Life on the Rocks: A Portrait of the American Mountain Goat

Chapter Three: Behaving Appropriately

The mountain goat is one of the ruminants—the even-toed, hoofed mammals with complex stomachs where food is fermented by bacteria and protozoans to wring sparse nutrients from plants. Their digestive efficiency permits mountain goats to eat a variety of fibrous plants in winter when the availability of nutritious green forage is limited in temperate and subarctic regions. Although a specialist in many ways, the goat is a generalist in diet. Like most adaptations, this is a behavioral trait borne of necessity. During much of the year—November into May—snow suffocates their world. On canyon walls, where cliffs and crags face a southerly slanting sun, goats search the ledges and slopes for sparse patches of food. Winter after winter they repeatedly graze and browse plants at the windward edges of ledges, where snow depths are shallower. The specific composition of their catholic diet varies with snow depth, with stage of growth or curing of each plant, and with plant composition across the mountain goat’s continental range. Like wooly veg-o-matics, they paw through snow for grasses and sedges, nibble mosses and lichens from rocks, strip twigs from shrubs and trees, and sometimes dig the rhizomes of ground-hugging plants. On some Rocky Mountain ranges of CHAPTER THREE Behaving Appropriately DOI: 10.5876_9781607322924.c003 Kids remain with their mothers for a year, and sometimes longer. The strong bond between a nanny and her offspring ensures that during their first year of life, kids learn what plants to eat and where to find them, migratory routes to seasonal ranges, and other necessities of a life on the rocks. (Photo by author) 33 B E H A V I N G A P P R O P R I A T E L Y Colorado and elsewhere, wind sweeps the snow from shreds of tall ridges, and goats may outlast winter nibbling on dwarfed alpine plants at sky-scraping elevations. In Alaska and British Columbia’s coastal ranges—where snow piles higher than a house—goats descend far down the mountains (even to the seashore) and strip lichens from ancient trees in the dark depths of winter. Wherever they roam, mountain goats make do with what they can find. Winter is a period of energy conservation and waiting—waiting for the season of renewal, waiting for spring. Although finding tasty plants likely enhances a mountain goat’s energy balance and survival, filling one’s stomach is the first order of business when snow buries the land. I once watched a nanny goat in a Bitterroot canyon mangle a seven-foot-tall serviceberry bush—a preferred dietary shrub. All the lower branches, which would have been more tender and nutritious than the thumb-thick main stem, had been stripped by past browsing . She mouthed the main stem, twisted and tugged until finally she snapped it three feet above the ground. Then she munched each of the lateral twigs and finally ate part of the coarse main stem. Consuming small branches that have blown to the ground from ponderosa pine and Douglas fir trees are other instances where feeding efficiency wins out over searching and snow-plowing for more digestible morsels. Such behavior promotes energy conservation by reducing time spent foraging that burns the body’s precious fat stores. Goats live in a matriarchal society—a pecking order dominated by females that is common to species as diverse as bees, bonobo chimps, and elephants. Adult females (called nannies) command the highest social rank followed by subadults (two-year-olds and yearlings) and kids (those less than a year old). Among nannies, social rank increases with age. This dominance hierarchy is persistently reinforced with a complex repertoire of stares, postures, and threats—escalating degrees of aggression—that are well understood by all (see A Beast the Color of Winter for behavioral details). And this aggression is not spread evenly among all individuals. Adult nannies are by far the bossiest goats, as much as ten times more than adult males, who are called billies. Kids weigh just thirty-five to fifty pounds in winter (smaller than any other North American ungulate during its first winter) which renders them lowest on the pecking order and challenged to travel and forage effectively in deep snow. A kid remains with its mother until its first birthday (and sometimes until its second), nibbling food from the craters the nanny paws in the snow, gaining a...