Off toward distant horizons this summer afternoon, only small groups of a dozen or fewer migrating caribou could be seen grazing southward across the spongy landscape, green with a layer of grasses, mosses and lichen over the Arctic permafrost.
"I've never seen it like this before," Mr. Firth said of the sparse numbers.
More than 50 identifiable caribou herds migrate over huge wilderness tracts in a wide band circling the top of the world. They head north in the spring to ancient calving grounds, then back south through summer and fall to winter ranges closer to northern forests.
The Porcupine herd moves over a 100,000-square-mile range, calving in the Arctic National Wildlife Refuge, near Alaska's north coast, where proposals for oil drilling have long stirred opposition from environmentalists seeking to protect the caribou.
The global survey by researchers at the University of Alberta, published in June in the peer-reviewed journal Global Change Biology, has deepened concerns about the caribou's future.
Drawing on scores of other studies, government databases, wildlife management boards and other sources, the biologists found that 34 of 43 herds being monitored worldwide are in decline. The average falloff in numbers was 57 percent from earlier maximums, they said.
Siberia's Taimyr herd has declined from 1 million in 2000 to an estimated 750,000, as reported in the 2008 "Arctic Report Card" of the U.S. National Oceanic and Atmospheric Administration.