The loss of species from some areas of the world is particularly great. These areas are called biodiversity hotspots. A biodiversity hotspot is defined as an area with a high level of biodiversity that is under serious threat from human actions. Such hotspots are both the biologically richest and the most endangered terrestrial regions on the planet. To qualify as a biodiversity hotspot, an area must have a large percentage of endemic species (species native to that region and found nowhere else on Earth) and have already experienced loss of more than half of its primary producers. Biodiversity hotspots occur all over the world, but the most are found in forests. Hawaii is an example of a biodiversity hotspot. It is often called the “endangered species capital of the world.” It has more endemic species of plants and animals that are in danger of extinction than any other place on the planet. More than one-third of all the threatened and endangered birds in the United States are found only in Hawaii. There are 71 known taxa of birds endemic to the Hawaiian Islands, of which 23 are now extinct. Thirty more (including the Laysan duck pictured below) are threatened or endangered. There are approximately 50 % of the world's plant species and 42 % of all terrestrial vertebrate species that are endemic to the 34 biodiversity hotspots meaning about 2.7% of both plants and vertebrate species are present in a hotspot.