Let's Talk About Birds: Boat-billed heron

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This is one of a series presented by the National Aviary, which works to inspire respect for nature through an appreciation of birds.

The boat-billed heron doesn't exactly fit the heron mold. When you think of a "heron" you probably envision a tall, long-legged, grayish bird with an S-shaped neck and a long pointed bill. Indeed, that is the classic heron form, and it describes a species that most of us know very well, the great blue heron. Worldwide there are more than 60 species in the heron family, Ardeidae, which also includes the bitterns and egrets. Most of these -- from the tiny 12-inch-tall least bittern to the gigantic 5-foot-tall goliath heron -- really are cookie-cutter versions of one another, differing primarily in size and color.

But there are two things that are distinctive about the boat-bill: It has exceptionally big eyes and a very wide, keel-shaped bill. Both of these features reflect differences in the behavioral ecology of this species compared to other herons. Its large eyes are a clue that the boat-bill feeds mostly in low light conditions. In fact, it is both crepuscular (twilight active) and nocturnal. During the day it spends most of its time perched, resting or preening. At dusk and at night it forages in the murky shallows of mangrove swamps and lagoons, which are its natural habitat from Mexico south through Central America into parts of South America.

Its uniquely shaped bill probably is an adaptation for feeding on small crustaceans and other prey that live in the muddy waters of sluggish tropical streams and rivers. Some observers have reported that in addition to stabbing at prey that it sees, as other herons do, it uses its broad bill like a scoop to sift through muddy substrates and strain out shrimps and other hidden prey.

Some ornithologists instead believe it serves a communication function in social interactions.

The truth is that we really don't yet know the functional morphology (how it works in an engineering sense) or adaptive significance (why it is advantageous in an evolutionary sense) of the unusual bill that gives the boat-billed heron its name -- it is an interesting question for a future graduate student in biology to answer.

You can observe a colony of boat-bills at the National Aviary, and an upcoming program will give visitors special access to this unusual species. Our popular "Photo Safari" series begins Saturday. Registered participants will be able to photograph the birds of the Wetlands exhibit for an hour before the National Aviary opens to the public, and trainers will be on hand to lure birds closer for some rare photo opportunities.

Details at www.aviary.org.

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