An Index of the Range of Activity

Abstract

The value of obtaining the range of activity by a statistical technique is emphasized. This technique permits statistical comparison of the normal range of movement of individual animals, different sexes, and different species. In addition, this technique permits comparison of the normal range of movement of animal populations of different study areas, within the same study area from year to year, and more importantly from one study to another. Examples of the use of this technique show range of animal activity is associated with population size and sex. Analysis of any animal population by the use of mark and release census techniques requires an examination of the amount of movement exhibited by the animals in that population. Extensive movement could result in animal contact with more capture devices or observation posts and consequently higher frequencies of capture or observation. Stickel (1960) indicates that variation in the size of the home range reduces the reliability of census. The concept of home range has been widely discussed in the literature and is most easily defined as the area over which an animal travels in its normal daily activities (Burt, 1943). Numerous methods for calculating the size of home range of individual animals have been presented. Most of these methods establish the home range as an area inside discrete boundaries beyond which the animal is assumed not to roam (Stickel, 1946; Mohr, 1947). Hayne (1949) presents the concept that some parts of the home range are more intensively used than others. Thus, the probability of capturing an animal in the more intensively used area is higher than the probability of capturing the animal in a little used portion of its home, range. Hayne (1949) gives a method for calculating the geometric center of activity of an individual animal, and suggests that the probability of capture of this animal decreases as the distance from the center of activity increases. The concept of zones of probability of occurrence about the center of activity is further discussed by Harrison (1958). Both Hayne and Harrison indicate that the probability of capture within a zone around the center of activity is an index of the intensity of the activity within that zone. Both authors discuss zones of probability or intensity of activity as concentric probability zones around the center of activity. Harrison (1958) presents a method for calculating the diameter of the concentric probability zone that contains 68.26 per cent of the captures and in theory 68.26 per cent 1 A portion of a doctoral thesis submitted to Rutgers, The State University, New Brunswick, New Jersey. 2 Current address: Department of Biology, Keuka College, Keuka Park, New York.