Why Do Elephant Seals Have Big Noses? The Proboscis Explained

What is an elephant seal’s proboscis?

The proboscis is a greatly enlarged nasal chamber that sits on top of the male’s snout. In an adult northern elephant seal bull it hangs over the mouth by about 20 cm (8 in), according to NOAA Fisheries. It is soft and inflatable: when a bull is excited or threatening a rival, the nose swells and lifts, and its tip can drape down toward the open mouth.

The nose starts to grow when a young male is about two or three years old and keeps getting bigger until he is about eight or nine. At the same time he develops a thick, calloused shield of skin across his neck and chest. Females and pups never grow a proboscis, and their noses look like those of other true seals. The southern elephant seal has a proboscis too, but it is shorter than the northern bull’s, even though southern bulls are heavier.

A built-in loudspeaker for threat calls

During the winter breeding season, bulls spend much of their time warning one another. A calling bull rears up on his front flippers, throws his head back, inflates his nose and opens his mouth wide. The result is a deep, rhythmic series of pulses that carries across a crowded beach and is often compared to a drum, a motorbike engine or slow handclaps.

NOAA Fisheries describes the inflated nose as a resonating chamber for these threat calls. The sound itself is produced in the throat, and scientists still debate exactly how much the trunk shapes it. What is clear is that the call and the nose work together as a display: a large, swollen proboscis and a booming voice both advertise an older, heavier and more experienced male. This kind of warning matters because real fights between bulls weighing up to 2,300 kg (5,100 lb) are exhausting and can cause serious injuries.

Rivals learn each other’s voices

Research at Año Nuevo in California has shown that bulls know their rivals by voice. Each adult male has his own call, with a distinctive rhythm and tone quality. In playback experiments, researchers played recordings of particular bulls through loudspeakers. Lower-ranking males tended to back away from the calls of males that dominated them, but reacted quite differently to calls from weaker rivals.

A 2017 study by Nicolas Mathevon and colleagues found that males pay attention to both the tempo of the pulses and the timbre, the tone of the voice. When the researchers changed the rhythm of a call, males responded less strongly, which suggests they had memorized the exact pattern of each rival’s voice. Remembering who beat whom saves energy and injuries: a male who recognizes a stronger bull can retreat without testing him again.

The nose in harem battles

On a busy beach, bulls form a ranking. The top male, often called the alpha bull, stays among the largest group of females and drives off any male that comes too close. Many challenges end with posturing and calls alone. When two well-matched bulls do fight, they rear up chest to chest, slam their necks together and bite, and the thick chest shield takes most of the damage.

Size and age matter more than anything else in these contests, and the proboscis grows along with both. That makes it an honest signal that is hard to fake: a young male cannot grow a full-sized nose before he is old and large enough to carry it. Only a minority of bulls ever win a place with the females, and the most successful father most of the pups. How big these bulls get is described in How big is an elephant seal?

Does the nose help elephant seals save water?

Elephant seals face a water problem. Bulls fast on the beach for up to three months and females for about five weeks, without eating or drinking. Every breath they exhale carries away water vapor.

Inside the nose, elephant seals have thin, scroll-shaped bones called turbinates covered in moist tissue. As warm air from the lungs flows out over these cooler surfaces, much of its water condenses and is reabsorbed. Studies on northern elephant seals in the 1980s showed that this nasal heat and water exchange saves a significant amount of water over a long fast.

These inner nasal passages work in both sexes and in young seals, though, so water saving is not why only males grow a trunk. The male’s external proboscis is best explained as a tool for competing with other males.

Other animals with eye-catching noses

Elephant seals are not the only animals whose noses help with displays. The male hooded seal of the North Atlantic can inflate a black hood on top of its head and blow a red, balloon-like membrane out of one nostril when threatened or courting. Male proboscis monkeys of Borneo grow large, drooping noses that appear linked to louder, deeper calls.

Many other marine mammals rely on sound to settle disputes. Sea lions bark to defend their spots on crowded beaches, as explained in Why do sea lions bark?, while elephant seals rely on their roars and their noses. For more about the species, its diving and its migrations, see the northern elephant seal profile.