Green Blog: Droopy Flowers and Their Wiles

Some flowers ply the art of seduction, dressing in showy colors, flouncing their petal skirts and grinning up at the sun, seemingly enthralled by their own attractiveness. But what about the ones that droop? Can they attract enough pollinators to thrive in a garden filled with extroverts?

A study published in the British journal Functional Ecology shows that rather than being at a disadvantage, such flowers are masterminds at managing pollinators to their benefit. And that?s where the hummingbird comes in.

The gleaming creature with a long sickle-like beak is often associated with bright tubular flowers. But Nir Sapir, an avian ecologist who works with the Max Planck Institute of Ornithology and a co-author of the paper, said that ornithologists have long been aware that hummingbirds feed from flowers that of varying shapes and colors, often those that are oriented downward. Dr. Sapir and his co-author and postdoctoral adviser, Robert Dudley, who specializes in animals? flight mechanics, set out to examine the relationship between the hummingbird and the drooping bloom.

For their muse, they chose the Anna?s hummingbird, a species with iridescent olive-green feathers (and, in the male?s case, a magenta ruff) that is common on the campus of University of California, Berkeley, where their research took place. After catching the birds, Dr. Dudley and Dr. Sapir placed them in an airy Plexiglas cube that was large enough to allow flight and contained artificial flowers into which nectar-filled syringes had been inserted. The flowers were oriented to point either horizontally, at a 45 degree downward angle or directly facing the floor.

Some of the flowers had a mesh-like mask that measured the bird?s uptake of oxygen as it closed in on a bloom. The researchers anticipated that this would demonstrate that hummingbirds breathe more slowly and use up less energy when supping nectar from lower-hanging flowers, which could explain the attraction to blooms oriented this way.

Instead, they discovered the opposite. Energy-wise, ?it doesn?t pay off for the hummingbirds to feed from these flowers,? Dr. Sapir said. Using the oxygen measures and a high-speed camera to record in-flight motion, the researchers noticed that the drooping flowers required the birds to feed by pulling their bodies upright and jerking back their heads, which requires more energy than feeding from flowers that don?t droop.

Why, then, do the birds bother visiting the flowers at all? ?I think the answer is a bit complicated and largely unknown,? Dr. Sapir said ? but he offers a possible explanation.

A flower that droops shields its nectar under its petals, thereby protecting it from the diluting effects of rain. A visiting bird can then reap the unadulterated liquid, which could explain the extra effort it expends. Besides, given that few other birds can feed at such odd angles, the hummingbird customarily gets first dibs on the prize.

By hanging, the flower caters to the hummingbird?s unusual skills ? something the plant may have evolved to do because of the bird?s reliable pollinating habits. ?I think that the hummingbird may be an efficient pollinator because it has a good memory,? Dr. Sapir said. The birds remember what flowers they have frequented and move along to others accordingly. That way, they spread flower pollen more widely than they would if they didn?t have an internal memory map.

Nectar also happens to be an energy-intensive commodity to produce, Dr. Sapir said. Hence a flower does not benefit if every pollinator in the neighborhood stops by to swig its nectar.

Essentially, the flower ?creates ways to select or control the identities of its pollinators,? he said. The hummingbird?s niche is being strong and capable enough to feed at difficult angles, and the bloom benefits because the bird casts pollen so widely.

Source: http://green.blogs.nytimes.com/2012/11/21/droopy-flowers-and-their-wiles/?partner=rss&emc=rss

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