RELATED: SEE 10 OF THE RAREST ANIMALS ON EARTH
Published 18 Jan 2018, 17:35 GMT, Updated 18 Jan 2018, 18:49 GMT
Photograph by Joël Sartore
Harapan, a four-year-old male Sumatran rhinoceros at Florida's White Oak Conservation Center, appears to emerge from the shadows in this photograph. The total population of this critically endangered species is estimated at fewer than 275 individuals. Like other rhinos, this species has been heavily targeted by poachers who are after its horns.
Photograph by Joël SartoreSeemingly in awe, a six-week-old female western lowland gorilla has its picture taken at the Cincinnati Zoo.
Surveys since the 1980s suggest that commercial hunting and outbreaks of the Ebola virus are behind the gorilla species' plummeting numbers in its native Africa. (Watch a video of lowland gorillas.)
Photograph by Joël SartoreThe pygmy mouse is the only Australian mammal that lives in alpine environments.
But the small creature has been declining as its habitat is severely fragmented or destroyed by various construction projects and ski resorts. (See pictures of ski resorts that are trying to minimize their environmental impact.)
Photograph by Joël SartoreThe Philippine crocodile, pictured above, is a relatively small freshwater crocodile: Males usually don't grow more than about 10 feet (3 meters) long, and females are even smaller.
The reptile's habitat-lakes, ponds, marshes, and other bodies of water-has been widely converted into rice paddies. The animal has also suffered from hunting and destructive fishing methods such as the use of dynamite, according to IUCN. (Learn more about threats to freshwater.)
Photograph by Joël SartoreA Sumatran orangutan at the Gladys Porter Zoo in Brownsville, Texas, seems to pose for a portrait.
Native to the island of Sumatra, Indonesia, Sumatran orangutans are almost exclusively tree dwellers—a lifestyle that's led to their decline as Sumatra's forests increasingly fall to logging.
The great ape has dropped in number by 80 percent in the past 75 years, and scientists estimate there are only about 7,300 left in the wild.
Photograph by Joël SartoreThe northern bald ibis (pictured, an individual at the Houston Zoo) was thought extinct until it was rediscovered in the Syrian desert near Palmyra in 2002. Habitat disturbance and hunting are the main drivers behind the bird's decline in its Middle Eastern habitat. (See more bird pictures.)
According to a Turkish legend, the northern bald ibis was one of the first birds that Noah released from the ark, as a symbol of fertility.
Photograph by Joël SartorePhotographed at the National Aquarium in Baltimore, this black-eyed tree frog belongs to a species that scientists predict will decline by more than 80 percent over the next ten years.
Native to Mexico and parts of South America, the frog is under threat from habitat destruction and the chytrid fungus, an infectious disease that is decimating amphibians around the world. (Read about vanishing amphibians in National Geographic magazine.)
Photograph by F. Rovero, MuseA Lord Howe Island stick insect, photographed at the Melbourne Zoo, seems to peer into the camera.
The insect was thought to have become extinct around 1920 after the introduction of rats to Lord Howe Island (map), which is located between Australia and New Zealand.
However, in 2001, the species was rediscovered on Ball's Pyramid, a rocky outcrop located about 15 miles (22 kilometers) from Lord Howe Island.
Photograph by Joël SartoreSartore photographed this addax, or white antelope, at the Gladys Porter Zoo.
Scientists estimate that only 300 wild individuals of this critically endangered species remain; its population has plummeted due to hunting, drought, and even pressure from tourism. Once widespread throughout large swaths of Africa, it is now found only in Niger.
Photograph by Joël Sartore