How does an animal species qualify for the IUCN Red List?

Question

When does a "threatened species" of animal or plant become considered "endangered" by the World Conservation Union? Is there a specific number? Or a rate of decline? When exactly does the red flag get thrown?

Answer 1

Every Species need certain population to survive on a long term on earth. In IUCN that threshold population is considered based on several criteria,categorize the animal or plant as Critically Endangered, Endangered or Vulnerable. This is how it is done in general if you want to know what these criteria are then you better visit this link.

http://www.iucnredlist.org/info/categori...

The same info is available in IUCN Red Data Book.

Answer 2

The number would vary depending on the species, and the rate of decline varies, too, but is more constant for certain types and habitats.  There are biological "hot spots," and many endangered species come from these areas, as development and other human impacts tend to have a dramatic effect.  The red flag is typically thrown too late.  There are high profile species like the California Condor where all are removed from the wild and millions spent to manage the species, but the core problems in that situation and many others are not properly addressed.  

Still, this is a fantastic program. The World Conservation Union has been acting as a driving force in the Global Strategy for Plant Conservation (GSPC). Governments that met in Paris in July have pledged support for saving plants, the basis of all life on earth. This is encouraging, and will prevent a lot of "red flags" from being thrown in the future.