Supplemental feeding of birds is usually only cone for songbirds but does occur with waterfowl species and turkeys under certain circumstances. The feeding of waterfowl during the winter may encourage alterations of normal migration patterns and possibly be of disease importance. Avian species respond faster to the providing of food once physical condition has been affected. Consequently, if the necessity arises, supplemental feeding can be started at anytime and probably be successful. Deaths attributable to starvation may have a great and persistent effect on a population, not only due to the loss of individuals, but also due to the disruption of fertility and reproductive success.
Pregnant females catabolize their own fat and protein reserves during periods of food deprivation.
The fetus is protected by these actions and continues its development. If a pregnant female is forced to withstand prolonged malnutrition, however, the fetus may die and be resorbed or aborted. A fetus that is not resorbed or aborted, but survives and continues its development to term, may be born small and have a reduced chance of surviving. This is especially true if malnutrition occurs during the third trimester of the pregnancy. These small offspring will probably have difficulty in suckling and the female may not permit them to do so, thus rejecting them.