TRACKING WILDLIFE BY SATELLITE 



30 

 25 

 20 

 15 

 10 

 5 



NE Alaska 



NOAA-11 

 NOAA-10 



Maine 



2 4 6 8 10 12 14 16 18 2022 

 Hour (UT) 



Fig. 3. Satellite coverage at three representative sites in North 

 America. UT = Universal Time. 



satellite prediction computer program. Given a set of orbit 

 data as a starting point in their calculations, such programs 

 calculate times and characteristics of satellite overpasses. 

 The accuracy of pass predictions decreases as the time 

 between the known orbit data (available from NASA) and 

 the predicted orbits increases. However, predictions six 

 months into the future introduced an error of only 3 min 

 (Fancy et al. 1988). 



Other considerations for a duty cycle must be dictated 

 by study objectives. For example, it may be worth sacrific- 



ing length of operation in order to gather intensive data 

 during a particular season. Alternatively, it might be desir- 

 able to reduce the number of animal recaptures to replace 

 the collar, resulting in a duty cycle that sacrifices number 

 of locations but extends battery life. Cycling periods that 

 are integer multiples of 24 h will result in locations being 

 obtained at approximately the same time each day. For 

 some objectives, this may compromise the randomness or 

 independence of the sample (Swihart and Slade 1985a). 

 The minimum number of hours of transmission needed 

 to ensure a location estimate depends on latitude, charac- 

 teristics of the satellite overpasses (e.g., maximum satel- 

 lite elevation), and characteristics of the study animal 

 (e.g., its behavior and habitat). Our experiences suggest 

 that a location estimate from PTT's on terrestrial species 

 can be expected from about half the satellite overpasses 

 that have a maximum elevation over the study area of 15 

 or greater. 



Performance in Gathering 

 Wildlife Data 



The following sections present results from nearly 

 1,000 PTT-months (1 PTT month = 1 PTT operating 1 

 month) involving 10 mammalian species. First, we sum- 

 marize PTT survival rates. Second, we discuss efficiency 

 in obtaining locations and sensor information among 

 PTT's operating normally. Next, we explore the precision 

 and accuracy of locations obtained through the Argos 

 system, and then we present results of our calibration 

 experiments with activity indices and application of these 

 experiments to free-ranging caribou. 



Reliability 



PTT Survival Rates 



Generalizing PTT survival rates across species and pro- 

 jects was difficult because duty cycles differed, resulting 

 in differing life expectancies. Here, we differentiate be- 

 tween a failure to record locations, which we term location 

 failure, and a failure to receive any data at all, which we 

 term message failure. We do not differentiate among the 

 many possible causes of failure but believe that most 

 failures were due to premature battery depletion. For car- 

 ibou, we used duty cycles that theoretically provided a life 

 expectancy of one year. Reliability of caribou PTT's was 

 high. Of 45 PTT's deployed before or after March 1987, 

 only 5 failed: 3 experienced message failures almost im- 

 mediately, 1 failed within 3 months, and another failed 

 within 8.5 months. All other collars functioned for a full 

 year and were still operating when removed. As of late 



