Estimating temporal independence of radio-telemetry data on animal activity

Radio-telemetry is an excellent tool for gathering data on the biology of a nimals and their interactions with the environment they inhabit. Many metho ds have been developed for analyses of spatial information, on home range s ize and utilization density. Activity patterns are often described using ra dio-tracking data, but no generally accepted method is currently available specifically for determining the temporal independence of this type of data for statistical inference. Activity rhythms have generally been analysed b y ecologists with the assumption that data are temporally independent, or b y subjectively fixing an independence interval, based on attributes of thei r ranging behaviour. Although some good approximations of activity patterns can be obtained in these ways, we underline the need for a functionally co rrect method of estimating independence interval. Here we use semi-variogra ms to estimate the minimum interval required for the readings to be sequent ially independent. This geostatistical tool is applied to the analysis of d ata on activity of Chilean foxes (Pseudalopex culpaeus) and Chacoan peccari es (Catagonus wagneri). Data were collected in the field by radio-tracking over 24-hr periods, with readings on activity state taken every 15 min. The spatial dimension in which the theory of geostatistics lies has been trans ferred into the time dimension, so that the correlation interval is express ed in time units (min). Time of independence as estimated by the variogram was 110 min for foxes, while data on peccaries indicated that they have lon g periods of activity, more suitable for time-series analysis. (C) 1999 Aca demic Press.