Let's Talk About Birds: Hornbills


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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.

 

What do toucans and hornbills have in common? What sounds like the beginning of a bird joke is actually an interesting comparison to make as we talk about one of the National Aviary's most popular species, the rhinoceros hornbill.

Like the more familiar toucans, hornbills have extremely large (but surprisingly lightweight), often colorful bills. Both use their bills to feed mostly on fruits but also insects, bird's eggs and small animals. Both also nest in holes in trees (although with one important difference). Despite having these things in common, toucans and hornbills are not closely related at all; their outward similarity is a result of evolutionary convergence to a similar lifestyle. More than 50 species of hornbills are found throughout Southeast Asia and Africa, while toucans of more than 40 varieties are found in Central and South America.

Toucans and hornbills are also similar in the drastic size differences that exist among their species, with the smallest species in each being the size of a backyard songbird, the largest as big as a hawk or eagle. For example, the rhinoceros hornbill is among the world's largest hornbills -- 4 feet long and more than 6 pounds. The black dwarf hornbill is only a foot long and weighs less than a quarter of a pound -- not much bigger than a blue jay.

Hornbills have evolved one of the most unusual breeding strategies of any bird, and this is where they differ greatly from toucans. After mating, the female hornbill seals herself inside a tree cavity using mud, fruit pulp and other soft materials that form into a hard plaster when they dry. Once sealed inside, she remains there for the time it takes to lay two to six eggs, incubate them for several weeks until they hatch, and raise the nestlings until they are at least half-grown. In the case of the rhinoceros hornbill, this translates into self-imposed captivity of 21/2 months.

During all this time, the only food that she and her nestlings get is what her mate brings and passes through a small opening to the nest cavity just big enough for the tip of his bill. The female hornbill uses her "stay-at-home-mom" time wisely -- while sequestered in the nest cavity, she molts a whole new set of feathers, something toucans can't do.

The rhinoceros hornbill pair at the National Aviary has a spacious new habitat in the newly opened "Canary's Call" exhibit, and they're busily making themselves at home. One day soon, we hope, visitors to the National Aviary will get a firsthand look at their unique nesting behavior.


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