Gorillas in Rwanda
American researcher Dian Fossey and her book "Gorillas' in the Mist" first brought international attention to the primates' plight. The mountain gorilla population dropped sharply in the last century because of poaching, illness and human encroachment, but their numbers are now rising - a hopeful sign for the critically endangered species.
These days, an estimated 900 mountain gorillas live in the steep-sloped forests of Rwanda and neighboring Congo and Uganda, the last of their species on earth.
In Rwanda, a country that has struggled with the ravages of genocide and civil war, conservation tourism is big business - seen as key to the welfare of the gorillas as well as Rwanda's economy.
In this photo, a male silverback from the Amahoro family sits in the dense forest on the slopes of Mount Bisoke volcano in Volcanoes National Park, northern Rwanda, September 4, 2015.
Rwanda's mountain gorillas
A mountain gorilla from the Amahoro family, which means "peace" in the Rwandan language, forages for food high in a tree in the dense forest on the slopes of Mount Bisoke, where the group has made their home.
In Rwanda, eighty individual permits to see the gorillas for one hour are available daily for a maximum price of $750 each (increased from $250 10 years ago), and 20 percent of permit revenue goes to schools, clinics and other local community projects, according to the park website.
More than 20,000 people visited Rwanda's gorillas in 2014, nearly three times as many as in 2003, according to government figures. Many came from the United States, Britain, Australia, Germany and Canada.
Rwanda's mountain gorillas
Tourist led by park rangers followed the gorillas after their morning nap in the dense forest of Volcanoes National Park, also known as "the land of a thousand hills."
After sipping coffee and milling around at the park headquarters tourists break into groups of eight, the limit to visit one of 10 separate gorilla families in the dense undergrowth.
It can take two to three hours of walking to reach the gorillas, through tangled vines, stinging nettles and other lush vegetation. Visitors are divided into groups based on the difficulty of their treks.
Rwanda's mountain gorillas
A baby mountain gorilla from the Amahoro family, which has 18 members, clings to the back of its mother as she forages for food on the slopes of Mount Bisoke volcano.
Females give birth after approximately nine months to newborns who generally only weigh four pounds. The baby gorillas stick to their mother's, riding on their backs from four months-old till they're two or three years-old.
Rwanda's mountain gorillas
The peak of Mount Bisoke volcano, where the Amahoro group has made its home, is seen above the flowers of potatoes grown by local farmers just outside the boundary of Volcanoes National Park.
Trackers monitor each of the 10 habituated gorilla families, making it a rare situation when tourists don't spot the gorillas.
Rwanda's mountain gorillas
Traditional dancers entertain tourists before they are briefed by park rangers for their trek to see the mountain gorillas.
Rwanda descended into bloody chaos during its 1994 genocide, and tourism only returned to Volcanoes National Park at the end of the decade.
Since then, Microsoft co-founder Bill Gates and Hollywood actors are among those who visited Rwanda's mountain gorillas, whose home is a two-hour drive from Kigali, the capital.
Rwanda's mountain gorillas
Tourists climb through dense vegetation and forest to see the mountain gorillas on Mount Bisoke volcano.
Visitors are told in advance the rules of the encounter: Don't point, speak softly, don't cough or sneeze in the animals' direction and stay a minimum of 23 feet (7 meters) away. If a gorilla approaches, crouch down, don't make eye contact and make a low sound similar to that of clearing the throat, which gorillas use to express friendliness.
Rwanda's mountain gorillas
A male silverback mountain gorilla, one of two in the Amahoro family, opens his mouth as a mother and baby sit next to him.
The silverback, the older male adult of the group with a swath of silver hair, is the leader. Though intimidating in size and stature, mountain gorillas are generally not aggressive unless they're disturbed.
Rwanda's mountain gorillas
A member of the Amahoro family takes a rest in the dense forest on the slopes of Mount Bisoke volcano, September 4, 2015.
Those same visitors who are seen as key to the survival of the species can also be a threat because gorillas are vulnerable to human diseases and so reduced in numbers that a veterinary team called Gorilla Doctors cares for sick and injured apes.
Rwanda's mountain gorillas
Members of the Amahoro family take a rest on the slopes of Mount Bisoke volcano, September 4, 2015.
When Gorilla Doctors veterinarians tend to injured gorillas it is a complex process that requires darting the primate with a tranquilizer and likely fending off other gorillas before treatment on the spot.
One of the members of the Amahoro family, Kajoriti, lost a hand to a poacher's snare.
Rwanda's mountain gorillas
Tourists, Sarah and John Scott from Worcester, England, take a step back as a male silverback mountain gorilla unexpectedly steps out from the bush to cross their path in Volcanoes National Park.
Sarah Scott, a nurse and wife of John Scott, said the close encounter was awe-inspiring. The gorillas seemed so human -- whether "grooming or passing wind" -- but also huge and powerful, she said, adding: "One swipe of the hand and that's it."
Rwanda's mountain gorillas
A mountain gorilla chews on leaves under tall bamboo on the slopes of Mount Bisoke volcano.
Rwanda's mountain gorillas
A baby mountain gorilla from the Amahoro family is held by its mother in Volcanoes National Park.
Female gorillas will only give birth once every three to four years; a low birth rate that affects the species' ability to recover from population decline.
Rwanda's mountain gorillas
Stephen Fernandez takes photos of a male silverback mountain gorilla in Volcanoes National Park.
Rwanda's mountain gorillas
According to the World Wildlife Fund, gorillas share 98.3% of their DNA with humans, making them our closest cousins after chimpanzees and bonobos.
For more information: Volcanoes National Park Rwanda