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Crocodile Eyes Are Designed for Ambush Attacks

The visual systems of crocodiles are more cleverly designed than previously thought, facilitating their ambush hunting techniques and semi-aquatic lifestyles.

Nicolas Nagloo, a PhD student from The University of Western Australia’s School of Animal Biology, explains that crocodiles are excellent predators that quietly wait at the water’s edge before attacking their prey with a burst of speed. “They are experts at ambushing prey while remaining concealed, and their heightened vision plays a big role in this,” Nagloo said. “The water surface makes up the majority of the bottom of the visual field, and the visual horizon occurs along the riverbanks where crocodiles see best.”

While the vision of saltwater and freshwater crocodiles is similar above the water’s surface, the light conditions they experience underwater are significantly different. “In freshwater habitats there is a lot of long wavelength [red] light,” Nagloo said. “In contrast, saltwater habitats have a broader range of wavelengths, providing a greater amount of short wavelength [blue] light.”

Nagloo’s research, published in the Journal of Experimental Biology (http://tinyurl.com/jpb8nrc), compared the eyes of the two crocodile species and found that instead of having a compact fovea (a depression in the retina where there is a high density of photoreceptors that provide a high resolution view of the world), the foveae of saltwater and freshwater crocodiles are stretched across the back of the eye in line with the horizon. “This provides the crocodile with increased visual clarity and the ability to see fine detail without moving their head,” Nagloo said.

Nagloo investigated the sensitivity of different photoreceptors in both species’ eyes, and was surprised to learn that crocodiles have relatively sophisticated colour-sensitive cones. “The sensitivity of the saltwater crocodiles’ colour photoreceptors was slightly shifted to shorter (bluer) wavelengths compared with that of the photoreceptors of the freshwater crocodiles, even though neither species can focus underwater, suggesting they may use their vision underwater more than we have previously thought,” he said. “The subtle difference between the visual systems of the two Australian species gives each an advantage in their environments.”