The problem of how birds find their way can be examined by studying natural migration movements and also by forcing birds to undertake long journeys more or less under conditions which can be decided by the experimenter. The racing pigeon is an ideal subject for these homing experiments, but they have also been conducted with many species of wild bird and Fig. i shows some of the more remarkable flights that have been achieved with these. The use for these experiments of birds breeding in colonies has many advantages as large numbers can be caught and transported together, and their return watched for in a small area. Conspicuous birds such as gulls can be made individually recognizable by a code of plumage marks or by putting coloured leg rings on them.