Richardson 1937 Barley Camp, Warner Mts., 14 mi. SW Adel, Lake C., Oregon June 4, 1937. The lack of certain species in a given region may serve as a clue to what conditions are optimum, but may be puzzling when conditions seem right for them, especially when the region corresponds to one in which the species are already known. When this latter seems true we are forced to conclude (speaking here primarily of resident birds) that the species has not reached a balance i.e. does not occupy all of its biotopes available, or that it is not completely resident but must wander, perhaps depending on the food supply. A related question is why do not some species increase far beyond normal, so when the food available to them seems unlimited? Partial answer to this is that we are liable to notice an abundance of food and not its scarcity. Thus great swarms of insects as Mayflies may be seen but may be absent other years. The presence or abundance of a species is certainly influenced by many factors, apparently working to the best advantage of the species over the years of its evolution - years involving extreme of condition