Sylvilagus audubonii (desert cottontail) and Lepus californicus (black-tailed jackrabbit) occur in sympatry in the southwestern United States and northern Mexico. During the daytime, both species occupy shallow excavations under shrubs known as forms. Comparisons of form and shrub characteristics between the 2 species can provide insights into connections between body size, physiology, and behavior. I examined forms of the 2 species in the Chihuahuan Desert in southern New Mexico, USA, from 2014 to 2016. In response to temperature, S. audubonii varied the structure of its forms and dug burrows, whereas L. californicus did not. Sylvilagus audubonii forms were most commonly located in the centers of patches of shrubs, whereas L. californicus forms were most commonly on the edges of patches. Overhead canopy depth and exposure to direct sunlight were not different between the 2 species, but canopy heights were less at S. audubonii forms than at L. californicus forms. Sylvilagus audubonii individuals were less visible to predators than L. californicus individuals at predator eye level in all directions, and the horizontal extent of canopies was greater at S. audubonii forms than at L. californicus forms in all directions except to the left side. An asymmetry was evident in the exposure of S. audubonii to predators, which may be the result of brain lateralization. Although distance to nearest neighbor shrubs was not different between the 2 species, open space around L. californicus forms was greater than around S. audubonii forms. Lepus californicus forms were located under Larrea tridentata in proportion to its availability and more often than forms of S. audubonii, which were located under L. tridentata less often than it was available. These observations are consistent with concordant ensembles of adaptations in which S. audubonii is smaller, more sensitive to heat, and more inclined to hide rather than run from predators in comparison with L. californicus.
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Vol. 79 • No. 2