Caudal luring in the southern death adder acanthophis antarcticus

-In six experiments on captive death adders (Acanthophis antarcticus), caudal movements increased in frequency when prey were nearby, and lizards (Hydrosaurus pustolosus) were attracted to the moving tail. We conclude that caudal movements of A. antarcticus serve a luring function, although they may have other functions as well. Two types of predatory caudal movements occur in death adders, those that are stimulated by prey and those that are occasionally made by snakes when no prey have been detected. The latter are conceptualized as "probes" designed to attract prey that might be out of the snake's view but still able to see the lure. e etology, Vol. 24, No. 3, p. 253-260, 1 90 0 Society for the Study of Amphibians and Reptiles i i the Southern Death A der, is a tarcticus I ,1 DONAL BOYER,2 ROBERT L E,' . Y,2 AND CHARLES W. RADCLI FE3 Psychology, Box 345, University of C lorado, Boulder, C lorado 8 309, USA , e art ent of Reptiles and Amphibians, Dallas, Texas 75260, USA , epart ent of Reptiles and Amphibians, San Diego, California 92199, USA . I six experi ents on captive death a ders (Acanthophis antarcticus), caudal movements i equency when prey were nearby, and lizards (Hydrosaurus pust lo us) w re attracted to tail. e conclude that caudal movements of A. antarcticu serve a luring function, although a e other functions as well. Two types of predatory caudal movements occur in death adders, e sti ulated by prey and those that are occasionally made by snakes whe no prey have been . latter are conceptualized as "probes" designed to attract prey that might be out of the snake's The unique appearance of the tail of Acanthophis antarcticus is well known, and tail movements have been carefully described. For example, Carpenter et al. (1978, see Figs. 1-5) reported that the tail, initially at rest near the head, first thrashed through a fairly broad arc involving 75-80% of its length; this was followed by slower waving movements involving about half of the tail and then by very slow movements involving only the tip of the tail. The number of repetitions within each phase of the display was variable, and the display could stop at any point. Therefore, in the experiments reported below we defined an episode of this behavior to have been complete when tail movements stopped for at least 3 sec. Numerous authors have speculated that a luring function is served by the tail (see summary by Cogger, 1975; McPhee, 1959; Neill, 1960; Worrell, 1963), but caution has been suggested by Greene and Campbell (1972) and Green (1973) because other interpretations are possible (see also Mertens, 1946). As far as we know, none unique ap earance of the tail of Acanhis antarcticus is well known, and tail movets have be n carefully described. For exle, Carpenter et al. (1978, see Figs. 1-5) orted that the tail, in tially at rest near the , first thrashed through a f irly broad arc olving 75-80% of its length; this was foled by slower waving movem nts involving t half of the tail and then by very slow e ents involving only the tip of the tail. number of repeti ions within each p ase t e display was variable, and the display could at any point. Ther fore, in the exp riments orted below we defined an episode of this avior to have been complete when tail e ents stop ed for at least 3 sec. erous authors have speculated tha a lurfunction is served by the tail (see summary ogger, 1975; McPhee, 1959; Neill, 1960; rel , 1963), but caution has been suggested reene and Campbell (1972) and Green (1973) ause other interpreta ions are possible (see of the non-luring interpretations described by the latter authors have been supported or refuted for death adders, although circumstantial evidence favors the luring hypothesis. For example, we observed death adders exploring a new environment, and they did not exhibit cauda movements of the sort described by Carpenter et al. (1978), even when the snakes were approached and disturbed by humans. If these tail movements serve a defensive function or if they represent nonspecific arousal, we would have expected to see them in this situation. Instead, putative luring behavior was typically seen when a snake was otherwise still, with its body arranged in an oval pattern such that the tip of the tail was positioned within a few cm of the snake's face (see Carpenter et al., 1978, fig. 1). This is sometimes called the luring posture; even if the label is premature, it points to the fact that the tail is so close to the mouth that a prey item attracted to the tail would almost certainly be within striking range (Shine, 1980). Additional circumstantial evidence has the non-luring inte pretation described by la ter authors hav been supported or reted for death adders, although circumstantial i ence favors the luring hypothesis. For exle, we observe death add rs exploring a environment, and they did not exhibit cauovements of the sort descri ed by Carter et al. (1978), ven when the snakes were roached an disturbed by humans. 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