it to be easily detached. The tail is regenerated later, but the energy cost to the animal of replacing it is significant. Some frogs and toads inflate themselves to make themselves look large and fierce, and some spadefoot toads (Pelobates spp) scream and leap towards the attacker. Giant salamanders of the genus Andrias, as well as Ceratophrine and Pyxicephalus frogs possess sharp teeth and are capable of drawing blood with a defensive bite. The blackbelly salamander (Desmognathus quadramaculatus) can bite an attacking common garter snake (Thamnophis sirtalis) two or three times its size on the head and often manages to escape. Cognition In amphibians, there is evidence of habituation, associative learning through both classical and instrumental learning, and discrimination abilities. In one experiment, when offered live fruit flies (Drosophila virilis), salamanders chose the larger of 1 vs 2 and 2 vs 3. Frogs can distinguish between low numbers (1 vs 2, 2 vs 3, but not 3 vs 4) and large numbers (3 vs 6, 4 vs 8, but not 4 vs 6) of prey. This is irrespective of other characteristics, i.e. surface area, volume, weight and movement, although discrimination among large numbers may be based on surface area. Conservation Dramatic declines in amphibian populations, including population crashes and mass localized extinction, have been noted since the late 1980s from locations all over the world, and amphibian declines are thus perceived to be one of the most critical threats to global biodiversity. In 2004, the International Union for Conservation of Nature (IUCN) reported stating that currently birds, mammals, and amphibians extinction rates were at minimum 48 times greater than natural extinction rates—possibly 1,024 times higher. In 2006, there were believed to be 4,035 species of amphibians that depended on water at some stage during their life cycle. Of these, 1,356 (33.6%) were considered to be threatened and this figure is likely to be an underestimate because it excludes 1,427 species for which there was insufficient data to assess their status. A number of causes are believed to be involved, including habitat destruction and modification, over-exploitation, pollution, introduced species, global warming, endocrine-disrupting pollutants, destruction of the ozone layer (ultraviolet radiation has shown to be especially damaging to the skin, eyes, and eggs of amphibians), and diseases like chytridiomycosis. However, many of the causes of amphibian declines are still poorly understood, and are a topic of ongoing discussion. Food webs and predation