Nature Publishing Group, publisher of Nature, and other science journals and reference works
my account e-alerts subscribe register
Sunday 24 September 2017
Journal Home
Current Issue
Download PDF
Export citation
Export references
Send to a friend
More articles like this

Letters to Nature
Nature 265, 235 - 236 (20 January 1977); doi:10.1038/265235a0

Mouth gaping as an effective thermoregulatory device in alligators


*Department of Biology, State University College, Buffalo, New York 14222
Department of Anatomy, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104

GAPING is a characteristic activity of several species of crocodilians in which the animal lies ashore with its mouth held open for prolonged periods1–4. It has stirred the interest of humans for millennia: gaping is depicted in Egyptian papyri and was mentioned in the writings of Herodotus and Pliny. Today interest continues in gaping and other aspects of behaviour in these large reptiles, the last of the subclass Archosauria, the group of reptiles that included the dinosaurs1,5. Gaping is a complex habit that involves variable degrees of mouth closure and sometimes includes rhythmic gular movements. Behavioural observations have suggested that gaping is a thermoregulatory response3,4 but until now physiological studies have been inconclusive. Initial reports6 stated that gaping was effective in cooling young Nile crocodiles (Crocodylus niloticus) but a recent experiment on Caiman crocodylus indicated that this behaviour had no thermoregulatory significance7. Here we present evidence from controlled laboratory and field experiments that gaping is an effective mechanism for reducing head temperatures of alligators (Alligator mississippiensis). Gaping reduced the rate of heat gain by the heads of small and large alligators when these animals were exposed to high light radiation loads at moderate air temperatures. The magnitude of this effect increased with size. Gaping had little effect on body temperature and did not reduce the final equilibrium temperature of the head.



1. Neill, W. T., The Last of the Ruling Reptiles (Columbia University, New York, 1971).
2. McIlhenny, E. A., The Alligator's Life History (Christopher, Boston, 1935).
3. Cott, H. B., Trans. zool. Soc. Lond., 29, 211–337 (1961).
4. Johnson, C. R., Comp. Biochem. Physiol., 49A, 3–28 (1974).
5. Graham, A., and Beard, P., Eyelids of Morning (A and W Visual Library, New York, 1973).
6. Cloudsley-Thompson, J. L., Br. J. Herp., 4, 107–112 (1969).
7. Diefenbach, C. O. da C., Copeia, 1975, 530–540 (1975).
8. Terpin, K. M., Dodson, P., and Spotila, J. R., Copeia, (in the press).
9. Spotila, J. R., Lommen, P. W., Bakken, G. S., and Gates, D. M., Am. Nat., 107, 391–404 (1973).
10. Smith, E. N., Physiol. Zool., 49, 37–48 (1976).
11. Gates, D. M., Energy Exchange in the Biosphere (Harper and Row, New York, 1962).
12. Spotila, J. R., and Berman, E. N., Comp. Biochem. Physiol., 55A, (in the press).
13. Grigg, G. C., and Alchin, J., Physiol. Zool., 49, 24–36 (1976).
14. Pough, F. H., and McFarland, W. N., Comp. Biochem. Physiol., 53A, 301–303 (1976).
15. Spotila, J. R., Soule, O. H., and Gates, D. M., Ecology, 53, 1094–1102 (1972).

© 1977 Nature Publishing Group
Privacy Policy