Weather Forecast


For birds, it's all about the bill

Much can be determined by the structure of a bird's bill. The sharply hooked bill of this Sharp-shinned Hawk indicates its use for ripping into flesh. Keith Corliss1 / 2
Endowed with a huge, chisel-like bill, Pileated Woodpeckers spend much of their lives excavating wood. Keith Corliss2 / 2

An axe-wielding man ambles toward a pile of wood. The obvious assumption is he’s about to create smaller pieces of wood out of the larger ones with the axe. Likewise, when a woman waiting at the doctor’s office pulls a couple of knitting needles out of her purse it’s a safe bet she’s about to continue work on some sort of knitting project. The tool says it all.

It’s the tool sticking out the front of a bird’s head that declares what the bird is and what it’s designed to do. This amazing bone-and-keratin structure called a bill (or sometimes, beak) veritably defines what the life of a particular bird will be.

Take a fairly heavy bill with a hooked end. Well, that one is destined for the life of a flesh-ripper, like those found on eagles, falcons, hawks, and owls. If the bill is thick and conical like those of sparrows and finches, seed-cracking will occupy its feeding hours. Warblers and wrens, with slender pointed bills, are equipped with a tool specific to plucking insects out of various hiding places in their environments.

In this way, each species has evolved a specific bill shape and size to accommodate and facilitate a niche-based life—diverging from each other over time. Charles Darwin’s trip to the Galapagos Islands in 1835 aboard the HMS Beagle, produced dramatic evidence among the finches found there. And where did he find it? In the birds’ beaks. He wrote, “It is very remarkable that a nearly perfect gradation of structure in this one group can be traced in the form of the beak, from one exceeding in dimensions that of the largest grosbeak, to another differing but little from that of a warbler.”

From a single ancestor arose 13 related but distinct species of finch—the very definition of adaptive radiation—each with a different bill and thus a different feeding style. Some are ground-dwelling seed-eaters, some are cactus-seed eaters, and seven are arboreal insect eaters. Regardless, it’s the beaks, the tools, which make them unique.

When I first started birding years ago, someone told me to pay particular attention to a bird’s bill, that it would tell you more than any other piece of evidence what species a bird was, or at least its family. It’s true.

Just how important is this bill thing to a bird? It’s not only its hand-and-mouth; it’s everything, a built-in Leatherman tool.

This instrument is used for preening, reaching nearly all of a bird’s body. It collects nesting material when it comes time to build the nursery. It’s a weapon, used both offensively and defensively. On the part of woodpeckers, it’s a necessary chisel, creating cavities in which to build nests. Oystercatchers use their bills as a pry bar, breaking shellfish open along both coasts to reach the meaty morsels inside.

There is so much diversity, so many different modifications in the beaks of birds; one cannot even begin to explain it all. Ducks, geese, and swans, for instance, have soft flattened bills but all have a hardened structure at the tip (often bent) called a nail, used primarily in food-gathering.

The softest bills reportedly belong to the snipes and woodcocks. Both sport very long thin bills filled with vascular tissue and sensory receptors. Used to probe into damp earth beneath leaf litter, the tactile ability of their bills allows the birds to locate and eat their preferred food—earthworms.

The range of bill shapes and sizes among the world’s bird species is exceedingly vast, from thin, nectar-sucking bills of hummingbirds to huge horny bills such as those found on pelicans; from the beefy spear of the Belted Kingfishers to the long, delicate, upturned one of the elegant American Avocet.

Each species’ bill is unique in some way, optimally serving the needs of its owner. Pay particular attention to the detail and structure of a bird’s bill next time you get a chance and watch how it’s used. You’ll find it’s more than just a mouth-like part to the bird, it’s their all-everything tool; their digger, their scratcher, their purse, their excavator, their weapon, their smeller. It not only provides for the bird, it is its very identity.