Wildlife refers to all living organisms (terrestrial, aquatic and aerial) living in all possible natural habitats of their own, other than the cultivated plants and domesticated animals. Thus 'wildlife' does not exist only in jungles and are hunted down but wildlife includes even the migrating birds, turtles, coral reefs, microorganisms, insects, fishes, etc. Several hundred organisms are endangered or on the verge of extinction. The reasons are deforestation, pollution, killing, overexploitation etc. The most important among them is deforestation or destruction of their natural habitat because it will affect the species (flora and fauna) of the complete area and not only a few organisms. The natural habitat may be destroyed by man for his settlements, grazing grounds, agriculture, mining, industries, dam building, etc. As a consequence of this, the species must adapt to the changes, move elsewhere or may succumb to predation, starvation or disease, and eventually dies.
So, the correct answer is 'Destruction of habitat'.