A hammerhead shark has a wide head shaped like a hammer. This wide, hammer-shaped head is called the cephalofoil, with a hammerhead's eyes at the two ends of it, where the wide-set eyes give the shark good sight.

Some scientists once suggested that hammerhead eyes are so far apart that their visual fields could not overlap. Others argued that the wide spacing of the eyes actually improves a hammerhead's binocular vision, which means seeing with both eyes at once.

A 2009 study found a 48-degree arc covered by both eyes in the winghead shark, a hammerhead, and a binocular overlap of 34 degrees in the scalloped hammerhead. Because a hammerhead's eyes are widely spaced there is a larger blind area just in front of its snout.

A hammerhead has electrical sense organs called the ampullae of Lorenzini, which are small pores along the underside of its head, and these pores are gel-filled and work as highly sensitive electrical receptors.

Electroreceptors on the underside of a scalloped hammerhead's snout and hammer help it detect buried prey and navigate. In experiments hammerheads detected hidden prey 40% farther from their swimming path than sandbar sharks did. One study reported that the cephalofoil is a better electrosensory detector of hidden prey than a conventional head, sweeping a broad area with no loss in sensitivity. A hammerhead's nostrils have highly sensitive membranes that can pick up even a trace of amino acids in the water.

A hammerhead eats fish, squid and crustaceans such as crabs, and a great hammerhead favors stingrays, groupers and sea catfishes as food. Scalloped hammerheads use their hammer-like head to pin stingrays to the ocean floor before eating them.

The hammerhead's wide head has been hypothesized to give it sensory advantages. A National Science Foundation grant calls the function of the widened head unclear while calling hammerheads one of the most striking examples of evolutionary divergence in form and function. Two theories hold that the hammer head may increase maneuverability and produce lift like a cambered airplane wing, which is a wing with a curved top.

The great hammerhead is the biggest kind of hammerhead shark and can grow to 6 m long but rarely exceeds 4.5 m. The front edge of an adult great hammerhead's head is nearly straight, with a head width of less than 40% of its total length. A scalloped hammerhead has a notch in the middle of the front of its head.

Hammerhead sharks live in warm seas around the world. A great hammerhead lives close to the shore and also far out at sea, although it is often found near reefs and the bottom, in water 1 to 80 meters deep.

Adult scalloped hammerheads dive rapidly and repeatedly from warm surface waters to depths exceeding 800 meters, where the water is as cold as 5 degrees C. A scalloped hammerhead followed for 27 days made more than 76 deep dives at night, the deepest of which reached 964 m, where the water was 5.8 degrees C. The authors of that tracking study said the purpose of the nightly deep diving is unknown. Biologgers, which are recording instruments carried by adult scalloped hammerheads, showed that muscle stayed warm throughout the deepest part of each dive.

Hammerhead sharks living at the oceanic islands of one study could travel more than 40 km on their nightly excursions. In another study tagged scalloped hammerheads moved widely across the Gulf of Mexico continental shelf.

Great hammerheads migrate with the seasons, which means they travel from place to place as the seasons change. In some places huge schools of small migrating scalloped hammerheads move poleward in summer, while two tagged great hammerheads were confirmed pregnant and one of them migrated from the Bahamas to South Carolina.

A mother hammerhead gives birth to live pups, and a mother scalloped hammerhead carries her pups for 9 to 10 months before they are born. Scalloped hammerhead pups live in shallow coastal nursery areas, where young scalloped hammerheads swim together in large schools.

Words to know

• electroreceptors: electric sensors
• biologgers: tracking instruments
• maneuverability: turning skill
• binocular: using both eyes
• nostrils: smelling openings
• hypothesized: suggested