28 



FISH AND WILDLIFE TECHNICAL REPORT 30 



cu 



c 

 .0 



*- 

 1_ 

 O 

 Q. 

 O 



Inactive 

 Walking 



Feeding 

 Running 



O N D J 

 1986 



A M J J 

 1987 



Fig. 24. Mean proportion of time spent in four activities by free- 

 ranging caribou in northern Alaska, October 1986-October 

 1987, as estimated by the short-term activity index. 



1i 



Inactive 

 Walking 



Feeding 

 Running 



June 



July 



Fig. 25. Mean proportion of time spent in four activities by six 

 free-ranging caribou in northern Alaska during June and July, 

 1987 as estimated by the short-term activity index. 



conditions, but other data suggest that these relations 

 break down somewhat under field conditions. The tem- 

 perature sensor cannot respond to rapid changes in ambi- 

 ent temperature because the canister and internal PTT 

 components have an insulating effect. In one experiment, 

 4 third-generation PTT's were moved from ambient tem- 

 peratures of roughly 4 C to 24 C. At the end of the 

 experiment (50 min), the temperature sensors read be- 

 tween 13.5 and 14.5 C (Fig. 26). These sensors seem to 

 require > 1 h to register such an extreme change in an 

 animal's microclimate. In addition to the time lag, other 

 factors that may cause the PTT temperature to differ from 

 ambient temperature include possible warming by the ani- 



14 



Ambient Air Temperature 



Transmitted PTT Temperatures 



10 20 30 40 50 



Minutes since Temperature Change 



Fig. 26. Delayed response of temperature sensors within four 

 third-generation PTT's to a sudden change in ambient tem- 

 perature from 5 to 25 C. 



mal's body and by the electronic circuitry itself. Pank et al. 

 (1985) were able to explain only 59% of the variance in 

 ambient temperature (measured in a shaded area 50-100 

 m away) and PTT temperature when collars were attached 

 to captive caribou. PTT temperatures were most often 

 warmer than ambient temperatures. The relation between 

 PTT temperature and ambient temperature will probably 

 vary among species, seasons, and PTT placement on the 

 animal's body (e.g., Johnsen et al. 1985). 



Saltwater Sensor 



Two prototype PTT's equipped with saltwater sensors 

 were deployed on polar bears in spring 1987, one each in 

 the Chukchi Sea and Beaufort Sea. An internal clock 

 counted the number of seconds of immersion within each 

 72-h duty cycle. An additional counter recorded the num- 

 ber of times the PTT was immersed in salt water > 5 s 

 during each 72-h cycle. 



According to the data, the Chukchi Sea bear spent much 

 more time in saltwater than the Beaufort Sea bear (Fig. 

 27). We recorded only 9 immersions for the Beaufort bear 

 but 1,522 for the Chukchi bear during the same period. 

 Reasons for the time differences in saltwater immersions 

 between the two bears are unclear. Independent evidence 

 suggests the Chukchi Sea bear may have had more access 

 to open water than the Beaufort Sea bear; however, mal- 

 functions or inconsistencies between the sensors cannot 

 be ruled out. 



