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M32

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ZOOLOGICAL SERIES

OP
FIELD MUSEUM OF NATURAL HISTORY

Volume XX CHICAGO, MAX 15, 1935 No. 9

NOTES ON THE BREEDING BEHAVIOR
OF LIZARDS

BY KARL P. SCHMIDT

ASSISTANT CURATOR OF AMPHIBIANS AND REPTILES

In the course of the Crane Pacific Expedition of Field Museum,
in 1928-29, opportunity was presented f,pr occasional brief observa-
tions on the habits of amphibians and reptiles. Recent detailed
studies of the breeding behavior of lizanjs by G. K. Noble of the
American Museum of Natural History h^ve proved extraordinarily
interesting and have focused attention on this field.1 At Dr. Noble's
request, I have drawn up the following account of my scattered
observations, which are little more than suggestive leads, but which
happen to include notes on two species of lizards of more than
usual interest — the Marine Iguana, Amb.lyrhynchus cristatus, of
the Galapagos Islands, and the Flying Lizard of Celebes, Draco
spilopterus.

BREEDING BEHAVIOR OF THE MARINE IGUANA

During our stay in the Galapagos Islands, I had some opportunity
to observe the breeding habits of the Marine Iguana, Amblyrhynchus
cristatus, well known as one of the principal zoological peculiarities
of the archipelago. Mr. Walter A. Weber, Mr. Frank C. Wonder,
and I spent the four days from January 7 to January 10, 1929, at
Mangrove Point on the east coast of Narborough Island. This situ-
ation was reached by launch from Tagus Cove on the opposite coast
of Albemarle Island, where our yacht, the Illyria, lay at anchor.

The feral cats and dogs which are the persistent enemies of all
the native animals of Albemarle are happily absent on Narborough,
and this may be one reason for the notably greater number of
Marine Iguanas on the latter island. The shelving plates of glassy
lava which form the shores of Narborough are in any case a favorable
habitat for the marine lizards, which rarely go more than forty or
fifty feet inland.

'G. K. Noble and H. T. Bradley: The Mating Behavior of Lizards; Its Bear-
ing on the Theory of Sexual Selection. Ann. N. Y. Acad. Sci., 35, pp. 25-100, 1933.

No. 338 71

72 FIELD MUSEUM OF NATURAL HISTORY — ZOOLOGY, VOL. XX

At our landing place at Mangrove Point there were about seventy-
five Marine Iguanas within a space thirty feet square. The lizards
lay in the hot sun, some sixty females and young massed together,
often piled one on top of the other three deep, about thirty feet from
the water's edge. The old males, much larger than the largest
females, were scattered over the area between the massed lizards
and the water, spaced from five to ten feet apart, each one keeping
to his own sunning territory.

Trespass on the sunning terrain of a large male by another was
invariably the occasion for a fight. Fighting was carried on by
butting, each contestant endeavoring to get the rough horny knobs
on his forehead beneath his opponent's chin. Injury to the lips
from the butting knobs was made very evident by the appearance
of blood in the puffs of spray emitted at intervals from the nostrils.
The fights continued until the weaker contestant was driven off,
whereupon the winner resumed his sunning position, or advanced
toward the females. One pair of males engaged in combat across
a deep crack in the lava, into which they fell as the fight progressed.
The longest fight observed lasted for four minutes. The larger size
of the males and their shortened massive heads, with heavy forwardly
directed horny spines, appear to be correlated with this fighting habit.

The breeding season was apparently at its height at the time of
our visit. Copulation was twice observed. In each case the male
approached the massed females with a curious strutting gait, nodding
his head and blowing jets of spray from his nostrils. Reaching a
position parallel with an isolated female, he grasped her by the fold
of skin at the nape of the neck, straddled her, and dragged her
about over the rock, the female's legs hanging limp. This dragging
was continued for a half minute in one case and for a full minute
in the second. Copulation followed immediately upon this rough
courtship, the tail of the male being curved beneath that of the
female and one hemipenis inserted while the tail of the female was
raised and curved over that of the male. In one case the hemipenis
was everted before insertion. Copulation lasted about one minute
in one case and two in the second, but both pairs were disturbed, one
by a sea-lion, and one by another male iguana.

The large aggregations of individuals conspicuous on Narborough
were not to be found at Tagus Cove on Albemarle Island, nor at
South Seymour Island, nor at Academy Bay or Conway Bay on
Indefatigable. At Conway Bay Marine Iguanas were found to be
assorted in family groups composed of a single large male with from

1935 BREEDING BEHAVIOR OF LIZARDS— SCHMIDT 73

i

FIG. 4. Courtship of Marine Iguana, Narborough Island.

FIG. 5. Mating posture of Marine Iguana, Narborough Island.

