250 
Rand & Rand 
Table 3. Escalation of Displays 
Successive Displays by an Iguana Irrespective of the 
Intervening Act of Her Opponent 
First Display 
Second Display 
Mouth 
open 
Head 
swing 
Huff 
Head swing/ 
huff 
Lunge 
Lunge/ 
huff 
Bite 
Mouth open 
1 
1 
1 
Head swing 
2 
1 
4 
Huff 
1 
9 
2 
9 
3 
2 
Head swing/huff 
3 
2 
2 
1 
Lunge 
1 
2 
3 
Lunge/huff 
2 
Bite 
1 
1 
display, the more likely it is to be effective. 
Only in the ultimate display involving the 
bite does the one lizard touch the other. 
Why, then, does an iguana use any display 
other than the most effective one? We sug- 
gest that part of the explanation revolves 
around the energetic cost of giving the dis- 
play; and the energy expended in a display 
is a “statement” by the displaying lizard of 
how much energy she is willing to invest 
in defense of the hole. This inference is 
supported by the agreement found when one 
compares the ranking of displays by ener- 
getic cost and the ranking by the eventual 
outcome of the dispute. Iguanas that used a 
low intensity display lost the encounter more 
frequently than did those that used high 
energy displays. 
If the energy cost of displays is important, 
one might expect that the tactic of using a 
low energy display whenever it was likely to 
succeed would be part of the strategy and 
that occasionally an iguana might be ex- 
pected to use a low energy display even when 
fully capable of expending more energy. We 
find that this appears to be the case when 
we compare the sequences of displays given 
by the same individual in a single dispute 
shown in Table 3. The data indicate that, 
during a dispute, energy expended in dis- 
plays tends to escalate; if a low energy dis- 
play does not work, the lizard often next tries 
one that is more emphatic. 
In conclusion, we have tried to summarize 
here a very complex situation in which we 
have attempted to show that nesting female 
iguanas in dispute situations behave as if 
they were evaluating probabilities and 
energy costs and that such considerations 
“decide” their actions. 
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