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Master Naturalists: A bird beak for every meal

By By Paul and Mary Meredith
Nov. 7, 2013 at 5:07 a.m.


Herons and cranes hunt while wading or moving in marshy areas. Their feeding habits differ. Cranes are "stand still and stab" hunters, waiting to capture prey by stealth using their long, narrow bills to catch prey (frogs, fish, crabs, and bugs) as the prey move about unaware. On land, they pluck fruit such as wolfberries and other seasonal fruits and vegetables. Herons' heads and bills are heavier (that's why they fly with their necks bent) for wade-hunting prey to grab or snatch. They even dig tubers and rhizomes with their shorter, heavier bills.

It's easy to tell that birds' beaks have adapted so they can efficiently catch and hold their normal food. Ducks have wide, flat beaks to find plants and small, aquatic creatures in muddy rivers and pond bottoms. Pelicans have large bills to dive on or scoop fish.

Wading spoonbill bills are paddle-shaped and touch-sensitive - perfect for gleaning food like small fish, shrimp, mollusks, snails and insects as they swing their open bills from side to side. Raptors, as carnivores, all have heavy, hooked bills with sharp, cutting edges to catch, kill and tear apart prey.

Hummingbird bills - how have they adapted?

Hummers, unique to the Americas, adapted - with long, thin, light beaks and special tongues that curl up into their skulls, giving them access to nectar in long, narrow flowers. Some have curved beaks, adapted to feeding on and pollinating specific plants with curved flowers.

Heliconias (bird of paradise plants) in the Caribbean are only pollinated by a specific group of curve-billed hummers called "hermits," whose bills perfectly match the flowers' throats. Yes, hummers drink nectar for energy. But 40 to 60 percent of their diet is insects and spiders.

We regularly see our hummers browsing rose and milkweed plants - not for nectar but for aphids. They also eat small bugs and spiders on flowers as they search for nectar. What is startling is that they eat mosquitos, flies and even gnats, catching them on the fly.

A bill for catching flying insects?

If you designed a hummer bill to catch flying insects, it would look like a swallow's, a flycatcher's or even a mockingbird's - short and pretty wide. Could you catch a gnat with pair of tweezers? I'd rather have a rolled paper or flyswatter. So how do hummers catch little insects on the fly with a tweezer-like bill?

Biologists taking high-speed movies of three hummer species feeding on small flies were surprised to find two striking adaptations. First, hummers, including Ruby throats, can open their lower beaks really wide, up to 20 degrees, effectively making their mouth much bigger to better scoop up an insect. That big opening is certainly not needed for nectar extraction or for plucking nonflying prey.

Then, they were really startled by the hummers' second adaptation. Their films showed hummers can also flex their lower jaw laterally (just like we can) to widen the area at the base of the beak, again giving an effectively bigger mouth for catching prey.

As Dr. Margaret Rubega, evolutionary biologist and ecologist at University of Connecticut, commented, "If anyone had said hummingbirds' beaks are bending before we saw the video, we would have said that's crazy." So hummers turn out to be efficient flying-insect feeders after all.

Sources:

Hummingbird's Beaks Bend To Catch Insects, Researchers Say, By Elizabeth Omara-Otunnu, http://advance.uconn.edu/2004/040719/04071910.htm

The Virtual Rainforest: Hummingbirds and Heliconias, http://www.globalchange.msu.edu/rainforest/Content/Crowned-Woodnymph-Hummingbird.html

Paul and Mary Meredith are master naturalists. Contact them at paulmary0211@sbcglobal.net.

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