The world's giraffe population is in sharp decline and could be facing a "silent extinction," according to wildlife conservationists.

The International Union for Conservation of Nature (IUCN) now lists giraffe's as "vulnerable" and has called for immediate action to reverse the decline of the population. That's two steps up the danger ladder from its previous designation of being a species of least concern.

Maasai Giraffe in a spectacular dawn Masai Mara National Reserve Kenya. Images of Africa Photobank / Alamy

Nearly 40 percent of the world's giraffe population has declined in the last three decades, IUCN said Thursday, fueled by habitat loss and illegal hunting. In 1985, there were between 151,000 and 163,000 giraffes, but in 2015 the number was down to 97,562, according to the IUCN.

At a biodiversity meeting Wednesday in Mexico, the organization increased the threat level for 35 species and lowered the threat level for seven species on its "Red List" of threatened species, considered by scientists the official list of what animals and plants are in danger of disappearing.

The giraffe is the only mammal whose status changed on the list this year.

While everyone worries about elephants, Earth has four times as many pachyderms as giraffes, said Julian Fennessy and Noelle Kumpel, co-chairs of the specialty group of biologists that put the giraffe on the IUCN Red List. They both called what's happening to giraffes a "silent extinction."

"As one of the world's most iconic animals, it is timely that we stick our neck out for the giraffe before it's too late," said Julian Fennessey, co-director of the Giraffe Conservation Foundation.

Despite worldwide affection for giraffes, relatively little research has been conducted into conservation of the species, the group said. Giraffes are native to the African savanna and are most commonly found in southern and eastern Africa. An adult giraffe can grow up to 19 feet and weigh more than 2,000 pounds, according to National Geographic.