As Gause's hypothesis suggests on theoretical grounds, differences can be shown to exist in the habitat, feeding niche, and in the nature and she of food taken by the British finches. Under experimental conditions, changes occur in the adult's seed choice which tend to increase the proportion of large seeds in the diet. DSerenoe-9 in the extent and rapidity of these changes exist between the spies, those with large bills changing more quickly than others. Differences can also be found in feeding techniques. Development of seed husking technique WBB studied in the chaffinches and followed early mandibulation of the feathers. Experiments showed differences in the time taken by adult chaffinches to husk various seeds, and in amount of kernel obtained from each for the same husking effort. Comparisons were made by timing seed-husking in other species. Large-billed species husked the large seeds quickly and more efficiently than the small-billed birds. It is suggested that demonstrated differences between the speaie-9 in seed selection depend largely on differences in bill structure that condition learning in the individual. Other factors effecting food selection are age, seasonal change, diet restriction and social experience.