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The Scent of a Carcass

When some scavengers follow their nose to their next meal, it's not the complexities of the carrion scent that draws them, but the simple lure of a good strong whiff. Field experiments indicate that mud snails flock to injured animals and carcasses based on how fast chemicals oozing from the prey bombard the snails' sniffing organs. The finding, reported in the June issue of the journal Ecology, suggests that for these snails, getting a quick snootful may be more important than a discerning palette for finding food.

Scientists have assumed that organisms respond to scents based on the concentration of various chemicals. To find out whether the behavior of animals in the wild depends more on the chemistry of odors or the physics of how they spread, Richard Zimmer, a chemical ecologist at the University of California, Los Angeles, and several colleagues set up a test in an aquatic environment.

The team observed how mud snails reacted to fresh chunks of meat placed in a tidal creek. By varying the type of bait, the team found that no matter what blend of amino acids leaked away, roughly the same number of snails flocked to the bait so long as the intensity of the odor was constant. "We could change the composition of the mixture from essence of crab to essence of clam, and the snails could have cared less," Zimmer says. Rather, the critical factor was the strength of the odor--determined by the concentration of amino acids in the body fluids and the rate they moved down the creek.

The study is an elegant demonstration of the importance of odor transport, says Gabrielle Nevitt, a sensory ecologist at the University of California, Davis. That's an impressive accomplishment, she adds, noting the difficulty of precisely measuring scent transport in the wild.