Maximal Running Speeds of Bipedal and Quadrupedal Rodents

A s s ~ ~ ~ c ~ . M a x i m a l running speeds of both bipedal (Dipodom ys, Microdipodops) and quadrupedal (Chaetodipus, Perognathus) heteromyid rodents, and some sympatric nocturnal cricetids and diurnal sciurids, were measured in the laboratory (17 species, 131 individuals) and in the field (eight species, 138 individuals). We found significant, repeatable differences among individuals within species. Significant differences also were found among species: Perognathus longimembris (8.9 g, 9.9 km/h) and Onychomys torridus (19.3 g, 10.3 km/h) were relatively slow; Microdipodops megacephalus (12.3 g, 10.9 km/h) and Peromyscus crinitus (13.7 g, 11.4 km/h) were somewhat faster; Chaetodipus baileyi (39.1 g, 12.4 km/h), Perognathus parvus (24.4 g, 12.5 km/h), Chaetodipus fallax (18.0 g, 12.8 km/h), Peromyscus eremicus (19.8 g, 13.1 km/h), and Peromyscus maniculatus (18.2 g, 13.4 km/h) attained similar speeds; Peromyscus truei (19.3 g, 14.3 km/h) was faster still; Neotoma lepida (110.6 g, 17.1 km/h) and three squirrel species were the fastest tested in the laboratory. Kangaroo rats (Dipodomys) did not exert themselves maximally in the laboratory, but attained speeds significantly higher than pocket mice (Chaetodipus, Perognathus) or other sympatric rodents in the field. In addition, Dipodomys displayed erratic escape behavior (zig-zagging) when pursued in the field significantly more frequently than Chaetodipus or Perognathus. Higher sprint speeds and erratic escape behavior may allow kangaroo rats to escape from some predators (e.g., raptors, canids), and hence exploit open microhabitats (of presumed higher predation risk) to a greater extent than slower sympatric rodents.