Swimming with Piranhas at Feeding Time by Richard Conniff

Author:Richard Conniff
Language: eng
Format: epub
Publisher: W. W. Norton & Company
Published: 2009-08-14T16:00:00+00:00

Wicking and Licking

The ancestors of hummingbirds probably started out feeding on tiny insects around flowers, and only incidentally got their noses into the nectar. But they took to flower-feeding like a small child to lollipops. Hummingbirds and certain flowers have subsequently adapted in all kinds of weird ways for the blissful moment or two when they come together. In the Andes, for instance, certain passionflowers have developed an elongated tubelike shape. Local hummingbirds in turn have evolved 4-inch-long swordbills for reaching deep down to the nectar at the bottom of the tube. When they finish feeding, the hummingbirds inadvertently carry a dusting of pollen on their bills and heads and deliver it to fertilize other passionflowers, sometimes miles away. The birds are the flowers’ primary pollinators.

Hummingbirds have also evolved incredibly long, specialized tongues. If you hold a hummingbird in your hand and offer it a feeder, you can sometimes see the white flickering of the tongue entering the feeder hole just ahead of the bill. If you blow gently on the bird’s head feathers as it feeds, you can actually see the tongue muscles pulsing under the translucent flesh at the back of the skull.

This may seem anatomically unorthodox. The tongue itself fills the hummingbird’s bill, so the muscles that support the tongue actually run back around the spinal cord, up the outside of the skull and over the top, to be anchored between the eyes. In some species, the tongue is fringed along the outer edge, which may help entangle insects. In some, the tongue ends in two troughs with which the bird draws up nectar—not by sucking but by capillary action—as the tongue flicks in and out. While the human spectators are whooping and dooping, the hummingbirds, in Calder’s words, are wicking and licking.

So far, this is pretty straightforward. But as the relationship between flowers and hummingbirds evolved, certain mites figured out how to get in on the party. These tiny relatives of ticks and spiders eat nectar and pollen, and each mite species has evolved to feed on particular species of flowers. Getting from one flower to another can be a problem—especially given that mites are blind and may specialize on a bromeliad 100 feet up a tree in the middle of a rain forest. So the mites have evolved to use hummingbirds as their C-47s.

Sooner or later a hummingbird will show up to feed on the flower a mite has been busy plundering. Then, according to University of Connecticut biologist Robert Colwell, the mite sprints up the hummingbird’s bill and hides in its nasal cavity. The hummingbird doesn’t seem to notice the stowaway. Colwell has found as many as 10 or 15 mites per bird, and because a hummingbird typically feeds on many different flower types, the mites have at times belonged to as many as five species.

The mites are only along for the ride to the next preferred flower. Colwell describes them as “perpetual airline passengers that carry out all their mating and feeding in airport lounges.

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