By Dr. Becker
Crocodiles are one of the world's greatest ambush predators. They lack the endurance for long chases on land or in the water, so instead they depend on launching surprise attacks on their prey.
Crocodiles lie in wait, camouflaged in the water, until an opportunity presents itself. These indiscriminate eaters will attack virtually anything for a meal — zebras, hippos, birds, porcupines, fish, crabs, small mammals and even people are all fair game for a crocodile.
At the first glimpse of a meal, the crocodile explodes into action, lunging for and typically catching its prey in one swift movement, often before the prey has a chance to react.
Crocodiles are believed to be largely unchanged from their prehistoric ancestors (dinosaurs), but they do have some unique features that make them remarkably adept at their sneak attacks. Recent research shows even their eyes are fine-tuned for lurking.
Crocodile Eyes Are Uniquely Suited for Lurking
Crocodiles lie in the water seemingly motionless, which is a key part of their hunting strategy. They stay so still that they blend in easily with their environment and unsuspecting prey may swim right by. Their eyes are uniquely suited for this long-term lurking.
Research published in the Journal of Experimental Biology found crocodile eyes have a horizontal streak of tightly packed receptors called fovea.
The fovea are typically located in a circular area, but in crocodiles the horizontal streak gives them the advantage of being able to scan the shoreline for prey without moving their head.
Fovea are used for high-resolution viewing. In humans, for instance, we use fovea to read, but because the fovea only exist in a small area, we must move our eyes to see larger areas. Nicolas Nagloo, study author and Ph.D. student at the University of Western Australia, told BBC News:1
"Typically, the fovea is circular and located in the center of the retina. It provides animals with an area of very high visual clarity, in a small area of their visual environment …
In the case of crocodiles ... it's spread across the middle of the retina, and it gives them maximum clarity all along the visual horizon."
Overall, it's believed that crocodile vision is up to seven times less precise than human vision, but the high-clarity "foveal streak" gives them a strong advantage in finding prey.
Crocodile Eyes Are Adapted for Different Water Conditions
Other unique features were also noted in crocodile eyes, specifically in relation to their salt and freshwater habitats. Saltwater tends to have more blue light while freshwater has more red light.
The study found that crocodile eyes corresponded with their habitat's lighting conditions; freshwater crocs were more sensitive to redder wavelengths of light than saltwater crocs.
The finding is especially intriguing because crocodiles have blurry vision underwater, and it wasn't thought vision was an important sense for them while swimming. Nagoo told BBC News that this assumption may need to be investigated:2
"It's surprising because these guys can't actually focus underwater. [But] light sensitivity seems to be important to them … That tells us there's potentially some aspect of their behavior underwater that we're not aware of yet."
Do Crocodiles Hunt in Groups?
Whether or not other species engage in this seemingly rare behavior is unknown, in large part because it's difficult to observe animals hunting in their natural environment.
This is especially true of crocodilians (crocodiles, alligators, caimans and gharials), as they typically hunt at night in murky waters in remote swamps and rivers. Further, they eat infrequently, which makes witnessing hunting efforts even more challenging.
Dr. Vladimir Dinets of the University of Tennessee in Knoxville used a combination of eyewitness accounts from amateurs and researchers, 3,000 hours of observations and diary accounts dating back to the 19th century to learn more about crocodilian hunting behaviors.3
What he uncovered is that most of the observations had a common thread — crocodiles (and alligators) appear to use coordination and collaboration when hunting their prey.
Crocodiles have been observed swimming in circles around fish in order to force them into a tight "bait ball" and then taking turns swimming through the bait ball for a snack.
In another instance, a crocodile on land scared a pig into a lagoon where two other crocodiles were waiting in ambush. Crocodiles have also been known to chase fish toward shore where smaller crocodiles were waiting. Dinets told Science News:4
"All these observations indicate that crocodilians might belong to a very select club of hunters — just twenty or so species of animals, including humans — capable of coordinating their actions in sophisticated ways and assuming different roles according to each individual's abilities. … In fact, they might be second only to humans in their hunting prowess."
Do Crocodiles Live in the US?
American crocodiles are considered an endangered species. The only remaining American crocodiles in the U.S. live in southern Florida, while most others are found in Mexico, Central America, the Caribbean and South America.5
Habitat loss, illegal hunting and roadkill present serious threats to American crocodiles. The Nile crocodile, found in Africa, is also facing population declines due to pollution, hunting and habitat loss.6 In case you were wondering, you can distinguish a crocodile from an alligator by the fourth tooth on the bottom of the jaw; it's visible on crocodiles when their mouths are closed.7