Spatial and population ecology of Kinosternon stejnegeri on the border of Arizona, United States, and Sonora, Mexico.

We studied the population size, demography, seasonal ecology, and movements of Arizona Mud Turtles (Kinosternon stejnegeri) in 2 earthen stock tanks on the U.S.-Mexico international border in Pima County, Arizona. Using closed-population models within year, we estimated the population in the "West Tank" to number 50 individuals (95% CI 42 to 65) in 2011 and 74 individuals (95% CI 62 to 96) in 2019. Using open-population models to fit capture-recapture data from 2011, 2018, and 2019, we estimated the population in the West Tank in 2018 to be 63 turtles. We estimated that 35 (95% CI 24 to 72) of 41 turtles (84.6%) captured in 2011 were still surviving in the West Tank in 2019, yielding an average annual survivorship rate of 0.98. The overall size-class distribution changed significantly from 2011 to 2019, with a shift from juvenile age classes to larger adults. In 2011, twenty-three out of 41 turtles (56.1%) were smaller than 90 mm carapace length (SCL). By 2019, only 5 out of 53 turtles (9.4%) were smaller than 90 mm SCL. Conversely in 2011, only 1 out of 41 turtles (2.4%) was larger than 170 mm SCL, while in 2019, 7 out of 53 turtles (13.2%) were larger than 170 mm SCL, suggesting that the mean age of the population increased during this time. Arizona Mud Turtles that were radio-tracked in at least 2 full years (2017 and 2018) had home range axes ranging from 59 to 782 m (average axis = 357.5 m, median axis = 241.0 m). Turtles tracked in both years traveled minimum overland distances of 33 to 533 m from their tank-of-capture origin to either an upland activity area or to another tank (average max distance = 261 m, median max distance = 185 m). Three turtles of 11 tracked in both years (2M, 1F; 27.3%) spent portions of the summer and fall on the Mexico side of the border fence. Two turtles crossed in both years and one in only one year. Most aquatic locations (97.2%) were in anthropogenic tanks. We found that 62.7% of overwintering locations were in burrows of banner-tailed kangaroo rats (Dipodomys spectabilis). Eight of 11 turtles (72.7%) used 12 distinct Dipodomys burrow complexes. One of the 12 overwintering burrow complexes was destroyed by a U.S. Border Patrol construction yard following the completion of this study. Though apparently stable in recent decades, this significant population on protected federal land appears to be small and vulnerable to development in the vicinity of the U.S.-Mexico border. This work is the first major spatial ecology study of K. stejnegeri and provides valuable information on the ecology and movements of this poorly studied species. [ABSTRACT FROM AUTHOR]