Photograph by Christian Ziegler

Voice of a forest, the red-eared monkey is the most abundant of Bioko Island’s 11 primate species. At least 12,000 years of isolation from mainland Africa has helped produce a one-of-a- kind ecosystem where life blooms from canopy to soil.

Photograph by Joel Sartore

Fireball Lily (Scadoxus cinnabarinus)

Photograph by Joel Sartore

Giant crab spider (Olios sp.)

Photograph by Joel Sartore

White-bellied kingfisher (Alcedo leucogaster)

Photograph by Joel Sartore

Centipede (order Scolopendromorpha)

Photograph by Tim Laman

The Olé River meanders and falls through the Gran Caldera—a volcanic crater formed millennia ago, now dense with forest.

Photograph by Christian Ziegler

Hunting by night, a house-cat-size linsang prowls into a camera trap for a portrait.

Photograph by Tim Laman

Twenty miles of ocean, rocky headlands, and boat-beating surf—like that pounding Point Dolores here on the southern coast—have helped keep Bioko wild. Most of the island’s estimated 150,000 people live in Equatorial Guinea’s capital city, Malabo, in the far north.

Photograph by Christian Ziegler

Island residents help land supplies on Moraka Beach in preparation for biodiversity surveys and the photographic blitz.

Photograph by Joel Sartore

Eyes trained on the treetops, Drexel University biologist Gail Hearn has been tracking Bioko’s primate populations for a dozen years. “It’s so lush here it’s overwhelming,” she says, “a real monkey paradise.” And unlike so many ecosystems worldwide, “humans are still in a position to save it.”

Photograph by Christian Ziegler

Found alone on the forest floor, this orphaned baby western tree hyrax became friendly with participants in the RAVE (Rapid Assessment Visual Expedition), but later died of an infection.

Photograph by Christian Ziegler

The toad Bufo tuberosus is found from Cameroon to the Democratic Republic of the Congo. Some members of its Bufonidae family have a gland that secretes a toxic goo potential predators find distasteful.

Photograph by Tim Laman

Gastropyxis smaragdina snakes through the trees on Bioko Island. There are nearly 2,500 species in its superfamily, the Colubroidea.

Photograph by Joel Sartore

Chained to a post in Malabo, where the bush-meat trade thrives, this orphaned drill may be sold as a pet, or become dinner for its captors. Bioko’s drill population shrank by a third from 1986 to 2006.

Photograph by Joel Sartore

Shoppers spend over $200 for a large male drill at the Malabo market, paying extra to have the fur singed off on-site. Chicken and other protein sources are readily available, and far cheaper than bush meat.

Photograph by Tim Laman

A thickly fruited fig tree provides nourishment for a Martin’s putty-nosed monkey. The rainy season lasts nearly all year in Bioko’s south; more than 400 inches of annual rainfall in some spots help a diverse garden grow.

Photograph by Tim Laman

Slow to leap, and an easy target for poachers, the Pennant’s red colobus ranks among the world’s most endangered primates. Preserving its island sanctuary demands good science—and law enforcement.

Photograph by Tim Laman

A Bioko black colobus monkey is at home in the island’s trees. “They are the most amazing jumpers,” says Drexel University primatologist Gail Hearn. “They are capable of amazing leaps. They launch themselves from trees at the edges of ravines and soar through space, landing in vegetation far below.” These monkeys are one of the fastest declining species on the island.

Photograph by Joel Sartore

As tiny leatherback turtles scramble from their nest on Moaba Beach, researchers Daniel Fitzgerald and Shaya Honarvar count 48 hatchlings.

Photograph by Joel Sartore

Instinct sends the young leatherback turtles seaward. Those that manage to elude hungry shorebirds and crabs face a gantlet of predators in the open ocean. Isolated Bioko Island is an ideal research site—and a haven—for the four endangered sea turtle species that nest on its shores.

Photograph by Joel Sartore

This fruit bat (lyssonycteris sp.) hangs with wings folded but will spend the evening hunting like other nocturnal predators on Bioko.

Photograph by Joel Sartore

Daylight brings out creatures like this gecko (Hemidactylus fasciatus).

Photograph by Christian Ziegler

Tussock moth caterpillar (family Lymantriidae).

Photograph by Joel Sartore

Flower (Rothmannia sp.)

Photograph by Tim Laman

A bush baby gazes from its sleeping tree with eyes that suit its nocturnal lifestyle. This one-pound primate subspecies is unique to Bioko. Hunters rarely take them, but biologists can’t ignore them. “They’ll sit on top of your tent and screech all night,” says Gail Hearn.

Photograph by Tim Laman

Because they reproduce quickly, blue duikers are relatively resistant to hunting pressure and are often found in the wild where other animals have been wiped out. These small antelopes are the wild animals most commonly offered for sale at the Malabo market. Scientists have counted more than 34,000 blue duiker carcasses there in the past ten years.

Photograph by Tim Laman

Bioko crowned monkeys “have great personalities,” says primatologist Gail Hearn, who founded the Bioko Biodiversity Protection Program a decade ago. “They’re punky with their Mohawks.” These primates seem to be taking advantage of their kin’s misfortune, gradually expanding their range into areas where other species have declined.