Simulated navigation based on observed gradients of atmospheric trace gases (models on pigeon homing, part 3)

An earlier developed model, simulating pigeon homing based on fictitious gr adients of atmospheric odours, was applied to actually observed spatial dis tributions of volatile hydrocarbons. The model calculations demonstrate tha t sufficient information on a bird's current position with respect to home can be derived from the ratios among three or more chemical compounds which gradually vary over distances of several hundreds of kilometres, different ly in different directions. might directions computed by model birds from s uch observed ratios are roughly but not perfectly homeward-oriented from mo st positions within the investigated radius of 200 km around home. Performa nces of model birds are at least as good as those of real pigeons in the fi eld. According to calculations using atmospheric data collected under diffe rent wind directions, the birds might, but possibly need not, take the curr ent weather conditions into account when evaluating olfactory signals. It i s necessary, however, that the birds acquire, during their long-term stay a t the home site, some knowledge of the directions of relevant gradients. Ho ming experiments with pigeons as well as measurements of atmospheric trace substances are consistent with the hypothesis that this knowledge is gained by correlating wind directions with specific changes of ratios among a num ber of compounds. This assumed process requires further elucidation. (C) 20 00 Academic Press.