Effects of calcium-loading on egg production in ring-necked pheasants

Ring-necked pheasants (Phasianus colchicus) are able to store dietary calcium as medullary bone, which they may mobilize for future eggshell synthesis. We define this mechanism as calcium-loading. Previous experiments on pheasants conducted to document the importance of calcium in limiting distribution did not account for calcium-loading. We hypothesized that calcium-loading could override experimental calcium treatments of the diet. We measured egg production, egg characteristics, and femoral mineral content for pheasants that were not calcium-loaded on 7 diets differing in calcium from 0.2 to 4.5 and compared these results to a similar study on calcium-loaded pheasants. We predicted that calcium-loaded pheasants would produce more eggs than those that were not calcium-loaded. We also predicted that there would be no significant difference between femur ash fractions in noncalcium-loaded pheasants, but that the ash fraction in calcium-loaded pheasants would differ significantly between the beginning and end of the experiment. Egg production was higher in calcium-loaded pheasants above 2 dietary calcium. Femur ash fraction was not different in noncalcium-loaded pheasants but differed significantly before and after the experiment and between high (>2) and low (<2) dietary levels in calcium-loaded pheasants. Calcium-loading may account for short-term persistence of captive pheasants introduced on calcium-poor soils, followed by their eventual population failure. Managers may improve survival of captive pheasants before introduction by surveying habitat for adequate calcium and by calcium-loading.