Usually island ecosystems differ in poverty in comparison with continental ones. Few species can get on islands and survive in conditions of isolation. Island ecosystems differ in vulnerability, and strongly suffer from introduction of new species. Newly appeared species change a course of evolution of other inhabitants of ecosystem because actually they are the new factor of environment for native ones. But the introduced species change not less, than others, having got in new conditions. On New Azora Island the majority of mammalian species is descendants of species introduced by people. The special species of insectivores, the Azorean tree hedgehog – belongs to them. It is tree-climbing species of animals, the descendant of European hedgehog (Erinaceus europaeus) introduced in historical epoch. Earlier unite species had given two branches of descendants. The massive line of ground animals is presented by large azogalerix, and small descendants of European hedgehog turned to tree-climbing species. Change of way of life had resulted in strongly expressed difference of new species from ancestor in constitution and behaviour. Azorean tree hedgehog is not able to turn in ball, and the hypodermic muscles characteristic for ancestor became very weak at it. The body of this animal is still covered with the pointed spikes serving for self-defense. In case of danger the animal nestles against bark of tree and exposes towards to the enemy spikes which can rise and fall with the help of special muscles in the basis of each spike. In connection with tree-climbing habit of life at this animal there are relatively larger paws, than at ground hedgehog. Azorean tree hedgehog dexterously and quickly swarms up trees, and confidently keeps even on vertical surface of tree trunk. Fingers at Azorean tree hedgehog are more mobile; with their help animal can cling even to thin twigs. Besides this mammal has one more adaptation permitting to keep on trees better. On the back side of paws at this hedgehog especially strong and thick, slightly bent spikes grow in line. With their help the hedgehog can cling to bark, swarming up tree trunk and branches. Head at this animal is extended and flattened. The muzzle is extended in mobile proboscis with which help animal searches for forage. Ears at Azorean tree hedgehog are wide and mobile – it is necessary not only for search of prey, but also for more effective heat exchange in conditions of hot climate. At animal there is keen hearing due to which this hedgehog can hear noise of insect creeping on bark in night darkness. At this animal there is good night sight, but Azorean tree hedgehog distinguishes colors badly. The brain at this animal is small, and behaviour differs in primitiveness. Azorean tree hedgehog occupies an ecological niche of small prosimians in ecosystem of this island. This is a solitary animal eating mainly small animals – insects, tree-climbing land crabs and nestlings of various birds. Due to ability to climb on trees this animal can attack colonies of fog swifts settling in cavities of trunks of large trees. Also Azorean tree hedgehog eats mushrooms and juicy soft fruits. Among mushrooms the animal chooses the most worm-eaten ones, and eats them along with larvae of insects settling in them. The poison accumulating in some mushrooms does not harm to it – at Azorean tree hedgehog there is strong immunity to poisons, inherited from ancestor. Each individual occupies the certain territory which is marked by odorous secretions. Out of breeding season there are no constant shelters in territory of this little mammal. These animals meet only in period of pairing, and in another time protect the territory from relatives. The posterity at these hedgehogs is born two – three times per one year. In litter it may be up to 5 – 6 small, blind and helpless cubs. Before their birth the female searches for shelter in which it will raise cubs. Usually for this purpose it occupies hollows or old bird nests. If necessary the female can expel medium-sized birds from liked nests: it eats their laying or nestlings, and occupies the empty nest. Young animals abandon nest at the age of about two months. At this time they already see well and able to climb on branches. The litter keeps near to the female till two next weeks, training in ways of getting of food. One-year-old animals already can bring posterity. Life expectancy of this mammal does not exceed 6 years.