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 gradients of atmospheric odours, was applied to actually observed spatial distributions of volatile hydrocarbons. The model calculations demonstrate that 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, differently in different directions. Flight directions computed by model birds from such observed ratios are roughly but not perfectly homeward-oriented from most positions within the investigated radius of 200 km around home. Performances of model birds are at least as good as those of real pigeons in the field. According to calculations using atmospheric data collected under different wind directions, the birds might, but possibly need not, take the current weather conditions into account when evaluating olfactory signals. It is necessary, however, that the birds acquire, during their long-term stay at the home site, some knowledge of the directions of relevant gradients. Homing 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 number of compounds. This assumed process requires further elucidation.