Short-Term Space-Use Patterns of Translocated Mojave Desert Tortoise in Southern California.

Increasingly, renewable energy comprises a larger share of global energy production. Across the western United States, public lands are being developed to support renewable energy production. Where there are conflicts with threatened or endangered species, translocation can be used in an attempt to mitigate negative effects. For the threatened Mojave desert tortoise (Gopherus agassizii), we sought to compare habitat- and space-use patterns between short-distance translocated, resident, and control groups. We tested for differences in home range size based on utilization distributions and used linear mixed-effects models to compare space-use intensity, while controlling for demographic and environmental variables. In addition, we examined mean movement distances as well as home range overlap between years and for male and female tortoises in each study group. During the first active season post-translocation, home range size was greater and space-use intensity was lower for translocated tortoises than resident and control groups. These patterns were not present in the second season. In both years, there was no difference in home range size or space-use intensity between control and resident groups. Translocation typically resulted in one active season of questing followed by a second active season characterized by space-use patterns that were indistinguishable from control tortoises. Across both years, the number of times a tortoise was found in a burrow was positively related to greater space-use intensity. Minimizing the time required for translocated tortoises to exhibit patterns similar to non-translocated individuals may have strong implications for conservation by reducing exposure to adverse environmental conditions and predation. With ongoing development, our results can be used to guide future efforts aimed at understanding how translocation strategies influence patterns of animal space use

Summary of multiple comparisons <i>Z-</i>tests of pairwise differences (Estimate) in mean log-UD (i.e., log-hectares encompassed by the 95% kernel density estimate) among the four tortoise study groups, including standard errors (SE), test statistics (<i>z</i>-value), and adjusted <i>p</i>-values for the 2012 and 2013 active seasons.

<p>CW = control west; CE = control east; RE = resident; TR = translocated. Significant differences were detected between the translocated group and each of other groups in the 2012 active season; no other statistically significant differences were detected.</p><p>Summary of multiple comparisons <i>Z-</i>tests of pairwise differences (Estimate) in mean log-UD (i.e., log-hectares encompassed by the 95% kernel density estimate) among the four tortoise study groups, including standard errors (SE), test statistics (<i>z</i>-value), and adjusted <i>p</i>-values for the 2012 and 2013 active seasons.</p

Location of the study area in the Ivanpah Valley of southern California, USA.

<p>The Ivanpah Solar Electric Generating System project footprint (white boundary), as well as the locations of the translocated and resident (yellow area), control west (orange), and control east (beige) study groups also are shown.</p

Model-averaged parameter estimates (β¯~) unconditional standard errors (SE), 95% confidence intervals (CI), and cumulative Akaike’s Information Criterion weights (w₊(<i>j</i>)) for all variables used to model space-use intensity in the combined 2012 and 2013 active seasons.

<p>MCLavg = average midline carapace length in each year. In our design matrix, the categorical variables were specified such that control west, female, and 2012 were the baseline contrasts used for comparison in the study group, sex, and year categories, respectively. Note the negative effect for translocated and positive effect for year × translocated, suggesting that space-use intensity increased for translocated tortoises in 2013 relative to 2012.</p><p>Model-averaged parameter estimates (<math><mrow><mrow><mi>β</mi><mo stretchy="true">¯</mo></mrow><mo>~</mo></mrow></math>) unconditional standard errors (SE), 95% confidence intervals (CI), and cumulative Akaike’s Information Criterion weights (w₊(<i>j</i>)) for all variables used to model space-use intensity in the combined 2012 and 2013 active seasons.</p

Estimates of mean percentage overlap of 95% utilization distributions between resident and translocated male and female tortoises monitored during the 2012 and 2013 active seasons combined (approximately April through October).

<p>TT = overlap between tortoises in the translocated study group, RR = overlap between tortoises in the resident study group, and TR = overlap between tortoises in the translocated study group with those in the resident group. Grey bars represent overlap of males with other males and white bars show the percentage of overlap between females. Note that males in all comparisons had greater overlap than did females and those tortoises in the translocated study group had greater overlap for both sexes than in the other comparisons.</p

Example utilization distribution (spatial extent) and 95% kernel density estimate (height and coloration), as a metric of space-use intensity, for a control west (left two panels) and translocated (right two panels) tortoise monitored during the 2012 active season (approximately April through October).

<p>The control west individuals exhibited greater space-use intensity than translocated tortoises, which is reflected in the higher peaks and more limited spatial extent associated with the control west tortoise’s utilization distribution.</p

Number and composition of individual tortoises in each study group during the 2012 and 2013 active seasons, partitioned by average midline carapace length (MCL, in millimeters), MCL standard error (SE_MCL), average utilization distribution (UD, in hectares) and UD standard error (SE_UD).

<p>¹The UD is defined as the area encompassed by the 95% kernel density estimate for each tortoise.</p><p>Number and composition of individual tortoises in each study group during the 2012 and 2013 active seasons, partitioned by average midline carapace length (MCL, in millimeters), MCL standard error (SE_MCL), average utilization distribution (UD, in hectares) and UD standard error (SE_UD).</p

Estimates of mean percentage overlap of 95% utilization distributions between resident and translocated tortoises monitored during the 2012 (grey bars) and 2013 (white bars) active seasons (approximately April through October).

<p>TT = overlap between tortoises in the translocated study group, RR = overlap between tortoises in the resident study group, and TR = overlap between tortoises in the translocated study group with those in the resident group. Note that overlap between translocated study group individuals was more than twice as great in 2012 compared to 2013.</p

Summary of multiple comparisons <i>Z-</i>tests of pairwise differences (Estimate) in mean log-UD (log-hectares encompassed by the 95% kernel density estimate) among the sexes, including standard errors (SE), test statistics (<i>z</i>-value), and adjusted <i>p</i>-values for the 2012 and 2013 active seasons.

<p>F = Female; M = Male; U = Unknown.</p><p>Summary of multiple comparisons <i>Z-</i>tests of pairwise differences (Estimate) in mean log-UD (log-hectares encompassed by the 95% kernel density estimate) among the sexes, including standard errors (SE), test statistics (<i>z</i>-value), and adjusted <i>p</i>-values for the 2012 and 2013 active seasons.</p