Getting the Bill – Taste, Touch and Smell in Birds
One of the defining characteristics of birds, besides the obvious features of wings and feathers, is their bills. And they come in a wonderful smorgasbord of different shapes and sizes. From toucans to curlews and from hummingbirds to flamingos, birds display an almost otherworldly diversity in these body-parts. Bills are instrumental in defining three of the senses in birds – taste, touch and smell. But how birds use these different senses, like the diversity in bill size and shape, varies almost as much from species to species.
The longest bird bill relative to body-size. Sword-billed Hummingbird, Colombia
Bills come in all shapes and sizes. Pale-mandibled Aracari by Luke Seitz
Taste, touch and smell in birds are generally considered to be weaker than these same senses in mammals. Let’s talk about taste. Whilst catfish have around 100,000 taste buds, rabbits around 17,000 and humans approximately 9,000, birds rarely exceed 100 of these receptors. Chickens come in at around 24, pigeons have around 40-50 and some duck species may have a whopping 400. But the mere existence of taste buds, albeit in limited quantities, seems to suggest that most birds have the ability to at least distinguish between sweet and sour and salty and acidic.
This African Green Pigeon may have a mere 50 taste buds Adrian Binns
When it comes to smell, there is also great variation amongst bird species. Most appear to have a very limited sense of smell and mammals appear to have better developed olfactory glands. But certain bird species go against the grain here and some even appear to have a better sense of smell than many mammals, humans included. Honeyguides, for example, are strongly attracted to the smell of wax. A Dominican missionary in Mozambique in the 16th century was astounded to find honeyguides eating the wax from his altar candles! And more recent studies have shown that honeyguides can detect even well-hidden beeswax candles.
A Green-backed Honeybird by Markus Lilje courtesy of Rockjumper Birding Tours
In the open oceans of the world, certain species of seafaring birds like albatrosses, petrels and shearwaters have very well developed olfactory glands. Aptly called the tube-nosed birds, on account of their raised and highly visible nostrils, these species are able to hone in on oceanic food from several miles away, based on smell alone. Following oceanic surface smells that are carried by winds, they are often able to locate valuable food sources – like krill and zooplankton. These smells act like olfactory beacons in the massive watery expanse of the open oceans. Many of these same seagoing bird species nest in large colonies, often returning to their nests at night when their vision is compromised. New studies are beginning to show that smell may be an important part in these birds finding the right nest and/or partner under cover of darkness.
White-chinned Petrels are tube-nosed birds Adam Riley
Unlike all other birds which have nostrils at the base of the bill, the kiwis from New Zealand, have them located at the bill tip. Other long-billed birds locate their food by touch and we’ll get to that. But kiwis actually sniff out their food by probing their long bills into the soil and smelling for earthworms and other delectables. This is particularly useful for a bird with small eyes that hunts under the soil surface at night.
A Little-spotted Kiwi by David Shackleford
And then there are the vultures. I remember watching a David Attenborough episode once where he tested the theory that new world vultures could locate carcasses by smell alone. He hid a smelly carcass in some particularly thick forest and, sure enough, the vultures found the putrid prize, even when it was blocked entirely from their view. Like the tube-nosed birds, new world vultures detect the smells of rotting meat carried by the winds. In fact, their incredible smelling ability has even been used by engineers to detect leaks in pipelines by pumping simulated carcass smells into the pipes and then monitoring where the vultures gather!
Turkey Vultures have an exceptional sense of smell Corey Finger
Bills in birds are also very sensitive to touch. And again, there is great variation amongst different species. Ducks are the avian leaders of bill touch. Birds use rectal bristles (at the base of the bill) and tiny touch factories called Herbst corpuscles to detect touch. Herbst corpuscles from the bill of a duck are incredibly elaborate, with up to 12 onion-like layers of touch lamellae. Herbst corpuscles are also found in abundance in the sensitive bill tips of shorebirds like sandpipers. In fact, certain shorebirds like snipes, can actually bend certain sections of their bills. For those of you that are into ancient languages or ridiculous words, the actual term for this is “rhynchokinesis” from the Greek meaning “move snout”. When snipes detect prey, the upper mandible bends upwards, allowing the bill to open. By opening various parts of the length of the bill, the prey can then be shifted upwards from the bill tip to the mouth. Other birds that feed almost extensively by touch include many species of storks, spoonbills, skimmers and shorebirds. The Herbst touch receptors found in bills can also be found in the tongues of many birds and this may aid birds like hummingbirds and woodpeckers that use their tongues extensively in foraging.
A Black Skimmer fishes with its uniquely adapted bill loaded with touch receptors
Taste, touch and smell in birds may be the weaker of the senses when it comes to the majority of birds but this is not a cut-and-dry statement and many species exhibit remarkable developments in one or more sensory fields. One thing is without doubt – birds have a suite of senses superior to our own. We only need to mention the words “navigation” or “migration” to realize that birds may just possess other senses that we can only dream about…