For the Birds Radio Program: Salivary Glands
February is Dental Health Month, when Laura Erickson’s thoughts naturally turn to the salivary glands of birds. 3:23 (Date confirmed)
Last week I went to the dentist, the one place where I am always aware that I have salivary glands. In my normal day-to-day life, my salivary glands just sit around quietly, simplifying my food chewing but not doing much else. At least, I assume that they don’t. I don’t usually pay them much attention. But the moment I sit in a dentist’s chair, I can barely open my mouth before my salivary glands erupt, spurting spit at the hygienist or dentist as if I were armed with a hidden squirt gun, and making me wonder about the salivary glands of birds.
Most birds have three sets of major salivary glands and some smaller subsidiary salivary glands to boot. Birds don’t chew their food, so they don’t usually need to start the digestion process in the mouth the way we mammals do, though in seed-eating birds, the salivary glands produce an enzyme that attacks starch molecules. Salivary glands in birds have other purposes. They’re very reduced in most water birds, like sandpipers, gulls, and loons, whose food is wet to begin with so they don’t need to lubricate it to get it down the throat. But for some reason, ducks and geese have well-developed salivary glands. They’re most well-developed in woodpeckers, where they produce two different kinds of secretions: a sticky mucus that coats the tongue and traps insects as the woodpecker probes tree crevices, and a more normal spit that helps with swallowing. In flickers, this secretion is very basic, and neutralizes the formic acid coating on ants.
Salivary glands are also very well-developed in swifts and nightjars, whose saliva is fairly thick. The moment a nighthawk opens its mouth for food, rather like the moment I open my mouth at the dentist, glistening saliva is instantly released, so when these insect sweepers fly at rapid speeds into a hard-shelled beetle, their throat is cushioned by the protective spit. Chimney Swifts also take advantage of the thick mucus of their spit to help cement sticks to the inside of a hollow tree or chimney to construct their nest. Some Oriental swifts dispense with the sticks altogether and build their nests from the gelatinous saliva alone. People who eat these birds nests in soup consider it a delicacy, but people who think of it as bird spit soup find it rather unappetizing.
Of all songbirds, the one with the most well-developed salivary glands is the Gray Jay. At bird feeders, we can see whiskey jacks lug off huge chunks of suet, and in campgrounds we watch them carry whole pancakes or pieces of toast. They store this food in caches, even in summer, and apparently the sticky saliva they produce is important in holding wads and chunks of food together. Oddly, their saliva is also used to preserve the food against spoilage. Bird spit is apparently so unappetizing that even bacteria won’t eat it.