TRACKING WILDLIFE BY SATELLITE 



most 10-day intervals. The 2B versions failed at higher 

 rates early in their deployments, although 3B versions 

 failed at higher rates as deployments neared the expected 

 battery life (Fig. 4). The recently deployed generation 3C 

 PTT's had a message failure rate of 8.3% (3 PTT's) during 

 the first 140 days following deployment, suggesting im- 

 provement over the 3B version. 



Duty Cycles 



Fancy et al. ( 1 988) reported a few shifts or errors in duty 

 cycles of second-generation PTT's. Among the 56 PTT's 

 placed on caribou in 1987-88, we noted no similar shifts 

 or errors. All PTT's programmed for diverse duty cy- 

 cles on 4 muskoxen, 2 elk, 2 mule deer, 2 moose, 1 Dall 

 sheep, 1 1 brown bears, and 1 gray wolf operated without 

 detectable errors or shifts. 



To lengthen expected transmitter survival time from 

 414 to 648 days (Table 5), we altered duty cycles of PTT's 

 deployed on polar bears in 1988. We also documented the 

 reduction in location frequency resulting from the reduc- 

 tion in transmission hours per 72-h cycling period. Mean 

 (standard error; SE) locations per PTT within 72-h periods 

 were 4.38 (0.4 1 ) for 1 2/60 duty cycles, 2.74 (0. 1 1 ) for 8/64 

 duty cycles, and 2.27 (0.18) for 7/65 duty cycles. 



We considered a duty cycle successful for polar bears if 

 it yielded an average of at least one location per 72-h 

 period. Compared with 88% (SE 3%) for 8/64 PTT's and 

 82% (SE 3%) for 7/65 PTT's, PTT's with the 12/60 duty 

 cycle were successful during 91% (SE 7%) of cycling 

 periods. Reducing transmission hours per cycling period 

 by 33 and 42% produced 3 and 10% reductions in the 

 proportions of success. The degree to which altering duty 

 cycles succeeded in extending PTT longevity is not yet 

 known. 



Activity Sensor Malfunctions 



In late 1987, because of unusually low activity indices, 

 we began to suspect that some activity sensors in PTT's 

 deployed on caribou had malfunctioned. On inspection 

 following sensor removal (for refurbishing), 4 of 12 mer- 

 cury switches inspected were found to have cracks that 



resulted in biased data (S. Tomkiewicz, Telonics, Inc., 

 personal communication). PTT's deployed on caribou at 

 other times were not tested for mercury switch malfunc- 

 tions, although, based on the very low activity counts 

 obtained during visual observation (D. Vales, personal 

 communication), one of two PTT's on elk seemed to have 

 had a similar problem. The activity sensor on one of two 

 PTT's deployed on muskoxen in Greenland also malfunc- 

 tioned after two months of operation. 



Efficiency 



The quantity and quality of data received from individu- 

 al PTT's varied among projects. We examined hypotheses 

 that efficiency of data collection was influenced by lati- 

 tude, season, presence of topographic relief in the study 

 area, longevity of the deployment, and species. We de- 

 fined two monthly performance indices that provided 

 standardized measures of efficiency across projects, spe- 

 cies, duty cycles, and so forth. The message index for each 

 PTT was defined as the number of times at least one 

 message was received from that PTT each month, divided 

 by the total number of transmission hours during that 

 month; the location index for each PTT was the total 

 number of unique location estimates each month divided 

 by the total number of transmission hours during that 

 month. The latter index was a rough estimate of proba- 

 bility of obtaining a location during each hour of transmis- 

 sion time. Both indices adjusted for differences in duty 

 cycles among PTT's. 



Mean data collection efficiencies for 9 species in 12 

 study areas are summarized in Table 6. Walrus data are not 

 included because transmitters could only operate when the 

 animals were surfaced, thus there were no set expected 

 hours of transmission. Mean message indices varied from 

 a low of 0.37 for elk in Yellowstone National Park to a high 

 of 1.16 for muskoxen in Greenland (indices > 1.0 were 

 possible where satellite overpasses occurred more than 

 once per hour). Monthly location performance indices 

 varied from a low of 0.08 for Kodiak brown bears to a high 



Table 5. Platform transmitter terminals (PTT's) deployed on polar bears fUrsus maritimus) in the Beaufort, Chukchi, 

 and Bering seas during 1985-88. Sample sizes ofSC PTT's with different duty cycles appear in parentheses. Dates: 

 Sp = spring, Fa =fall. 



PTT generation 



