In the twentieth century, conservation biology became one of the forms of expert knowledge contributing to governmental efforts to manage territories and populations. This article offers a situated account of the development of one of the key concepts deployed by biologists for such purposes in the mid-twentieth century: territoriality. It focuses on the work of Helmut K. Buechner, an American wildlife biologist who spent two years in Uganda on a Fulbright fellowship in the late 1950s and remained engaged with East African conservation into the 1970s. Building on observations of Uganda kob made by his wife, Jimmie Buechner, Buechner was able to demonstrate the existence of a complex territorial breeding system in a mammal for the first time. The existence of such a system, like the ability of the Buechners to observe it, was in part a product of the colonial land regime, which allowed dense antelope populations to develop within protected areas where they could be easily studied. The discovery of the kob’s territoriality encouraged speculation about the fundamental nature of the territorial instinct and contributed to the biologization of postcolonial conservation. In the 1960s and 1970s, biologists began to argue that conservation was more than a “numbers game”; it also required taking into account nonhuman traditions and social structures. The theory of biological territoriality thus became a conceptual tool for asserting nonhuman claims to land, often in competition with human claims. Colonial and postcolonial land-use regimes, Benson argues, can only be understood by studying such tools for the management of nonhuman populations alongside those applied to humans.