Note: It is very difficult to figure out the exact moment at which the animal became extinct, and therefore, the concerned organizations have to wait for a significant period after the last sighting to declare it extinct. Simultaneously, thorough research is carried out to ascertain whether the species has really become extinct or it still exists in the wild.
The western black rhinoceros, for instance, was declared extinct in 2011, i.e., almost a decade after the last sighting, when all attempts to find it in the wild failed. If the species is not found in the wild, but is extinct in captivity, it is enlisted as Extinct in the Wild (EW).
depleted the wisent population to a great extent, with the numbers falling to less than 600 by 1917 and further down to less than 50 by 1921. The failure to curb poaching eventually resulted in the extinction of the Caucasian wisent, with the last reported individual being killed in 1927.
It was found in abundance at all elevations at one point of time, but the invasion of its natural habitat by the alien species resulted in its habitat being restricted to the dense montane forests of Hawaii by the 1920s. The population continued to decline, and eventually even the estimated 24 birds left in the wild by 1980s, succumbed to the circumstances.
are the best examples of the same. While rediscovery of a species is no doubt something to rejoice about, one also needs to understand that these species are not 'out of danger' as yet.
The exact cause of the extinction of dinosaurs may not have been ascertained as yet, but the cause of extinction of most--if not all--of the animals in the aforementioned list is no doubt traced to human activities, either directly or indirectly. These causes range from loss of habitat as a result of human activities to excessive hunting and poaching for food or their horns, skin, etc.
The grave picture doesn't just end there; the fact that the IUCN list of endangered animals continues to grow with time is also something which we have to be worried about. Last time the IUCN list was evaluated, i.e., in October 2012, 20219 species were threatened with extinction. Not even a year has passed, and the number has reached 20934 species; the list continues to grow. (Note: The number provided doesn't just include animals, but also includes plants, which are equally important for the planet's ecosystem).
The extinction of a particular species puts tremendous pressure on the fellow species as well as the ecosystem. It is but obvious that the tigers will be left with no option, but to encroach upon human settlements for food if the deer population is exhausted. Similarly, the number of herbivores will rise if the tiger population comes down, which, in turn, will lead to depletion of vegetation cover as a result of overfeeding by these herbivores.
The rate at which we are losing these animals is alarming, and if proper measures are not taken soon we may end up losing a large chunk of the animal kingdom - something which will indirectly affect us. In fact, the adverse effects have already started to show - and the man-animal conflict is a prominent evidence of the same. It's high time we understand that we are a part of the ecosystem, and any alterations in the ecosystem are invariably going to effect us.