PERRIN and HUNTER: ESCAPE BEHAVIOR OF PORPOISE 



ZO S5 



30 35 



Vv^ 



.^V*^^ 



l-Jm *iOt ; Wm WIDE 



/ 



1 DEEP, WIDTH VARIED 



FAILED TO ESCAPE O 



55m WIDE; 

 DEPTH VARIED 



Sim WIDE; 

 DEPTH VARIED 



TRIAL NUMBER 



Figure 4. — Results of experiments with trained porpoise 

 Nohea. I. May 30, II. May 31, III. June 1, IV. June 21, 

 V. June 28, VI. June 29, 1970. 



blocks of six trials each (Figure 4-III). The 

 width of the escape route was 3.1 m in the sec- 

 ond, 1.5 m in the fourth, and 0.76 m in the sixth 

 block of experimental trials, with interspersed 

 blocks of trials at 5.5 m. A significant decrease 

 in performance occurred only when the escape 

 opening was narrowed to 0.76 m. In one trial 

 at 0.76 m the animal refused to leave the crowd- 

 ing chamber and had to be extricated from the 

 webbing. In others, the porpoise exhaled air 

 and sank passively to the bottom of the pool and 

 did not move even when the chamber was com- 

 pletely closed. Exhalation of air and sinking to 

 the bottom was a pattern that appeared in other 

 porpoise in other experiments and was accom- 

 panied by failure to escape. 



Our tentative conclusion was that the width 

 of the opening w^as not a significant variable in 

 the block experiments if it exceeded about 1.5 m. 



DEPTH OF OPENING 



We determined the effect of the depth of the 

 escape route by varying depth of the hole from 

 1.8 m to 0.15 m while maintaining the standard 

 hole width of 5.5 m. We will describe the results 

 for each porpoise separately since the experi- 

 ments w^ere diflFerent for each animal. 



Waimea failed in the first eight trials to escape 

 through an opening 0.92 m deep (Figure 2-1). 

 Performance improved thereafter to a plateau 

 that was maintained throughout a subsequent 

 identical experiment the next day, throughout a 

 series of alternating trials with 0.92-m- and 

 0.61-m-deep openings on the third day of the ex- 

 periments, and in a fourth experiment (Waimea 

 IV) 2 days later with a 0.92-m-deep opening. 



Nani showed no difference in response after 

 the first two trials with openings 1.8 m and 1.1m 

 deep (Figure 3-1). High performance contin- 

 ued through a series of trials with a 1.1-m-deep 

 opening, but dropped in blocks of trials of 

 0.61-m- and 0.30-m-deep openings (II). In sub- 

 sequent experiments Nani failed to escape twice 

 when openings 0.15 m and 0.30 m deep were used 

 and performed erratically in blocks of trials with 

 openings 0.61 m and 0.30 m deep (III). After 

 seven trials with the 0.30-m opening, no failures 

 was experienced in seven trials with a 0.15-m 

 opening, but the animal escaped consistently 

 earlier (larger remaining area) when the 1.1-m- 

 deep opening was used. 



Nohea escaped earlier when the hole was 1.1m 

 than when it was 0.61 m deep in 14 of the first 16 

 trials of an alternating series (Figure 4-1), In 

 a subsequent series of blocks of trials at decreas- 

 ing depths (II), a pronounced drop in perform- 

 ance occurred at depths of 1 ft and 5 ft. The 

 following day's performance remained at a high 

 level except when a corkline was strung across 

 the opening (IV). 



Our tentative interpretation of the above re- 

 sults was that a critical depth of opening lay near 

 1 m: 11 failures to escape occurred at 0.92 m 

 or shallower; none occurred with openings 1.1 m 

 deep or deeper; and performance was even more 

 adversely aflfected by further decreasing the 

 depth of the opening. We also concluded that 

 the results of the first few trials for each ani- 



53 



