In the last few months the Western black rhino and the South Florida Rainbow Snake have gone extinct, as far as official recordkeepers are concerned. Less than 3,200 tigers remain as human development, pollution and climate change impinge on ever narrowing habitats.

Tracking these events is not easy. The worldwide arbiter—The International Union for Conservation of Nature (IUCN) —maintains a Red List of endangered species that has become the accepted standard. In the United States, the Endangered Species Act (ESA) establishes protections for animals on the brink. Or does it?

A recent study by scientists at the University of Adelaide and the Center for Biological Diversity (CBD) looked at which American animals made the ESA list, and which didn't. About 40 percent of the bird species listed by the IUCN didn't make the ESA list, and over 80 percent of other groups like fish, amphibians and insects. In total, 531 species that live in the United States and are listed by the IUCN didn't make the ESA cut.

See some of them here.

Being on the IUCN list isn't worth much, since it's simply informational. The ESA list, on the other hand, affords species government backed protection from things like development and hunting. The U.S. Fish and Wildlife Service, that maintains the ESA list, is often steeped in politics, which make listing species very difficult. There are hundreds of species under review by the agency, and those reviews are often delayed many years.