He drew from his first hand observations of Siberia and Northeast Asia, where he saw that animal populations were limited not by food sources, which were abundant, but rather by harsh weather. For example, predatory birds may compete by stealing food from one another while migratory birds cooperate in order to survive harsh winters by traveling long distances. He did not deny the competitive form of struggle, but argued that the cooperative counterpart has been under-emphasized: "There is an immense amount of warfare and extermination going on amidst various species; there is, at the same time, as much, or perhaps even more, of mutual support, mutual aid, and mutual defense...Sociability is as much a law of nature as mutual struggle."[5]