Canada's caribou population has reached "all-time low" levels, particularly in the eastern Arctic, where the animal was classified as endangered Monday along with the monarch butterfly, according to a committee of scientific experts.

"Caribou are, sadly, very sensitive to human disturbances, and we are disturbing caribou more and more," Justina Ray said in a report by the Committee on the Status of Endangered Wildlife in Canada (Cosewic).

"These stressors seem to be interacting in complicated ways with rapid warming in the North," she added.

"Many of the great northern caribou herds have now fallen to all-time lows, and there is cause for concern that they will not rebound in the same way they have before," according to the committee responsible for making recommendations to the government on the status of wildlife at risk.

Cosewic studied two populations of caribou: the tundra herd -- which it considers "threatened" -- and the rarer Torngat Mountain caribou in far northeastern Canada, which it assessed at an even higher risk -- "endangered." The latter is facing "imminent" destruction or extinction.

The causes of the caribou's decline include encroachment of its habitat by forestry and mining, and global warming, which is more pronounced in the Arctic.

The World Wildlife Fund (WWF) in October expressed alarm over the decline of Canadian caribou herds over the past three decades.

Cosewic also classified the monarch butterfly, another migratory species, as endangered. The committee said that the "remarkably tiny wintering grounds where monarchs congregate continue to be chipped away by habitat loss."

The insects travel 4,000 kilometers from Canada to Mexico each fall to escape the snow. The report calls for conservation of its habitat in Canada, along its migratory path through the United States and critical overwintering areas in Mexico.

"Otherwise, monarch migration may disappear, and Canada may lose this iconic species," it concluded.

In June, 200 American, Mexican and Canadian academics, scientists and artists wrote to the leaders of the three countries calling for banning mining and illegal logging in the Mexican reserve where monarchs spend the winter.

They also demanded a ban on the use of pesticides on plots where milkweed grows to preserve the only plant Monarch caterpillars eat.

The committee pointed to a particularly destructive herbicide used on genetically modified corn and soybean crops.