations across their limited geographic range. To monitor the park’s Texas tortoises, the Gulf Coast Network conducts a long-term mark-recapture study using time-and-area defined survey events that occur in the fall of each year. On seven permanent sampling units representing each of the park’s major lomas, tortoises are encountered, marked and measured, and their GPS locations are recorded. Monitoring objectives addressed by this project are: 1. To provide a detailed depiction of the status of Texas tortoises across the park’s major lomas, including catch per unit effort, within-park tortoise movements, tortoise body condition, and the distribution of sizes and sexes captured. Catch per unit effort and tortoise body condition are also analyzed for change over time. 2. To assess tortoise population parameters across the park’s major lomas and track how these parameters change over time, including estimated abundance and survivorship from mark-recapture data.

Gulf Coast Network Inventory and Monitoring Texas Tortoise Monitoring Project

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