OLFACTORY BEHAVIOR OF FORAGING PROCELLARIIFORMS

Olfactory foraging, although very rare among birds, is frequently found in members of the Procellariiformes; this finding is based on a small number of field studies using a standardized method (i.e. raft tests). Reactions of seven species previously tested under artificial conditions were tested again under natural feeding conditions (fish-oil slicks) 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 conducted in pelagic waters to test the reaction of a community of procellariiforms (15 species) to a food-related odor diffusing within a principal feeding area. We observed the same reactions (attraction or indifference) to oil slicks as to test rafts in all species evaluated. Results obtained with the standardized method thus hold under natural conditions. Species guided by olfaction approached the odor source by flying against the wind very close to (<1 m) the surface, whereas other species approached from a direction independent of wind direction and from a greater height (>6 m). Thus, specific searching behavior is associated with olfactory foraging and we found it to be closely related to direction, height, and speed of odor diffusion by wind. Reaction to the odor test varied according to families or subfamilies, some taxa showing consistent responses (attraction or indifference) to several experiments and some taxa showing conflicting reactions. We obtained some evidence that olfactory behavior may differ before and after locating odor sources, as well as vary according to oceanic zones (coastal vs. pelagic). We discuss the hypothesis that certain species rely mainly on visual cues, recognizing and following species that are tracking food-related odors. Finally, we propose some new ideas about the evolution of olfaction in birds.