Some years ago now, excellent birder and bird photographer Richard Ditch and WC co-authored a couple of articles on bird identification for bird photographers. Richard did most of the work, and made an excellent point: a bird’s bill is a good starting point for identifying the bird’s species and figuring out how the bird makes a living. With that credit to Rich, WC will undertake to give some examples of the astonishing evolutionary adaptations of birds’ bills to birds’ business.
This time WC will briefly explore a few species whose bills are, in effect, fishing spears. Like the bills of raptors, there is a general design and then variations among the species.
The classic shape of a bill used for spearfishing is probably the Great Blue Heron’s.
Sharp, long and stout, it’s a generalist tool. While Great Blues eat mostly fish, they also eat small mammals, reptiles, amphibians and even other birds.
In contrast to the generalist spear of the Great Blue, the American Bittern has a needle sharp bill and dines almost exclusively on fish, which it stabs, rather than grabbing.
The Green Heron’s bill is somewhere between the generalist Great Blue’s and the specialist Bittern’s. Unsurprisingly, the Green Heron’s diet is more general, and includes a lot of invertebrates.
The Reddish Egret is another fish specialist. It’s technique is different, though. Most of these spearfishing birds ambush their prey, waiting frozen for prey to come near. The Reddish Egret tries to startle its prey into movement and then strikes. It has a variety of wing-flicking and running techniques, all intended to spook prey into movement, at which it strikes.
When a bill is curved, even slightly curved like a Limpkin’s, it means the bird is likely not a spear fisher. In fact, if you look closely you can see the Limpkin’s bill curves slight to the right at the tip. That makes it useless for spearing fish, but ideal for extracting Apple Snails from their shells. (It says something about the abundance of Apple Snails that the prey supports both Limpkins and Snail Kites.) The Limpkin illustrates the importance of very close examination of a bird’s bill.
No discussion of North American spear-fishing birds would be complete without the Anhinga.
Unlike the other birds, all of which are waders, the Anhinga, the Snakebird, is a swimmer and diver. It gets its nickname because when it swims its body is usually submerged, with only its head and neck above the water. Unlike most aquatic birds, Anhingas have fully wettable plumage and dense bones, adaptations that allow them to achieve neutral buoyancy in water, enabling a slow, stalking hunting style. The Anhinga shakes captured prey vigorously, and then tosses it in the air, catching and swallowing it headfirst.
There are many, many other spearfishing bird species. WC will revisit some of them later. But this sampler shows how diversified and specialized even one kind of bill can be. And why WC finds birds endlessly fascinating.