books - Desert Magazine of the Southwest

All this interest in these small-tomedium-sized
lizards is not due to their
reluctance to cooperate. It is mainly because
they are such a successful species
throughout the Southwest, a fact that
points to their great ability to adapt to
many different environmental conditions.
Members of the Urosaurus clan are
daytime operators and make their living
catching insects and other arthropods.
Equipped with excellent eyesight and an
auditory set-up most sensitive in a range
between 700 and 2,000 hertz (fine for insect
sounds) they hunt by sight and
hearing.
Being reptiles they are active in the
warm seasons of the year, depending on
the sun to warm them; depending, too,
upon behavioral tactics to regulate their
temperature, going underground when it
is too hot or too cold. Wintertimes they
become dormant, with perhaps as many
as 30 or 40 clumped together in a retreat
not far from the surface. When spring
rolls around again they appear topside
once more and in due time the big social
season gets underway.
Now since the way an individual gets
along and how local populations keep up
the old numbers are basic measures of
species success, a study of lizard behavior
becomes of first importance. So
zoologists Carpenter and Grubitz, collecting
six adult males and two adult females,
marked them with paint of
various colors for quick identification
and let them loose in an enclosure with
concrete block and logs to climb on.
Then they sat back to watch what happened
in Urosaurus social circle.
The lizards had scarcely been installed
Above:
Urosaurus
ornatus is one
of several
tree-climbing
lizards.
Right: His
cousin, U.
Microscutatus
or smallscaled
brush
lizard, is
found in Baja
California.
Photos
courtesy of
San Diego
Zoo.
Desert/May 1977 37
in their new surroundings before it became
obvious what was first on the
agenda: deciding which male was going
to be the top lizard. There were six males
and therefore six candidates. Each one
was determined, climbing up on the
highest thing he could find and challenging
the nearest male. This "display"
challenge, it turned out, is always done
in the proscribed Urosaurus ornatus
manner: compress the body laterally;
thereby exposing a full side view of the
brilliant blue belly, push out the throat
into a handsome blue or green dewlap,
and when as big and tough looking as
possible, start doing a series of pushups.
All four legs are involved, hoisting the
whole body, head and tail up and down,
the lizard standing tall at the height of
the pushup. In no time at all displaying
males were all over the place, breaking
into chases and fighting, and thereby
sorting themselves out, certain ones
fleeing in retreat, or flattening out in
submission.
Shortly the contestants were down to
two, one marked with white paint, the
other with red. Both were active in displaying
and making overtures to the
ladies but within a few days "whitey"
succeeded in overcoming "red" and this
settled the matter. He now dominated
the whole enclosure doing all the displaying,
and of course, the subsequent
courting of the females. Not one of the
other males, "red" included, displayed.
At this point, to make things interesting,
Carpenter and Crubitz removed
"whitey" and shortly "red" took over,
challenged only briefly by "green." Old
Red turned out to be quite a despot and
inside of a couple of weeks had worked
himself up to some 48 displays an hour,
the rest of the males tearing for cover at
the sight of him. So the zoologists
yanked him, and "green" became dominant
for a few days until "red" was returned
to the scene. War was declared
instantly but eventually "red" became
dominant and ruled supreme.
The thing that was immediately apparent
was that the male (no matter
which one), normally brown on the back,
became very much darker in taking over
the dominant role, and all the subordinate
males paled to a very light brown.
But when the dark dominant was
plucked out and put by himself, he
became lighter in a couple of hours.
Returned and eventually dominant once
more, he became very dark again. This
color change, probably related to the
male's psychological state, reinforces
the effect of his dominance. A dark,
puffed-up, blue-bellied lizard, with extended
colorful dewlaps and doing
;aggressive display pushups vigorously,
is a sight to behold — particularly when
the next move is bound to be a chase and
fight.
Biologists view all this aggressive behavior
and dominance as part of the establishment
and maintenance of territory
under normal conditions. In nature
it acts to distribute the males throughout
the habitat. With elbow room and
territory thus allocated, fighting is cut to
a minimum and the population can settle
down into the business of daily living
and keeping up clan numbers.
Interesting enough, the pushup bit
may have more to it than being just part