Brian Handwerk
for National Geographic News
October 10, 2007For centuries insincere humans have been said to cry crocodile tears—a 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 is—like our own tears—to 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 caimans—two animals closely related to crocs—that 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 eyes—sometimes 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
