How inclines affect the escape behaviour of a dune-dwelling lizard, Uma scoparia

Although previous laboratory studies have commonly determined sprinting speeds of lizards on horizontal surfaces, the speeds and slopes used during the escapes of lizards in natural habitats with variable inclines are virtually unstudied. To quantify performance and the use of inclined surfaces during escape, we took advantage of the footprints left in soft substrate and the simple surface topography of the natural dune habitat of the Mojave fringe-toed lizard, U. scoparia. The lengths of 52 escape paths ranged from 1.7-34 m, and the inclines of I-m portions of escape paths ranged from -25 degrees to 28 degrees, which effectively encompassed the entire range of inclines in the habitat. The cumulative frequencies (N=550) of inclines along l-m intervals of the escape paths were not a simple random sample of the habitat. Less than 10% of the cumulative distance travelled during escape was bipedal, and the escape paths were relatively straight. Trajectories of the first metre of escapes were oriented significantly away from the presumed threat (observer) but were random with respect to the orientation of both the nearest cover and steepest incline. Eleven per cent of the cumulative number (N=1382) of strides measured were within 90% of the maximum stride length within each path. Multiple regressions revealed that stride lengths (and hence speed) during escapes in the field were maximized on level surfaces with no turning. For lizards tested on a level racetrack in the laboratory, maximum speeds averaged 2.8 mis (range=2.1-3.9) and approximated 75% of the maximum performance attained in the field. (C) 1998 The Association for the Study of Animal Behaviour.