Of all the endangered species on the planet, the café marron, Spix’s macaw, Kihansi spray toad, American burying beetle, Sumatran rhinoceros, three-striped box turtle, and vaquita could be considered among those in the gravest condition. Sociobiologist E. O. Wilson predicts that if we don’t slow our consumption of natural resources, we’ll extinguish half the species of plants and animals by the end of the 21st century.

• The café marron, a member of the coffee family native to Rodrigues Island in Mauritius, had dwindled down to one survivor in the 1980s. That survivor, as well as its propagated cuttings, are male, making it impossible for the species to reproduce.

• Across the ocean in Brazil, researchers question the fate of another lone survivor. A male Spix’s macaw was last seen in its native woodland in October 2000. Virtually all of the 60 or so of its captive kin are privately owned, vestiges of what was once a thriving trade of their species.

• In Tanzania the tiny Kihansi spray toad hangs on in one of the most restricted ranges on the planet. A hydropower project dried up 95 percent of the toad’s habitat, making captive breeding in the U.S. its only chance for survival.

• Fragmented habitat and competition for carrion from foxes, raccoons, and skunks are severely reducing the populations of the American burying beetle, which plays a role in recycling decaying animals back into the ecosystem.

• In parts of Asia the demands of traditional medicine adversely affect populations of the Sumatran rhinoceros and the three-striped box turtle. The first is falling victim to poachers who sell its prized horns. The Chinese value the turtle’s flesh not only for its taste but also because of its purported cancer-curing properties.

• And little hope remains for the vaquita, a rare porpoise that lives in the northern end of the Gulf of California. Many have been snared by gill and trawl nets with only a few hundred surviving. Researchers have had no success at breeding or keeping them in captivity.