Rails Cranes and Relatives: Gruiformes - Physical Characteristics
Gruiforms, birds of the order Gruiformes, vary greatly in size. The smallest species, the American black rail, is only 4.7 inches (12 centimeters) high, whereas the Sarus crane, at 5.8 feet (176 centimeters), is the tallest flying bird. Weights in the group also vary tremendously. The American black rail weighs in at only 8 ounces (20 grams), while kori bustards and great bustards have been known to reach weights of more than 40 pounds (18 kilograms), making them among the heaviest flying birds.
Most species of Gruiformes are primarily black, gray, or brown in color, and many species have streaked markings. However, there are some exceptions, including the sunbittern and some rails and cranes. Rails are sometimes greenish or purplish in color. Cranes have black or white feathers, often with distinctive patches of red skin on the head and neck. The sunbittern is a particularly colorful gruiform, with large black and red "eyespots" on its wings—these spots resemble the eyes of a much larger animal and help scare off potential predators.
Bill shape also varies among the gruiforms. Cranes have narrow, medium-length bills that they use to search for invertebrates in soft mud. Trumpeters, which search for food on rainforest floors, have short bills resembling those of chickens. The limpkin has an extremely unusual bill, which bends to the right at its tip. The limpkin's bill is adapted to feeding on apple snails, its primary food.