PRIMATES,15(2-3) : 271-278, September 1974 271 Demography of Macaca sylvanus of Gibraltar FRANCES D. BURTON and LAWRENCEA. SAWCHUK University of Toronto ABSTRACT. The demographic structure of Macaea sylvanus (Gibraltar) is analyzed over a 21 year period in light of human interference on this population. Social behaviour is examined in terms of its influence on the parameters investigated. The findings lead to speculations concerning the nature of homeostatic processes operating in a non-wild group. INTRODUCTION Populations are dynamic entities. Longitudinal studies asymptotically permit ap- proximation of a population's spatial-temporal condition. The inter-relationships between behavioural, genetic, ecological, and demographic determinants of popu- lation structure become apparent over time. There are few monkey populations in which such a study is possible, and none of these are 'wild' which is understood to mean that condition in which the sympatric human population exerts no more control than any other sympatric animal species, although it may prey on, or alter the ecology. This paper describes basic aspects of the demographic structure of Maeaca sylvanus of Gibraltar. The Gibraltar macaques have been previously described elsewhere (MACROBERTS & MAcROBERTS, 1966, 1971 ; MACROBERTS, 1970; BtmTON, 1972). Two free-ranging groups at Queen's Gate and Middle Hill constitute the population. The British Army has full responsibility for the animals, and provides approximately one third of their nutritional needs as well as water. Noxious elements are removed, as was the case in 1951 when a green locust tree, thought to be causing enteritis, was ordered to be cut down. Total population size is legislated, with surplus animals culled by the Keeper upon ultimate approval of the Governor, and sent to zoos. Composition of the popu- lation is thus left to the Keeper, who bases his judgement on social behaviour and breeding patterns. Health concerns are brought to the attention of an army doctor, and surgery is performed at the Naval Hospital. Rarely, animals that are badly injured or which represent a danger to the human or monkey population are destroyed. The current Keeper, Sergeant ALFRED HOLMES,has had this duty for over a decade, so that policy and procedure have been standardized for the past 15 years. The data used for this initial study were extracted from that portion of Army records which have consistency in terms of their collection and cover a period of political and social stability for Gibraltar. All data were organized into geneologically oriented units of information, that is the maternal sibship. Each individual within the sibship is characterized by sex, date of birth, place of birth, date of entry, residence, date of loss, cause of loss, and putative ancestry. The data described formed the basis