Tenrecs

SLEEPY TROPICAL VISITOR

Tenrecs are found only in Madagascar, an island lying roughly between 12 and 25 degrees south latitude in the Indian Ocean, not far south of the equator. So tenrecs are tropical animals, not in need of hibernation. All the same, many tropical animals escape the extreme heat by a kind of sleep which is similar to hibernation but receives the name 'aestivation'.

The temperature in the tenrec's native country seldom falls below 60°F. A tenrec taken to Paris hibernated on cool days in summer when the temperature dropped below 50°F. This gives us a possible clue to the origin of the seasonal habit of hibernating. As we look around the animals of the world we find that they vary in their temperature-tolerance. Some can tolerate wide extremes of temperature, others can tolerate only narrow degrees of temperature change. Those living in hot countries that cannot tolerate high temperatures estivate. Those in cold temperatures will habitually hibernate, or else they go into states that are variously described as torpor, dormancy or winter rigidity.

This prompts some scientists to suggest that true hibernation is found in species whose ancestors were originally tropical but migrated north. In doing so their tendency to sleep or become dormant during cold spells came, in the course of time, to be a seasonal rhythm, so that the onset of hard weather is anticipated by internal changes, in an orderly preparation for hibernation.