Fauna Series No. 6

Fauna of the National Parks — No. 6 The Bighorn of Death Valley

LIFE HISTORY OF THE DEATH VALLEY BIGHORN

Home Area

We have insufficient evidence for defining the home area of a bighorn beyond the generalization that an individual sheep is born in an area containing adequate food, water, and shelter to insure survival under normal conditions. As long as the bighorn can maintain satisfactory access to these three requisites, it will probably utilize the same area all its life.

Some home areas probably include only one source of free water, others more than one. The size of the area of land involved in any one home area is inherently variable because of the great instability in the pattern of precipitation, which may allow an entire herd to subsist within an area of 4 or 5 square miles one year but require 20 square miles the next.

We know that at least a nucleus of a resident band returns to the same water source or sources year after year. For five summers we watched old Brahma, the leader at Nevares Peak, bring the same band back to water at Nevares Seeps. The water source seems to be the determining factor in the location of the home area. Loss of either food or water from either natural causes or exotic pressure would appear to be the main cause of abandonment of one area for another.

Since the bighorn is essentially gregarious, it does not claim individual territorial rights as do some animals. Some old rams appear to prefer solitude, and ewes, even the leaders of the band, will isolate themselves during lambing; but we have seen no instance of overt defense of privacy.

We have no evidence of demarcation of home areas of bands by age class or sex in this region. Bands of rams appear to occupy the same general area as ewes and lambs, with the possible exception that they may be able to range farther from water, but even this is unproven. Temporary extension of the home area is probably brought about occasionally by a ewe getting caught in a tide of rams in the rut-run and carried from one spring to another before the fervor of oestrus subsides.

Owing to their greater activity during the rut, rams probably include a greater number of water sources and therefore a greater foraging territory in their home area. However, it seems likely that the average bighorn lives and dies within 20 miles of where it was born.

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Last Modified: Thurs, May 16 2002 10:00:00 pm PDT
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