Grit as an Ecological Factor

Abstract

The pheasant, a highly granivorous species, succeeds best in areas of high calcium concentration. Grains are normally low in calcium content, hence lime-containing grits act as a necessary source of this element. Gravel of the proper chemical composition is particularly significant in the diet of growing birds, and probably for hens during the laying season. Recently glaciated regions where the till possesses high calcium characteristics represent the most suitable pheasant ranges. An example of this is the Minnesota, Dakota and northern Iowa area. The indications are that grit possessing large amounts of magnesium, even though adequate in calcium, is undesirable and may even be deleterious. The first to suggest a possible ecological role for grit was Leopold (1931). In discussing the peculiar distribution of pheasants and Hungarian partridge in the upper midwest, he hypothesized that various dietary factors, which included grit, might be responsible. Data herein reported cover studies relating to the importance of grit in the welfare and distribution of the ringneck pheasant (Phasianus colchicus). Three aspects of the problem are recognized: 1) evidence for any nutritional relationship specific enough to be ecologically significant; 2) problems relative to measuring grit adequacy; and 3) evidence, positive or negative, that grit is important in pheasant ecology under natural conditions. For gallinaceous birds, gravel (as a grinding agent) is generally recognized as an aid to the gizzard. However, any material hard enough to act as an abrasive seems to suffice; therefore, in this role the need for grit seems hardly singular enough to have ecological importance. McCann (1939) has demonstrated that grit is also a source of required nutrient for the pheasant and must be classified under the category of a critical food. By using young, growing pheasants and feeding measured quantities of insoluble gravel (quartz) it was demonstrated that grit consumption quickly rose to extravagant levels with a manifest, frenzied craving for grit, which prevailed over their appetite for normal organic food. This reflected a nutritional need, since feeding with a supplement of bone meal (primarily tri-calcium phosphate) resulted in an almost immediate return to normal grit consumption. In another similar experiment, gravel consisting of glacial 1 Funds for this study were supplied by the National Science Foundation. Facilities were gracioulsly provided by the College of St. Thomas, St. Paul, Minn., and consulting advice was given by the Department of Chemistry, College of St. Thomas. Population data was made available by the Bureau of Game Research, Minnesota Division of Game and Fish.