The Rainforest Canopy
BIRDS OF THE RAINFOREST CANOPY
July 30, 2012Of the more than 10,000 species of birds in the world, the majority are found in the tropics with 50 percent of all bird species found in the Amazon Basin and Indonesia.
PARROTS
One of the most recognizable bird groups in the world is the parrots (about 315 species) with their bright colors, distinctive loud calls, powerful beaks, and feet with two toes facing forward and two facing rearward. Parrots are most prominent in the rainforest, although they are found in countless other tropical habitats around the world. Parrots feed on seeds, fruits, grass, leaves, and plant shoots and use their strong beaks to crack hard shells, grind their food, and as a third limb for climbing. Parrots come in a range of sizes from the 39-inch (1 m), three-pound (1.4 kg) hyacinthine macaw of Brazil to the pygmy parrot which rarely reaches three and a half inches (9 cm) and weighs only about half an ounce (15 g). Besides size variation, some parrots have very unusual habits, like the Southeast Asian hanging parrots which sleep hanging upside down like bats. Many parrots live in flocks or in life-long partnerships with a single mate. When one member of the pair dies, the other mate either lives out its life in lonely solitude or joins another pair to make a triple. Many parrots show marked sexual dimorphism with males usually more strikingly colored than females. Due to their attractive coloration, many parrots are threatened by over-collecting for the pet trade in addition to threats from loss of habitat.
Each continental region has its own form of giant parrots: Central and South America have macaws, while Australia and Southeast Asia have cockatoos. Macaws are well known throughout the New World for their bright colors, their loud call, and their demeanor as pet birds. In addition, macaws are famous for gathering by the hundreds, even thousands, along the clay cliffs of the Amazon river where they feed on minerals which bind to the seed toxins, rendering the seeds on which they feed less toxic by preventing their absorption. The world's rarest bird is a macaw, Spix's macaw, which is a beautiful bird with a dark blue head, a blue body, and a greenish belly with a black mask and bright yellow eye. It has always been rare, limited to palm groves and river edges in small areas near the center of Brazil, but recent deforestation, importation of Africanized bees—which took their tree hollows—and over collection for hobbyists caused this species' demise. In 1987, four birds remained; now only a single male bird may remain as the species' lone wild representative on Earth. Cockatoos are also widely kept as pets for their attractive plumage and well-developed crests, but are routinely killed in their native lands as menaces to crops.
WORLDWIDE CANOPY BIRDS
Swifts are interesting birds found worldwide, though generally not considered rainforest birds since they may spend 2-3 years in flight, before landing to nest in caves, emergent canopy trees, or buildings. Swifts can only land in locations with altitude because their wing structure,built for extended flight,does not facilitate conventional take-off. Swifts are able stay aloft for such extended periods because of their two-lobed brain which allows for one half to "sleep" while the other performs bodily functions like flying and catching insects in flight. Swifts are well-known in Asia not for their stamina, but for their nests built of their saliva and blood, mixed with twigs. These nests are constructed in large numbers in caves in Southeast Asia and in tall forest trees in Africa. The nests are built upside down and the eggs are glued in with saliva. The nests are popular as a delicacy believed to bring good luck.
Owls are successful nocturnal birds of prey that are found worldwide. They are successful due to their superb adaptations to nocturnal hunting. Despite their immobile eye sockets, owls have incredible vision. Their cornea is highly convex so that their vision up, down, left and right is good, and they have the ability to turn their head up to 270 degrees. The face of an owl is disk-shaped in order to pick up more light and sound waves, much like a satellite dish. The owl's hearing is far superior to that of a human thanks to the placement of the ears: the right ear is located above the left ear and pointed at a different angle so the owl can perceive vertical sound movement in addition to the horizontal sound movement that humans can detect. In addition to sight and hearing, the owl has physiological adaptations to make it nearly silent when it flies. The chest and underwings are soft down feathers and the owl flies with a butterfly-stroke motion to ensure stealth.
Rainforests are home to many other birds of prey like hawks, eagles, and vultures. Vultures are seen virtually everywhere in the tropics because they feed on the remains of other creatures. Vultures may seem ubiquitous, but many birds of prey are threatened by habitat destruction and hunting as pests. One of the best examples is the Mauritius kestrel, the population of which—through habitat fragmentation, introduction of foreign species, and pollution caused by widespread use of pesticides— was down to four wild birds in 1974. However, thanks to the hard work of Carl Jones in Mauritius, by 1996 the number had climbed to about 400 total birds [See Solutions: Restoration of Habitats and Species].
NEW WORLD BIRDS
South America is sometimes called the "bird continent" for its diverse range of birds. This diversity can be partly attributed to the multitude of fruits which provide sustenance for the large number of fruit-eating birds including toucans, oropendulas, parrots, parakeets, tanagers, cotingas, and manakins.
