You don’t have to look at many birds to realize that they are very variable in appearance: hawks look different from hummingbirds, and both look different from peacocks. You can spend a lot of time looking at birds, though, before you realize that they are hiding a lot of variation inside their mouths: long tongues, short tongues, spiky tongues, curly tongues, forked tongues, frayed tongues, brush-like tongues.

Like bird bills, bird tongues are specialized to each particular bird’s way of feeding. Birds that feed on nectar have tongues specifically adapted to nectarivory, often with many little protrusions at the tip of the tongue, giving it a frayed or brush-like appearance. This brushiness increases the surface area of the tongue, making it better at picking up nectar.

Hummingbirds go a slightly different route from other nectarivores. Rather than fraying their tongue into a paintbrush, they split it in two near the tip. That’s right: hummingbirds have forked tongues.

Each half of a hummingbird’s tongue is curled longitudinally. When the tongue is submerged in liquid, the tongue halves partially unfurl; when the tongue is withdrawn from liquid, the tongue halves curl up again. This means that as a hummingbird laps up nectar, it essentially has two tiny straws on the tip of its tongue that open up in the nectar, then curl closed as they are withdrawn, trapping the nectar inside. Even better, the furling and unfurling of the tongue is all due to physical forces, not muscles: the hummingbird doesn’t have to think about its tongue, it just laps up the nectar and physics does the rest (Rico-Guevara & Rubega 2011).

Of course, this wouldn’t work if the hummingbird couldn’t stick its tongue out far enough to reach the nectar. Tongue stick-out-ability is another feature that varies a lot among birds. The champions are nectarivores and woodpeckers.

Woodpeckers need to be able to stick their tongues far out in order to get bugs out of holes in trees. Woodpecker tongues are sharp and spiky, and they use them like little spears to catch and eat their insect prey.

Fish-eating birds also have sharp tongues for hanging on to prey. Birds don’t have teeth, so if they want a sharp implement for handling prey, it has to either be on the bill or the tongue. The tongues of fish-eating birds are often covered in little rear-facing hooks or spikes to prevent a captured fish from slipping away from them.

Penguins take this to something of an extreme, with really spiky tongues. Like many birds, penguins have partially keratinized tongues, meaning that parts of the tongue are made strong and stiff by keratin. (Keratin is in your fingernails, hair, and skin.)

Geese and ducks also have spiky tongues, as well as hairy tongues and tongues with hard flat surfaces. There’s a lot going on in goose and duck tongues. Geese and ducks have tongues that look almost human-shaped from a distance, simply because their bills—into which the tongues have to fit—are shaped a bit like a human tongue, unlike the pointy bills of most birds. But if you get up close, you’ll realize that your tongue looks nothing like a goose’s.

Hairs and spikes on the duck/goose tongue act like a sieve, allowing the bird to filter food particles from the water, somewhat like a baleen whale. The tongue can also be used to grip food: geese eating grass hold onto the grass by pressing it between the tongue and the top of the mouth.

Flamingos also use hairs on their tongues to filter-feed.

Not all birds have extremely specialized tongues. Songbirds generally just have triangular, not-too-crazy tongues, although they may have some small spikes or hairs to help them hold onto insects.

Raptors, too, have fairly simple tongues, with some small spikes or hairs to help hold onto prey.

Shorebird tongues are so covered in tiny hairs that they have a “velvety” texture (Elner et al. 2005).

Parrot tongues are used to manipulate their food inside their bill. Although their tongues may look unimpressively blobby, parrots are unusual among birds in having muscles in their tongue, like we do. Most birds don’t have muscles in the front third of their tongue at all.

The most rudimentary bird tongues are those of the ratites: flightless birds like the ostrich, emu, rhea, and kiwi. Ratite tongues are small and triangular and don’t reach the tip of the bill. They don’t seem to be involved in catching or manipulating food. And—I am sure you have always wanted to know this—the North Island Kiwi’s tongue’s “large laryngeal pad… incidentally, is very similar in outline to the swim-bladder of the porcupine-fish!”

I did not add that exclamation point; that exclamation point is quoted, along with the rest, from McCain (1973). But hey, can you blame him? Tongues are pretty exciting.

References:

Elner RW, Beninger PG, Jackson DL, Potter TM. 2005. Evidence of a new feeding mode in western sandpiper (Calidris mauri) and dunlin (Calidris alpina) based on bill and tongue morphology and ultrastructure. Marine Biology 146:1223-1234.

Erdogan S, Iwasaki S. 2014. Function-related morphological characteristics and specialized structures of the avian tongue. Annals of Anatomy 196:75-87.

McCain C. 1973. The tongues of kiwis (Apteryx spp.). Notornis 20:123-127.

Rico-Guevara A, Rubega MA. 2011. The hummingbird tongue is a fluid trap, not a capillary tube. Proceedings of the National Academy of Sciences 108:9356-9360.

*Photos obtained from Flickr and used via Creative Commons. Many thanks to these photographers for using Creative Commons!