OLFACTORY EXPERIMENTS ON CORY SHEARWATER (CALONECTRIS-DIOMEDEA) - THE EFFECT OF INTRANASAL ZINC-SULFATE TREATMENT ON SHORT-RANGE HOMING BEHAVIOR

Experiments were carried out with anosmic Cory's shearwaters to verify whether these birds, which are strictly nocturnal in their activity on land, use olfactory cues to localize individual nest burrows. Both the experimental birds, subjected to intranasal injection of zinc sulphate solution, which produces a reversible impairment of the olfactory mucosae, and unmanipulated controls were captured at their breeding colony on the island of Linosa (Pelagian Islands, Italy). Releases were carried out on the coast nearly 2 km away from the breeding colony. Recoveries at the nests showed that experimentals achieved significantly poorer homing success than controls. The view that the birds were disturbed in a non-specific way by experimental manipulation is weakened by the fact that injection of the same zinc sulphate solution into the coanae, a method only marginally involving the olfactory receptors, does not influence homing behaviour. Our results indicate that in Cory's shearwaters the search for individual burrows is based on, or at least complemented by, olfactory cues.