Walruses are large marine mammals inhabiting the Arctic, known for their prominent tusks. A common observation is the reddish tint their eyes sometimes display. This appearance is a natural physiological characteristic, reflecting biological adaptations that enable them to thrive in their challenging environment.
The Science Behind the Red Appearance
The reddish appearance in a walrus’s eyes is primarily due to an extensive network of blood vessels surrounding and within the eye structures. The sclera and conjunctiva contain numerous capillaries. These tiny blood vessels become more visible, giving the eye a reddish hue, when blood flow to the area increases. This increased vascularization serves several biological functions.
When blood vessels in the eye area are engorged, the capillaries become more prominent near the surface, similar to how a person’s skin might flush when warm or exerting themselves. Walrus eyes possess a thick layer of blood vessels between the sclera and the retina, which likely plays a role in temperature regulation. Insulating, fat-rich connective tissue and many blood vessels around the eye further support its function in cold conditions.
Environmental and Behavioral Influences
The environment and specific behaviors of walruses can intensify the red appearance of their eyes. Thermoregulation is a significant factor. When active, such as after foraging or during exertion, or in warmer conditions, increased blood flow is directed to surface tissues, including around the eyes, to dissipate excess heat. This helps regulate their body temperature.
Changes in blood pressure and flow during and after deep dives also contribute to the prominence of blood vessels in the eyes. Walruses can stay submerged for up to 10 minutes and dive to about 80 meters to forage for bottom-dwelling prey. The redirection of blood flow during dives, and its subsequent return to surface tissues, can make the eye’s vascularity more evident. External light conditions also play a role, as bright sunlight or reflections off ice and snow can make the underlying redness more noticeable.
Walrus Eye Adaptations for Their Habitat
Walrus eyes exhibit several adaptations tailored to their Arctic habitat. Their eyes are small and specialized for short-range vision, particularly underwater. Walruses can protrude their eyes for a wider visual field, and retract them deep into the orbital cavity for protection from injury and warmth in freezing waters.
Walrus eyes are adapted for dim conditions, both in murky water and during long polar nights. Their pupils adjust to varying light levels, appearing as a vertical oval in low light, keyhole-shaped in moderate light, and pinhole-shaped in bright conditions. A reflective layer behind the retina, the tapetum lucidum, enhances light sensitivity, aiding vision in dim environments. Walruses also possess a nictitating membrane, a translucent third eyelid that sweeps horizontally across the eye, providing protection against cold, ice, and debris while maintaining some visibility.