In the late spring, the 4000 elk of the Clarks Fork herd leave crowded winter grounds near Cody, Wyoming, following the greening grass into the highlands of the Absaroka Mountains, where they spend the summer growing fat on vegetation fed by snowmelt. It's a short trip (40-60 kilometers) by migratory standards, and by modern standards, uncommonly free of roads, fences, metropolitan areas, and other human-built barriers. But it crosses an important human boundary: the border into Yellowstone National Park.
The costs of migrating to the high green pastures have lately outstripped the benefits, according to a research report in the June issue of the Ecological Society of America's journal Ecology, published last week. Arthur Middleton and colleagues at the University of Wyoming, the Wyoming Game and Fish Department, and the U.S. Geological Survey reported that the migratory Clarks Fork herd has been returning to winter grounds with fewer and fewer calves over the last few decades. Herds that remain in the vicinity of Cody year-round have more surviving calves. Middleton et al. attribute the change in migration fortunes to climate change and a resurgence within the park of predators that hunt newborn elk calves.
In a Forum edited by Marco Festa-Bianchet, of the Universit de Sherbrooke, Qubec, five working groups of ecologists commented on the data, praising Middleton and colleagues' work, but, in some cases, challenging their interpretation. Middleton and colleagues addressed the commentary in a rebuttal.
Historically, migratory hoofed beasts like elk have outnumbered sedentary members of their species by as much as an order of magnitude. John Fryxell, a Forum contributor, wrote a classic paper on this effect in the American Naturalist in 1988. Mig
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Ecological Society of America