Certain seabirds drawn by the smell of food.

Some inconspicuous seabirds, such as prions and white-chinned petrels, behave like the bloodhounds of the Antarctic skies, a new study suggests.

These birds apparently use their sense of smell to track down food in the vast expanse of the South Atlantic Ocean, Gabrielle A. Nevitt of the University of California, Davis, and her colleagues assert in the Aug. 24 Nature. The birds may locate zooplankton, tiny ocean animals that they feed on, by following the odor of dimethyl sulfide (DMS), which gets released when zooplankton graze on phytoplankton (single-celled plants). The team estimates that these birds can detect normal ambient concentrations of DMS from up to 4 kilometers away.

Ornithologists have only recently accepted the idea that birds can smell at all, and most researchers who study their foraging techniques ignore the significance of odors, contends Bernice M. Wenzel, of the University of California, Los Angeles, School of Medicine.

DMS has also piqued the interest of climatologists, who are debating whether the compound could increase the concentration of cloud-forming particles in the atmosphere and alter temperatures (SN: 12/10/88, p. 375).

From their ship, Nevitt and her colleagues sprayed both a DMS-scented and an unscented aerosol plume into the air. They also poured out cod-liver oil  and unscented and DMS-scented vegetable oil, which formed slicks on the water. Concentrations of DMS resembled what the birds might naturally encounter.

On average, twice as many birds came to the DMS-scented slicks as the unscented oil, and they found the scent as enticing as cod-liver oil. The birds zigzagged over the DMS slick, sat on it, tasted it, or just hovered over it. Although white-chinned petrels, prions, and two species of storm petrels found the DMS compelling, albatrosses and cape petrels showed no particular interest in it. The researchers obtained similar responses with the plumes.

All of the studied birds belong to the order Procellariiformes, and have unusually large areas in their brains responsible for smell.

The authors speculate that species showing no preference for DMS may have detected the odor but not considered it a food cue. Such birds may instead rely more on visual cues--finding food by watching where others head. Unlike the DMS-sensitive birds, the nonresponders are quite visible, forage mostly by day, and join large feeding groups, Nevitt observes.

The scientists are investigating whether blacked-brow albatrosses space themselves differently than do the DMS-sensitive birds in order to watch each other. "We're just wondering whether they hunt differently," Nevitt says.

Other studies have shown that birds will follow odors, such as ground-up squid and fish oil. But "it's rare to see such a pronounced response to such a pure aromatic [as DMS]," Nevitt says.

Indeed, the strength of this study stems from its use of a natural odorant, agrees Jerry A. Waldvogel of Clemson (S.C.) University.