Department of Biological Sciences, University of New Hampshire, United States
Background/Question/Methods
Homing behavior has been widely studied across vertebrates, particularly among non-territorial species that navigate by flying or swimming. Compared to other groups, our understanding of the spatial cognitive abilities of lizards is limited, particularly for territorial, arboreal species inhabiting dense forests. Here we report the homing abilities of Anolis gundlachi, a highly territorial, arboreal lizard native to the tropical forests of Puerto Rico. We first evaluated the homing ability of male and female A. gundlachi by displaying them, without access to familiar landmarks or goal-emanating cues, to distances of 40 or 80 meters from their original perches, which is well beyond their territory size. We then used computer simulations to test the possibility that homing could be achieved by randomly walking through the habitat. Finally, we took advantage of the recent miniaturization of tracking devices to perform an additional series of displacement experiments to document the detailed paths used by the lizards, as well as their orientation success.
Results/Conclusions
Both males and females were able to return to their home perches following displacing. Female homing frequency from 40 m = 0.45, whereas male homing frequency from 40m = 0.80 and from 80m = 0.60. Males that homed did so, on average, in 1.88 ± 0.42 days (range = 1–5), while females took 3.44 ± 0.77 days (range = 1–8). Results of telemetry experiments show that lizards were clustered around the homeward bearing at the end of the study (mean = 352.5°, r = 0.595, p = 0.003, Rayleigh test of uniformity). Furthermore, random-walk simulations reject the possibility that homing success resulted from this strategy. In fact, not a single simulation trial (10,000 trials per distance) produced return rates as high as those we observed. We suggest that A. gundlachi is using "map"-like information at the release site to determine its location relative to home, and potentially a "compass-sense" to orient homewards. Finally, it is counterintuitive that a species like A. gundlachi, which is known as highly territorial, shows homing abilities with the degree of effectiveness reported here. One possibility is that homing ability is an incidental byproduct of selection favoring high spatial awareness in the context of territoriality.
