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Living on the Edge
| Article
# : |
10750 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
6 / 1993 |
1,401 Words |
| Author
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Branley Allan Branson
Branley Allan Branson is professor of biology emeritus at
Eastern Kentucky University and editor of the Transactions of
the Kentucky Academy of Science. |
Most people can recognize a toad when they encounter one. These alert, upright sitting amphibians, with their dryish, warty skins and bean-shaped glands on the sides of the head behind the eyes, can often be found hopping around in gardens or under streetlights capturing insects, returning to water for the purposes of reproduction. These are the common toads, but spade foot toads are another matter because most people have never even heard of them, much less ever seen one.
There are good reasons for this. For one, spade-foots are largely nocturnal, coming out of hiding only at nigh to feed, and often not even then. All their adaptations reflect their strong orientation to the dry land habitat where they have little competition from other members of their ilk. They spend much of their time buried in loose and or soil, where they derive moisture from the groundwater through the skin.
The hind feet of the spade-foots are provided with an enlarged spade-like structure (thus the name), which enables the toad to dig rapidly into the ground by moving the hind feet in a manner similar to that used by humans in grinding out a cigarette.
The skin of spade-foots, unlike that of true toads, is thin and moist and well supplied with a network of blood vessels that draw water from the soil in which they bury themselves. During hot, dry weather spade-foots may remain buried for weeks or months. Being nocturnal animals, their eyes strongly resemble those of a cat; the pupil is a long vertical slit. Nocturnalism is, of course, an adaptation for life in the drylands.
The burrowing habit of spade-foots is another adaptation that is of great importance in that it has allowed some spices of spade-foots to live under extremely arid conditions, such as those that prevail in the Great Basin of Utah and the Sonoran Desert.
The spade-foots mate in often exceedingly transient pools of water, and are therefore geared more to the coming of torrential downpours that to changing seasons. However, they do not emerge to breed in winter, a period when they hibernate well below the zone of freezing.
Torrential rainstorms in the Great Plains peculiar amphibians to emerge from their burrows for mating. As the rainwater fills depressions and ditches to create shallow pools, the males enter the water and, floating spread-eagled, begin their nuptial serenading. Bellowing is a more
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