Birds have an astounding variety of bills, or beaks if you prefer. Consider the frogbills, the spoonbills, the crossbills, the boatbill heron, the New Zealand wrybill (a small shorebird whose bill is curved sideways.) Bird tongues, on the other hand, are nowhere near that variable. Most bird tongues are fairly boring. But there are notable exceptions.
Some birds have minor modifications to tongue anatomy that allow them to feed more efficiently. In penguins and mergansers, the upper surface of the tongue is covered with backward-pointing conical papillae that hold slippery fish. Other fisheating divers, the auks, grebes, and loons, have smooth tongues. The tongues of shoveler ducks have serrations and papillae collectively functioning as filters—avian baleen, in a way.
The tongue of flamingoes, with its serrated edges and papillae, is used to sift small food items from soft mud. It’s also unusually large, filling the whole lower mandible, and meaty. Flamingo tongues were a popular item at ancient Roman banquets. Pliny the Elder quotes the Roman gourmand Apicius on the delectable qualities of flamingo tongues, although the only flamingo recipe in my edition of Apicius is for the whole bird; also recommended for parrot. The poet/satirist Martial, as translated by Stephen Jay Gould, speaks for the flamingo: “My red wing gives me my name, but epicures regard my tongue as tasty. But what if my tongue could sing?”
The most baroque of all bird tongues have evolved in the woodpecker family. Supported by extraordinarily long hyoid bones, the tongue wraps around the bird’s tongue and anchors at the base of the bill. Typical woodpeckers have barbs on the tip of the tongue to impale their wood-boring insect prey. The whole apparatus is coated with sticky saliva.
Then there are the nectar feeders, whose tongues seem to fall into two categories: brush-tipped and split. Lories and lorikeets, white-eyes, Australasian honeyeaters, and Neotropical honeycreepers (which I think are now tanagers) all have tongues with brushlike tips. That’s also true of sapsuckers, an aberrant woodpecker genus specialized for feeding on tree sap.
Some of the drepanines or Hawai’ian honeycreepers, including the i’iwi and apapane, have an elaborated version of the brush-tongue, As described by drepanine authority H. Douglas Pratt: “…such tongues look as if a secondary structure has been grafted onto the distal end of a finch tongue. This tubular part of the tongue is formed by narrow laciniae, thread-like projections along the lateral edges of the tongue that arch upward and inward to interlace dorsally forming a tube. Longer laciniae at the tip form a forward-pointing brush.” The extinct o’os of Hawai’i, formerly classified with the honeyeaters but now placed in their own family near the waxwings, are described as having scroll-edged and fringed tongues.
The most specialized nectar-feeders, the hummingbirds and their Old World ecological counterparts, the sunbirds, have long forked tongues with fringes of lamellae. (Lamellae, I gather, are a lot like laciniae.)They were assumed to work by capillary action, but no one bothered to puzzle out the details until recently. Now, thanks to Alejandro Rico-Guevara and Margaret Rubega of the University of Connecticut, we know that it’s more complicated than that.
Rico-Guevara and Rubega used high-speed video cameras to record 30 hummingbirds of 10 different species as they drank from
transparent feeders. What they observed was that when the tongue touches the liquid food source, the two tips are closed and the fringing lamellae are flattened against it. Then the tips separate and the lamellae spread out from each fork. When the hummingbird pulls its tongue out, the tips come back together and the lamellae roll in, trapping the liquid. From that point capillary action takes over, moving the nectar into the throat.
This appears to require no expenditure of energy on the hummer’s part, since the same thing happens mechanically with the tongues of dead birds. “We demonstrate that the hummingbird tongue does not function like a pair of tiny, static tubes drawing up floral nectar via capillary action,” write Rubega and Rico-Guevara. “Instead, we show that the tongue tip is a dynamic liquid-trapping device that changes configuration and shape dramatically as it moves in and out of fluids.” A neat trick indeed, and another reminder of the multiple evolutionary pathways that may lead to the same functional end.
There is a persistent folk belief that the Romans ate hummingbirds’ tongues. Unfortunately for that evocative image of decadence, hummingbirds are found only in the New World. The Romans ate all kinds of things, including roasted stuffed dormice, but hummingbirds’ tongues were definitely not on the menu.