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Boana
rosenbergi |
Gladiator
Tree Frogs are common inhabitants of the humid lowlands in central
and southwestern Costa Rica. These large tree frogs may measure
anywhere from 70 to 90 millimeters and are easily distinguished by a
pencil thin line that runs from the tip of their snout to the middle
of their back.
A close inspection of their
hands will also reveal a prepollex spine that protrudes
next to their thumbs, which is of vital importance during their
reproductive cycle.
Gladiator Tree Frogs spend
most of their lives in the tree tops. This is where they rest during
the day and where they spend the driest part of dry season.
During their breeding season
males descend from the
canopy to marshy areas.
There they excavate a nest which may measure between 100 and
300 millimeters in diameter. Once the nest is completed and fills
with water, the male jumps in the nest and begins to call out to the
females.
Their call is
very distinctive and could be described as low hammering on a hollow
log. |

If a female is attracted by
the call, she will
approach the calling male and enter his nest. As she is approaching,
the male starts a courtship call which has a lower intensity
than his advertising call.
While the male is engaged in his
courtship call, the female inspects his nest to see if it meets
her criteria. Studies have shown that females have high standards
and usually reject the male and his nest about fifty percent of the
time!
During the inspection, the female
may frequently bump the male. If she
really likes the nest, she will give the male a full body massage! The male
will then mount the female in axillary amplexus, as shown in the
photograph below. |
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Once in amplexus, the female
may spend up to 3 hours renovating the nest! She may lay over 3000
eggs in total.
This
process takes about 10 minutes. The eggs float on the surface of the
water and normally hatch within two or three days.
During this
time, the parent male patrols and aggressively guards his nest site.
Given the chance, rival Gladiator Tree Frog males may jump in the
nest. Such an attack would have disastrous repercussions, breaking
the nest's surface tension and causing the eggs to sink and drown.
It is during these crucial hours, while their eggs are developing,
that Gladiator Tree Frogs really live up to their name and
reputation. |
If
an intruder is detected nearby, a series of territorial and
encounter calls are emitted by the parent male. These may include
chuckles, hisses, mews, barks and growls. If the intruder is
undeterred, the parent male will try to chase him away or tackle him in
order to keep the dead beat male away from his nest.
Once the conflict gets physical, it
can quickly turn brutal.
Battling males use their prepollex spines as weapons and immediately attempt to gouge out their opponent's eyes and break
their eardrums. These duels will often result in permanent damage to
the frogs and the battle may ensue until one of them has been
killed. Studies have shown that most male frogs suffer permanent
damage during mating season.
If the parent male is successful
in protecting his offspring, and they manage to hatch, it may take about 40 days for the tadpoles to complete their
metamorphosis.
When they emerge from the water, still sporting their tadpole tail,
they are covered with small dark spots. |
The individual featured here was photographed in Drake Bay.
Gladiator
Tree Frogs are only known to exist in Costa Rica, Panama, and parts
of Ecuador and Colombia. |
References:
Leenders, T.
2001 A Guide to Amphibians and Reptiles of Costa Rica
Zona Tropical
Savage, J. 2002 The Amphibians and Reptiles of
Costa Rica University of Chicago Press
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The Frog
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