Table 1.
Covariates employed in models of activity center movement by desert tortoises in the Ivanpah Valley, California, U.S.A., 2013–2015. All spatial covariates were calculated from values within estimated local use areas. See text and Appendix S1 in Supporting Information for additional covariate information
| Abbreviation | Description | Mean | SD | Min | Max |
|---|---|---|---|---|---|
| Temporal | |||||
| Year | Year of observation (%; 2013 = 37.9, 2014 = 32.7, 2015 = 29.4) | ||||
| Day | Tortoise encounter Julian day | 194 | 47 | 94 | 299 |
| Individual | |||||
| Area | Area of observation (%; release = 54.2, control east = 10.0, control west = 35.7) | ||||
| Sex | Sex category (%; male = 49.7, female = 42.2, subadult = 8.1) | ||||
| Translocated | Translocation status in 2012 (%; resident = 84.3, translocated = 15.7) | ||||
| MCL | Midline carapace length (cm)a | 22.9 | 42.0 | 6.7 | 31.2 |
| Density | Index of local tortoise density (n/ha)a | 0.24 | 0.43 | 0 | 6.2 |
| Landscape | |||||
| Slope | Slope of local area (°) | 2.2 | 1.7 | 0.4 | 22.3 |
| Roughness | Index of surface roughness (°; SD of slope)a | 1.2 | 0.3 | 1.0 | 3.3 |
| Wash | Area classified as wash (%) | 10.4 | 4.4 | 0.0 | 40.2 |
| Minor roads | Presence of maintained dirt roads (%; present = 14.8, absent = 85.2) | ||||
| Major roads | Presence of paved roads (%; present = 1.5, absent = 98.5) | ||||
| Fencing | Presence of barrier facility fencing (%; present = 11.0, absent = 89.0) | ||||
| Burrows | Index of burrow density (n/ha)a | 6.1 | 7.4 | 0 | 67.3 |
| Vegetation | |||||
| NDVIstart | Starting (late March) NDVIb | 0.11 | 0.01 | 0.08 | 0.19 |
| NDVIactive | Mean of April‐October NDVI | 0.11 | 0.01 | 0.08 | 0.17 |
| NDVI32 | Mean NDVI in previous 32 days | 0.11 | 0.02 | 0.07 | 0.27 |
| NDVI16 | Mean NDVI in previous 16 days | 0.11 | 0.02 | 0.07 | 0.28 |
| Shrub | Area with shrub cover (%) | 13.7 | 5.1 | 0.1 | 27.1 |
| Weather | |||||
| TmaxActive | Mean of April‐October maximum temperature (mm) | 31.2 | 1.1 | 27.6 | 32.8 |
| Tmax32 | Mean maximum temperature in previous 32 days (mm) | 32.8 | 4.0 | 22.6 | 39.8 |
| Tmax16 | Mean maximum temperature in previous 16 days (mm) | 33.4 | 4.3 | 20.3 | 41.4 |
| Rainwinter | Sum of previous November‐March precipitation (mm)b | 49.8 | 12.2 | 31.2 | 78.8 |
| Rainactive | Sum of April‐October precipitation (mm) | 68.1 | 9.7 | 43.8 | 93.4 |
| Rain32 | Sum of precipitation in previous 32 days (mm)c | 9.0 | 12.6 | 0.0 | 69.3 |
| Rain16 | Sum of precipitation in previous 16 days (mm)d | 4.2 | 7.7 | 0.0 | 59.7 |
As MCL, tortoise density, surface roughness, and burrow density differed strongly among sex category (Kruskal–Wallis χ2 ≥ 556.3, df = 2, p < .001), we took residuals from ordinary least squares models of each covariate predicted by sex category for use in models of movement.
Normalized vegetation difference index. As starting NDVI and winter precipitation differed strongly among years (Kruskal–Wallis χ2 ≥ 3,267.6, df = 2, p < .001), we took the residuals from ordinary least squares models of each covariate predicted by sex category for use in models.
Converted to a categorical covariate; low (<1 mm; 37.9% of observations), medium (≥1, <7.6 mm; 36.6%), and high (≥7.6 mm; 25.5%).
Converted to a categorical covariate; low (<1 mm; 57.1% of observations), medium (≥1, <4.5 mm; 14.7%), and high (≥4.5 mm; 28.2%).