A tropical bird with an unusual digestive system can process plant fiber just as efficiently as a cow, an ornithologist has found.
The scientist, Dr. Alejandro Grajal of the Wildlife Conservation Society, and his colleagues reported six years ago that the species, the hoat-zin, was the only bird known to have a digestive system similar to a cow's. The hoatzin, also known as the stinkbird, has an enlarged crop and esophagus where bacteria break down the cellulose in plant cells into sugars that the bird can digest.To continue his research, Grajal captured nine hoatzins along the Guarico River in Venezuela and fed them diets of romaine lettuce, ground alfalfa and hay pellets, ground timothy grass and ground roasted soybeans.
"The surprising result is these animals have an incredible efficiency in digesting fiber, higher than anything measured in birds," he said. The hoatzins digested up to 70 percent of the plant fiber, he found in the study, published in the current issue of the journal Ibis.
The bird's digestive system, known as foregut fermentation, is similar to that found in cows, Colobine monkeys, kangaroos and tree sloths. Only 3 percent of bird species feed extensively on green leaves or buds, and most birds in the tropical jungle eat insects or fruit.
One advantage of the hoatzin's culinary preference is obvious: it is everywhere surrounded by an abun-dant food source, the plants of the tropical jungle. Another possible explanation for the bird's unusual digestive tract is that the bacteria may destroy toxins found in the plants, conferring an evolutionary advantage.