Why are camels' red blood cells nucleated?

Camels have nucleated red blood cells because the cells help continue blood flow during times when water is scarce. The blood cells can significantly expand during rehydration. They are capable of expanding up to 240 percent of their original volume. Normal red blood cells can only expand 150 percent.

The camel can go days without drinking water. During this time, it can lose up to 40 percent of its body weight in water. The long axis of the oval blood cells permits them to move easily with the flow of the blood, ensuring that the blood can reach the camel's smallest blood vessels.