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MAY 3

"RSITY Of ILL;

74 FIELD MUSEUM OF NATURAL HISTORY — ZOOLOGY, VOL. XX

two to four females, these groups separated by twenty to fifty
yards of shore-line without iguanas.

These observations indicate that a simple form of polygamy is
normal to the Marine Iguana when the population is small and
sparse, and that when the concentration of individuals is greater,
promiscuous polygamy replaces the simpler form. The massed
sunning females on Narborough form a joint harem for the adjacent
group of sunning males. It is evident that this curious lizard offers
an especially interesting subject for further and more detailed
observation, and that a complete study of its life history will con-
tribute important information in the general fields of animal behavior
and animal aggregation.

COURTSHIP OF SKINKS

During a casual visit to the cottages of Mr. Zane Gray, on the
island of Tahiti, my attention was attracted to the abundance of
the small skinks, Ablepharus poecilopleurus, in the brilliant sunshine
on the roofs and gables of the buildings. The numerous crevices
afforded by the clapboard siding where it was overlaid by the
diagonal boards beneath the gables were used as retreats by
the lizards. While I watched one of these lizards climb slowly toward
the peak of one of the houses, another individual rushed out upon
it from a crevice, grasped the first one by the neck, and shook it
with the utmost violence. Thinking that an unequal combat between
two males was in progress, I was surprised to see the violent shaking
immediately followed by copulation, which continued for at least
half a minute. Although the observations of Noble and Bradley
show that verification of the sex of the passive individual is necessary,
it seems likely that this is the normal breeding procedure in this
species.

NUPTIAL DISPLAY IN FLYING LIZARDS
The rather open forest on the steep slopes of Lembeh Island, off
the extreme northeastern corner of Celebes, presented an unusual
opportunity to observe flying lizards. This was the only place where
we saw these creatures near the ground and in great abundance.
In Borneo, on flat terrain, we did not obtain or see a single specimen.
In the Philippines a species of flying lizard was observed in coconut
plantations near Zamboanga. Observation of these creatures is
favored when they occur on steep slopes, since the observer can be
at the level of the lizards when these are well up on the trunks of
trees situated below his station. This was notably the case on

1935

BREEDING BEHAVIOR OF LIZARDS — SCHMIDT

75

FIG. 6. Courtship display of Celebes Flying Lizard, Lembeh Island, Celebes. From painting by
Walter A. Weber.

76 FIELD MUSEUM OF NATURAL HISTORY — ZOOLOGY, VOL. XX

Lembeh Island, where Draco spilopterus, the common species of
this genus in Celebes, is especially abundant. No flying lizards
were observed at this locality until, on the last two days of our
stay (June 21 and 22, 1929) sunshine succeeded the previous cloudy
and rainy weather.

On these days Draco spilopterus was abundant in the rather open
hardwood forest which clothes the slopes of Lembeh. The longest
glide observed was perhaps thirty feet, there being no occasion for
longer flights. These lizards glide at a low angle and alight without
shock after 'only a very slight upturn. Mr. Walter A. Weber, the
expedition artist, and I were fortunate in witnessing what appeared
to be the courtship display of these lizards. A female, with wings
folded at her sides, clinging head upward on a tree trunk a dozen
feet distant from our station and twenty feet from the ground, was
approached from above by a male, who advanced to within a few
inches of the female, halted, and went through bobbing motions like
those familiar to American herpetologists in the genus Anolis. As
the anterior part of the body was raised, the colored dewlap was
distended to its fullest extent, and at the same time the brilliantly
colored wings were extended to the greatest possible degree. In this
posture the bobbing display was continued for perhaps a minute.
At this juncture a second male flew from a tree near us to the tree
on which the courtship was in progress, ran up the tree and engaged
the first male in combat. This struggle was so violent that both
animals fell from the tree. They disengaged in mid-air, and sailed
off to separate trees. The recovery of balance in mid-air and the
ability to direct the flight to a suitable landing place is an interesting
testimony to the perfection of gliding flight attained by these lizards.

Whether the bobbing motions and display of the colored wing
and throat membranes are for the attraction and excitation of the
females or solely for sex recognition, it seems clear that the brilliant
coloration of the wings is correlated with this secondary use. There
is even the interesting possibility that these unique structures
originated as a secondary sex character, and that their use in gliding
flight is secondary. More detailed observation and well-planned
field experiments on Draco like those of Noble and Bradley on the
American fence lizards might be especially illuminating for the
problems of lizard courtship behavior.

Our attempts to obtain a photographic record of Draco spilopterus
were failures. Mr. Weber has embodied our joint observations in
a painting, here reproduced.

UNIVERSITY OF ILLINOIS-URBANA