THE SEA OTTER IN THE EASTERN PACIFIC OCEAN 305 



Because of the frequency with which it occurred, the edge of the 

 pool eventually became damaged and zoo officials removed the 

 rocks from the pool. 



The primary purpose of these observations was to ascertain 

 whether behavior differed in response to temperature or other 

 environmental seasonal conditions. All conditions, except those 

 associated with season, were similar in the two observation periods. 



On 29 August the weather was clear and calm. On 21 January 

 a high overcast persisted until 1300, after which the sky remained 

 clear until sunset. 



The summer maximum temperature was 26° F. (18.5° C.) above 

 the winter maximum and the winter minimum was 17° F. (9.5°C.) 

 below the summer minimum on the days of observation. This 

 temperature difference and the difference in hours of daylight 

 (4 hrs., 13 min. less in winter, table 63) apparently did not ma- 

 terially affect the otter's general pattern of daily activity. In spite 

 of the differences in these environmental conditions, the percent 

 of time that the otter spent in the four main activities recorded 

 are similar (table 62). 



The amount of time that the otter spent on land, however, 

 showed seasonal differences. On the summer day the otter was 

 in the pool both at sunrise and at sunset. On the winter day she 

 was in her den at both these times. Also, in the winter she spent 

 a greater percent of her time during the day on land, even though 

 her actual time on land was nearly identical (174 and 171 minutes, 

 table 62). 



Figure 116 shows the distribution of activity by minutes 

 throughout the summer day. (Because of its similarity, a chart for 

 the winter day is omitted. ) This shows that grooming periods were 

 generally distributed through the day, that periods of exercise 

 were concentrated in morning and late afternoon hours, and that 

 periods of rest reached greatest frequency at midday and in the 

 afternoon. There were five prolonged rest periods of relative inac- 

 tivity on the summer day: from 1126 to 1222, from 1340 to 1430, 

 from 1502 to 1542, from 1733 to 1831, and from 1907 to 1944. 



Table 62 demonstrates that the amount of time spent in muscular 



Table 6S. —Conditions during se 



',a otter observations at 



the Seattle Zoo 





29 August 1957 



21 January 1960 



Sunrise 



Sunset . 



Hours of sunlight- 



Air temperature (range) 



Water temperature (constant) 



0527 



1853 



13 hrs. 26 min. 



52° to 70*' F. 

 ... 62° F. 



0740 



1653 

 9 hrs. 13 min. 

 35" to 44° F. 

 38° F. 



