OLFACTORY BEHAVIOR OF FORAGING PROCELLARIIFORMS

Olfactory foraging, although very rare among birds, is frequently foun d in members of the Procellariiformes; this finding is based on a smal l number of field studies using a standardized method (i.e. raft tests ). Reactions of seven species previously tested under artificial condi tions were tested again under natural feeding conditions (fish-oil sli cks) to check validity. Concurrently, we compared the flight behavior of two groups of species (with and without olfactory capacities) when approaching an odor source. A large-scale experiment was then conducte d in pelagic waters to test the reaction of a community of procellarii forms (15 species) to a food-related odor diffusing within a principal feeding area. We observed the same reactions (attraction or indiffere nce) to oil slicks as to test rafts in all species evaluated. Results obtained with the standardized method thus hold under natural conditio ns. Species guided by olfaction approached the odor source by flying a gainst the wind very close to (<1 m) the surface, whereas other specie s approached from a direction independent of wind direction and from a greater height (>6 m). Thus, specific searching behavior is associate d with olfactory foraging and we found it to be closely related to dir ection, height, and speed of odor diffusion by wind. Reaction to the o dor test varied according to families or subfamilies, some taxa showin g consistent responses (attraction or indifference) to several experim ents and some taxa showing conflicting reactions. We obtained some evi dence that olfactory behavior may differ before and after locating odo r sources, as well as vary according to oceanic zones (coastal vs. pel agic). We discuss the hypothesis that certain species rely mainly on v isual cues, recognizing and following species that are tracking food-r elated odors. Finally, we propose some new ideas about the evolution o f olfaction in birds.