Please Eat The Daisies
KIRK ANDERSON CURATOR OF GARDENS
One of Te Living Desert’s greatest assets is its physical
surroundings - back-dropped by the grandeur of the Santa Rosa Mountains to the immediate south, rewarded with far reaching vistas to the snow-capped sub-alpine peaks of San Jacinto and San Gorgonio to the west, while the Little San Bernadinos complete the panoramic view across the valley to the north. Te Living Desert’s Lawrence A. Cone, M.D., Bighorn Mountain exhibit is nestled onto the terminus of a rocky spur tumbling down from the Santa Rosas. It is an unsurpassed introduction to this endangered species amidst a setting befitting its iconic status. Te resident bighorn have cleared their enclosure of any naturally occurring vegetation over the years and visitors often ask ‘What do they eat?’
Peninsular bighorn sheep are tasked with the challenge of
sustaining themselves on the sparse vegetation that dots the stony ramparts adjoining some of the most arid lands found in the U.S. and along the length of the mountainous crest of the Baja California peninsula. Te northern extent of their distribution is the San Jacinto Mountains. Troughout their range they are considered a low elevation bighorn being typically found at elevations ranging from 300 to 4,000 feet and not venturing much above the upper limit of desert scrub.
Te sheep survive in a land that sees little rain and that
routinely experiences maximum daily temperatures that reach triple digits for months at a time. How can the inhospitable canyons and slopes in this land of thorn and stone support large herbivores like the bighorn sheep?
Deciphering the bighorn diet is an inexact science and the
best that can be hoped for is an estimation of which plants, and how much of each, are eaten. Desert bighorn diets have been studied throughout the southwestern U.S. from Anza
Borrego to Death Valley and the mountains of Arizona, New Mexico, western Texas, and southern Nevada. While there is some commonality of plant species amongst these widely spread desert ranges the composition and seasonality of each regional flora may be as varied as the bighorn’s use of it. Te diet of our local population of bighorn sheep was recorded over the course of a one year study by Joan Scott with assistance from Jim DeForge and the staff at the Bighorn Institute. Her research in 1981/1982 focused on the composition and nutritional value of the ewe diet in response to the rapidly declining population and rising lamb mortality of the local herd of bighorn sheep and also entailed smaller samplings of ram and lamb diets.
Several methods have been used in assessing the bighorn
diet, each with limitations. Direct observation of feeding habits proves challenging in being close enough to get accurate data without spooking the animals. Recording the feeding activities of captive herds may not represent the true habits of free roaming bighorn. Inferred foraging activities, checking plants which have been browsed in known bighorn habitat, become less clear if the bighorn share their range with other herbivores. Checking the rumen contents requires dead animals and expedient lab work, not the best conservation method for an endangered animal.
Scott utilized microhistological analysis of fecal samples as
a non-invasive approach to examining the bighorn diet. Tis method of diet determination is based on microscopic recognition of the generally unique and identifiable silica structures of digested plant leaf tissue. Te microhistological technique has been applied successfully to samples from extinct species such as the giant ground sloth and mammoth. Te drawback to this method is that results may over or under represent certain plants due to differences in digestibility, condition of plants at time of ingestion and/or sample preparation techniques.
Photo by Chris Pyle
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