Earth's tallest animal is in deep trouble. Wild giraffe populations are plummeting due to poaching and habitat loss, with new survey data showing the mammals' numbers have fallen more than 40 percent over the last 30 years. And unlike the well-known plight of gorillas, elephants, rhinos and other disappearing African icons, the decline of these serene giants has gone largely unnoticed.

About 150,000 wild giraffes existed as recently as 1985, but there are now fewer than 97,000, according to the International Union for Conservation of Nature (IUCN), which has moved giraffes from "Least Concern" to "Vulnerable" on its Red List of Threatened Species. Their population pales in comparison to African elephants, for example, which number around 450,000 but whose decline has drawn closer study and wider publicity. That contrast isn't meant to diminish the real danger facing elephants, but it does highlight what Namibia-based Giraffe Conservation Foundation (GCF) director Julian Fennessey calls a "silent extinction" of giraffes.

"While there [has] been great concern about elephants and rhinos, giraffes have gone under the radar but, unfortunately, their numbers have been plummeting, and this is something that we were a little shocked about, that they have declined by so much in so little time," Fennessey recently told the BBC.

Despite their extreme height — adult males can stand nearly 20 feet (6 meters) tall — giraffes have been overlooked by many scientists and conservationists. This is likely due to a longstanding belief that giraffes are abundant, experts say, as well as a lack of definitive data proving otherwise.

"When I first became interested in giraffes in 2008 and started looking through the scientific literature, I was really surprised to see how little had been done," University of Minnesota Ph.D. student Megan Strauss told the New York Times in 2014. "It was amazing that something as well known as the giraffe could be so little studied."

Giraffes in the wild Giraffes eat up to 75 pounds of leaves daily, often traveling miles to find enough food. (Photo: EcoPrint/Shutterstock)

Of the nine subspecies of giraffes, five of those have had falling populations, one is steady while three have defied the odds and grown. "The species in southern Africa, those numbers are increasing by two to three times over the last three decades," Fennessey told the BBC. But the African Wildlife Foundation estimates fewer than 200 West African giraffes remain in Niger, while the population of Rothschild's giraffes in Uganda and Kenya is below 700 and falling, according to a report by the nonprofit Elephants Without Borders.

The IUCN noted in 2010 that Rothschild's giraffes may be near the threshold for a "critically endangered" listing, and also acknowledged emerging hints of trouble for the broader species: "[A] recent preliminary population estimate suggests a decline in the total population has taken place which, if substantiated, could mean that the species will warrant listing in a higher category of threat."

Giraffes still inhabit 21 countries in Africa, but swaths of their habitat are being repurposed for human use, especially agriculture. Even in places where their native grasslands remain intact, fragmentation caused by development elsewhere can restrict their range and hinder genetic diversity, while climate change can encourage lengthy droughts that may compound other pressures. And beyond their rapidly changing environment — which lead desperate giraffes to feed on farmers' crops, making them seem like pests to local communities — the animals are also increasingly threatened by poaching.

Giraffes in the Masai Mara National Reserve in Kenya, Africa Giraffes still inhabit 21 countries in Africa, but swaths of their habitat are being repurposed for human use, especially agriculture. (Photo: Travel Stock/Shutterstock)

Humans have a long history of hunting giraffes, seeking food as well as thick, durable skin to make clothing and other items. But a belief that giraffe brains and bone marrow can cure HIV has gained traction in Tanzania, reportedly pushing prices for a head or bones as high as $140 per piece. And since giraffes are relatively easy for humans to kill, often with a single gunshot, they've also become a popular source of food and extra income among Africa's growing hordes of elephant poachers.

When humans do stick out their necks for giraffes, however, there's evidence it can quickly improve the animals' fortunes. The West African giraffe, for example, was pushed to the brink of extinction in the 1990s by human population growth and a series of droughts. Down to just 50 individuals in 1996, the subspecies won legal protection from the government of Niger, helping it rebound to 250 individuals in 2010. Conservationists have also worked with villages in Niger to plant 5,300 acacia trees since 2012, reducing the need for giraffes to raid crops.

Editor's note: This story has been updated since it was originally published in December 2014.