INTERSPECIFIC VARIATION IN ANTIPREDATOR BEHAVIOR IN SYMPATRIC SPECIESOF KANGAROO RAT

Kangaroo rats, Dipodomys, occupy desert habitats with little cover and thus are under high predation risk from diverse predators. The behavi or used to assess predation risk or to escape capture is unknown. We t herefore compared anti-predator behavior of two sympatric species of k angaroo rat of different sizes, D. merriami and D. spectabilis. We fir st examined whether kangaroo rats use olfaction as a first line of def ense against snake predation and tested the rats for their responses t o scent extracted from two species of snake that live sympatrically wi th the kangaroo rats, the Mojave rattlesnake (Crotalus scutulatus) and the gopher snake (Pitophis melanoleucus). We also tested for species differences in anti-predator behavior through 15-min interactions betw een the kangaroo rats and free-moving gopher snakes. We found that D. spectabilis actively approached the scent of both rattlesnakes and gop her snakes more than controls of vegetable oil and evaporated solvent (Fig. 1). In contrast, D. merriami did not differentiate snake odors f rom controls in the experimental arena, but they sniffed the sand wher e a free-moving snake had passed more than D. spectabilis. Both specie s successfully avoided predation in encounters with live snakes. Altho ugh total numbers of approaches and withdrawals were similar (Fig. 2), D. spectabilis spent significantly more time within striking distance of the snake than D. merriami. D. spectabilis approached the head of the snake in 93% of its approaches and often engaged in nose to snout contact with the snake. If the snake struck, D. spectabilis jumped dir ectly backward to avoid a strike and footdrummed at a safe distance. I n contrast, D. merriami oriented to the snake more than D. spectabilis , but approached the head in only 41% of the approaches and rarely eng aged in nose-to-snout contact. The snakes struck, hissed and decreased predatory approaches with D. spectabilis but not with D. merriami (Fi g. 3). These results show that kangaroo rats can behaviorally influenc e the risk of being preyed on by snakes. The two species differ, howev er, in how they react to snakes. The larger D. spectabilis confronts s nakes while the smaller D. merriami monitors snakes from a safe distan ce and avoids them.