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IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008 49HISTORICAL PERSPECTIVE

The Marine Iguana (Amblyrhynchus cristatus) is a species
endemic to the Galapagos Islands. It lives in large aggrega-

tions along the rocky shorelines throughout the archipelago. It
is the only iguanid specialized for feeding on marine algae,
which they crop at low tide from the exposed rocks or even by
diving down to the bottom of the sea.

The animals are extremely gregarious and sometimes hun-
dreds of iguanas bask on the lava rocks in bodily contact with
each other. Besides this mutual attraction, however, no specific
forms of social interaction like grooming, mutual feeding ritu-
als, etc. are to be observed. This is in striking contrast to the
social behaviour of birds and mammals that use such patterns
for bond formation. These bond-forming behaviour patterns are
mainly derivates of maternal behaviour, which seem to be
preadapted for this purpose. Reptiles lack maternal behaviour
and this may in part explain their inability to form a closer bond
between adults.

During the breeding season the male Marine Iguanas
become territorial. They defend a small area of lava rock against
other males, whilst females are allowed to stay. If a male rival
approaches the territory, its owner displays. He opens his mouth,
nods with the head, and walks stiff-leggedly up and down in
front of the rival, showing his lateral aspect. The dorsal crest is
erected and the gular regions extended. If the rival answers by
the same display, fighting is initiated. The opponents rush at
each other. However, in spite of the biting intentions shown dur-
ing the display, they never bite each other, but instead lower their
head and butt. The hornlike scales on the roof of the head inter-
lock and the animals try to push the other away. This can con-

H I S T O R I C A L  P E R S P E C T I V E S

The Fighting Behaviour 
of Marine Iguanas1

I. Eibl-Eibesfeldt

Max-Planck-Institut, Seewiesen

1 Adapted from the original publication in the Philosophical Transactions of
the Royal Society of London. Series B, Biological Sciences, Vol. 251, No. 772, 
A Discussion on Ritualization of Behaviour in Animals and Man (29
December 1966), pp. 475–476.

The threat display of a Marine Iguana (Amblyrhynchus cristatus).

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50 IGUANA  •  VOLUME 15, NUMBER 1  •  MARCH 2008

tinue for a while, with pauses in between, during which the
opponents display frontally. The struggle ends when one of the
rivals is pushed from the rock or when he gives up by assuming
a submissive posture (lying flat on his belly). The winner then
stops fighting and waits in threat display for the rival to leave.
The fight is a highly ritualized tournament in the course of
which the stronger wins, without hurting the loser.

Only if one introduces a male artificially into the territory
of another male, can damaging fights be observed. Then the ter-
ritory owner rushes at the introduced individual, which does not
show the introductory ceremonies that normally release ritual-
ized fighting. The introduced individual is bitten as a conse-
quence.

Females fight in some places of the archipelago for the rare
egg-laying sites. In contrast to the males, their fighting is far less
ritualized. It begins with threat display and head-pushing, but
soon they bite and shake each other viciously. They have less
developed hornlike scales than the males.

Ritualized fighting is fairly widespread in animals that are
capable of inflicting serious damage to conspecifics. Poisonous
snakes never bite each other, but the rivals wrestle according to
the fixed rules. Cichlid fishes have developed various forms of
mouthfighting, and thus avoid mutual damage. In a number of

species (e.g., in wolves), fighting starts as a damaging fight, but
ends by a submissive posture of the loser, which inhibits further
aggression (Lorenz 1963). The existence of ritualized combats
shows clearly that the killing of a conspecific is generally avoided
in vertebrates. Only animals without weapons or animals that
can easily retreat after the exchange of bites have no such social
inhibitions. This is, for example, true for the hamster (Cricetus
cricetus), where the loser has no difficulty in running away. The
winner never follows far. In captivity, species of this type often
kill each other. From the fact that ritualized fighting occurs, we
can learn furthermore that strong selection favors aggression.
Otherwise aggression would have been counterselected in species
that can do damage to conspecifics. However, they developed
the most complicated fighting techniques instead, in order to
permit fighting, as a mechanism for spacing-out (Eibl-Eibesfeldt
1951, 1961).

References
Eibl-Eibesfeldt, I. 1955. Der Kommentkampf der Meerechse (Amblyrhynchus

cristatus). Zeitschrift der Tierpsychologie 12: 49–62.

Eibl-Eibesfeldt, I. 1961 The fighting behavior of animals. Scientific American
205(6): 112–122.

Lorenz, K. 1963. Das sogenannte Böse, zur Naturgeschichte der Aggression.
Borotha-Schoeler Verlag, Wien.

In July, 1913, I was hunting in the Cove’s River Ranges with
two companions-Andrew and John Duncan, of Megalong.

We found a black-and-yellow banded monitor lizard about five
feet long concealed in a crevice on the face of a wall. We had no
intention of injuring him, but out of mischief Andrew Duncan
suggested that we should make him yell. I was sceptical, but
both men assured me that the lizard could, and would yell under
persuasion. On condition that there should be no cruelty, I con-
sented to a demonstration. They laughed at the idea of cruelty.
Andrew picked up a stick and began poking the reptile in the
ribs and tickling him under the arm. It stood it for a while,
merely squirming closer down in the crevice, then, having had
enough of it, blew himself out and emitted a most comically
doleful bellow that could be heard several hundred yards away.
This he did repeatedly until we had laughed ourselves tired. It
was funny, on looking back after we had gone fifty yards, to see
the lizard stick his head around the corner to make sure that we
had really departed. 

I have had for the last four years at my hunting-box on the
Naltai River, a tame monitor whom I have called “Joseph” on
account of his coat of many colors, and who is the interesting

companion of my solitude and incidentally keeps the snakes
away. With the above in my mind, I experimented on him. I
found him camped under the bench beneath the window, and
irritated him with the end of a stick. He did as the other had
done — filled himself with wind and then emitted it in a pro-
longed bellowing groan. By the way, our “bookbook owl” does
much the same thing. He fills himself nearly to bursting in a suc-
cession of gasps, and then says “Hoo-hoohoo” till he has no
more breath, then fills up again.

EIBL-EIBESFELDT

1 Originally published in Science 52: 273 (1920).

The Booming Lizard of Australia1

Walter H. Bone

Linnzan Society of New South Wales, Sydney

“Black-and-yellow banded monitors” (= Lace Monitors, Varanus varius)
can be loudly vocal when disturbed.

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