One of the images conjured up when people think of the rainforest is a popular breakfast cereal image, the large, colorful bill of the toucan. About 40 species of toucans are distributed from Mexico to Paraguay and many are marked with bright contrasting colors including yellow, orange, red, blue, and white zones on the upper parts. Toucans are tree dwellers which usually nest at 65-100 feet (20-30 m) and feed on fleshy tropical fruits, and infrequently on insects and birds eggs. Their large bill is hollow, but still impedes flight which essentially consists of a leap from one tree, a few clumsy wing beats, a carefully planned landing, and a bit of luck.
Another beautiful New World bird is the quetzal from Central American forests, which was revered as a god by the Aztecs and Mayas. Quetzals pluck fruit in flight and bring it back to their perch for consumption. This small but voracious bird eats more than half its weight each day in insects, frogs, lizards, and snails. The quetzal is becoming rare with extensive deforestation in Central America.
Hummingbirds are an additional type of colorful bird found only in the New World, although they do have Old World counterparts, the sunbirds. They are the second largest bird family in the New World, with 320 species, and are some of the smallest birds in the world. The smallest species, the bee hummingbird, has a maximum size of two inches, half of which is tail and beak. Because hummingbirds use so much energy, with a heart rate from 450-1300 beats per minute, they must consume several times their body weight in nectar each day. In addition, hummingbirds conserve energy by falling into a comatose-like state at night. Their heart rate falls to 35-50 beats per minute at night and their body temperature approaches the surrounding temperature.
One of the strangest birds in the world is the hoatzin which jumps and climbs about in the canopy of South America. This chicken-sized bird has red eyes surrounded by bright blue skin and a crest of long thin feathers. The hoatzin is a clumsy flier that only flies when it must and then only for short distances. One of the most interesting aspects of hoatzin ecology is that young birds have a pair of claws on the bend of each wing. When confronted with danger, the young birds drop out of the tree into the water. They wait there until the danger has passed and climb back up to their nest with the help of their clawed wings. Adult birds have another means of defense; they can produce on offensive odor that drives enemies away. Hence its other common name, the stink bird.
Although most birds build their nests to conceal them from predators, two New World species, oropendulas and caciques, construct their nests in open areas so predators have to cross open ground, which few are willing to do. The long, hanging, basket-like nests are almost always constructed near a stinging bee, wasp, or ant nest which tends to deter potential predators, along with the parasitic botfly, the larvae of which lives under the skin of the chicks, feeds on its flesh, and can devastate an entire oropendula colony. Botfly larvae can also infest humans, and are an extremely nasty-looking parasite that is difficult to remove.
OLD WORLD BIRDS
The birds of the tropical rainforests of the Old World are nearly as diverse as those of the New World, and contain some stunning species. Among the most striking are the paradise birds of the Australasian realm and the hornbills of Africa, Southeast Asia, and New Guinea. The paradise birds from New Guinea and Australia are colorful birds with fantastic plumage; they were first considered divine creatures from heaven when early skins sent back to Europe had their feet removed and had such brilliant appearances. There are some 40 odd species of paradise birds, most of which are arboreal, live in mountain zones, and eat insects, small vertebrates, and fruit.
Another memorable group of birds are the hornbills, which are large (the helmeted hornbill may reach five feet (1.5 m). These noisy birds are represented by 45 species including the imposing rhinoceros hornbill of Sumatra, Borneo, and Western Java. This species has black plumage with a white tail and an enormous yellow beak with a casque--a horny sheath situated on the crown. The Rhinoceros hornbill has a remarkable nesting behavior in which the female holes up using mud in her tree hollow with her eggs, leaving only a tiny opening. She is entirely dependent on the male to bring her and her young fruits, snakes, lizards, and insects. If something happens to the male bird, she will die unless another, un-mated male comes to her rescue, which does sometimes occur. Like other hornbills, the rhinoceros hornbill is an important seed disperser in the tropical rainforest. Recent research on African hornbills by San Francisco State University suggests that the role of hornbills in forest regeneration is becoming even more important as deforestation spreads. Unlike primates and forest elephants, which will often not cross clearings, hornbills have a large range and will cross logged areas to disperse seeds in forest fragments.
One interesting groups of birds, the honey guides of Sub-Saharan Africa and Southeast Asia, are well-known for their habit of guiding humans and honey badgers to beehives. The bird calls when man or badger approaches, and flies off calling again until the man approaches again. It repeats this process until it is near a hive. Once the man opens the nest and takes the honey, the bird can then eat the wax, bees, and larvae.
Review questions:
- How many bird species are there in the world?
- What do parrots eat?
- What continent has the most species of birds?