Brian Handwerk
for National Geographic News
October 10, 2007
For centuries insincere humans have been said to cry crocodile
tearsa nod to the famous tale that crocs weep with false remorse
while devouring their prey.
Now research has shown that some reptiles really do shed tears
during a meal, but most likely for biological rather than emotional
reasons
"Generally crocodile tears are pretty similar to human tears," said
study co-author Kent Vliet of the University of Florida.
"You see moisture in their eyes or collecting in the corners of the
eyes. At times it will drip out of the corner and run down their
face just like you'd expect a tear to run down a child's
face."
Of course, there is no "eater's remorse" involved when a croc turns
on the water works.
"Crocodiles appear to produce tears all the time," said croc expert
Adam Britton, founder of the informational Web site
Crocodilian.com.
"Their function islike our own tearsto lubricate the eye. This
may be even more relevant for crocodiles because they have a third
eyelid," also known as a nictitating membrane.
Britton was unaffiliated with Vliet's research, which was published
in the latest edition of the journal BioScience.
Bubbling Tears
Crocodile tears have been difficult to observe because the animals
spend so much time in the water and are too aggressive to be
trained to eat on land.
The University of Florida's Vliet revealed the behavior with
controlled feedings of captive alligators and caimanstwo animals
closely related to crocsthat had become conditioned to eating on
dry land.
The animals were fed a diet of dry, dog-treat-like biscuits, and
they shed tears during most meals.
Some of the reptiles even produced more dramatic foaming around
their eyes.
"At times you can see big bubbles coming up in the corner of the
eye, sort of like soap bubbles," Vliet said.
In crocodiles, Vliet believes the weeping may be a byproduct of
another feeding behavior: the hisses and huffs that crocs make
while dining.
These acts may force air though the reptiles' sinuses, where they
stimulate fluid in the tear, or lacrimal, glands and force them
into the eyessometimes to the point of overflow.
Even simpler explanations could also account for crocodiles'
tears.
"The general contraction of jaw muscles during the bite reflex may
help to squeeze tears out of the lacrimal glands [and] ducts," croc
expert Britton said.
"[Another] explanation is that accumulated tears that well up below
the eye are simply displaced and run down the jaws when the
crocodile moves its head to eat, and it's easy to associate that
'crying' with eating."
In the violent world of crocodiles, tears likely play a protective
role.
"There's a lot of drama going on around the head while they are
subduing prey," Vliet said. He noted that a croc's eyes also recede
into its head as the animal manipulates its mouth.
"They may just be trying to protect the eye."
source http://news.nationalgeographic.com/news/2007/10/071010-crocodile-tears.html
