The bird lays eggs that have a protective shell. Sometimes the male helps the female warm the eggs. Baby birds require care and therefore the birds build nests for them to live and hatch in. Excretion A bird has skin covered with feathers. They lose their feathers or molt once a year.
New feathers grow back to replace the old ones.
The bird has kidneys and a ureter to excrete liquid wastes and intestines and a rectum for solid wastes. Symmetry A bird has bilateral symmetry. Appearance A bird ranges in size from around two inches to seven feet. Birds can be many colors. Frequently the male is more colorful and the female is drab.