Morley Read / Map treefrog (Boana geographica) blinking, Amazon rainforest, Orellana Province, Ecuador. (non-ex)

Morley Read / Clown treefrog (Dendropsophus reticulatus) closing its eyes, Amazon rainforest, Orellana Province, Ecuador. (non-ex)

Morley Read / Leaf frog (Cruziohyla craspedopus) blinking its eyes, Amazon rainforest, Napo Province, Ecuador. (non-ex)

Jack Dykinga / Raven (Corvus corax) with nictitating membrane over eye, in a blizzard on Hurricane Ridge, Olympic National Park, Washington, USA. Sequence 2/2

John Waters / Common European toad (Bufo bufo) at surface, retreats underwater, Priddy, Somerset, England, UK, April.

Eric Baccega / Shoebill stork (Balaeniceps rex) portrait with a closed eyelid. Swamps of Mabamba, Lake Victoria, Uganda.

Jordi Chias / Whale shark (Rhincodon typus), closing nictitating membrane, South Ari Atoll, Maldives Islands, Indian Ocean.

Nick Upton / Rook (Corvus frugilegus) calling while perched in a Willow tree and blinking to show its blue nictitating membrane, Gloucestershire, UK, February.

Dave Bevan / European common frog (Rana temporaria) in a pond, closing its nictating membranes to lubricate its eyes, Carmarthenshire, Wales, UK, February.

Ingo Arndt / Spurell's Flying Frog (Agalychnis spurelli) eye closed with semi-transparent eyelid that allows it to see its surroundings even while resting, Costa Rica.

Juan Carlos Munoz / Bateleur eagle (Terathopius ecaudatus) portrait with nictitating membrane closed, Captive, occurs in Africa.

Richard Robinson / Blue shark (Prionace glauca) with nictitating membrane partially shut to protect its eye, Hauraki Gulf, Auckland, New Zealand, June.