Perching Birds: Passeriformes
PERCHING BIRDS: Passeriformes
The order of Passeriformes, commonly called passerines (PASS-ur-eenz), are the largest and most unique family of birds. A few of the many birds in the passerine order are crows, finches, flycatchers, nightingales, swallows, tanagers, vireos, shrikes, wrens, and warblers. They are sometimes called "perching birds" and (less accurately) "song birds." These perching birds include some of the most colorful and mysterious of all birds in the world, such as birds of paradise from New Guinea and the bright orange cock-of-the-rock from tropical South America. They are generally small to medium in size (except for the crows, jays, and lyrebirds) with large wings relative to their body size. Two interesting physical features of the passerines are their distinctive syrinx (SIHR-ingks; or vocal organ) that allows them through complicated muscles to have a wide range of songs and calls, and their very specialized feet and legs that allow them to grip and move in very unique ways.
Passerines have three toes that point forward and one toe that points backward. The first toe, called the hallux (HAL-lux), is often called the hind toe because it always points backward and is never reversible. This arrangement allows them to perch on many different slender structures such as tree branches, grasses, telephone and fence wires, feeders, or anything that has some type of narrow place to perch. Their vocal organ allows the birds to produce a large range of vocalizations (although some species can only grunt and hiss while others produce very complex and melodic sounds that are called songs).
Bills on passerines vary greatly in size and shape due to the type of diet of each species. The types of bills range from tiny, needle-like bills of insect-easting warblers and vireos, to the generally huge, vise-like bills of finches, designed to crack the hard shells of seeds.
Passerines weigh between about 0.18 ounces (5 grams) in kinglets (also very small in weight are the bushtits and pygmy tits) to about 3.1 pounds (1.4 kilograms) in ravens and about 3.7 pounds (1.7 kilograms) in Australian lyrebirds and ravens.
Passerines are very widespread on all continents except Antarctica, but have the greatest numbers in the tropical areas of the world. They are considered the most widely distributed of all birds, living on nearly every oceanic island that can support a bird. Passerines include over half in total numbers of the known birds in the world.
Passerines are found in grasslands, woodlands, scrublands, forests, deserts, mountains, and urban environments. They are widely scattered throughout arid (dry) to wet, and temperate (mild) to tropical climates, especially liking areas filled with trees because most of the birds are arboreal; that is, they live primarily in trees. Although passerines are found in most areas of the world, they avoid areas with permanently frozen land, or permafrost, that are always covered with snow and ice.
Passerines eat mostly seeds, fruits, nectar, insects, small birds, small lizards, and marine invertebrates (animals without a backbone). They have been known to also eat carrion (decaying animals), and even potato chips and other foods left out by humans. They eat often throughout the day and need a high-energy diet in order to supply their active lifestyle. Crossbills, diggers, and swallows have shapes for their bill, wing, and legs that are especially adapted for foraging. They forage (search for food) by many different methods including taking insects from the bark of trees, catching insects as they fly through the air, and very specialized methods for eating seeds. Most of the birds eat food as they find it, but some do store their food to eat later. Shrikes (sometimes called "butcherbirds") use an unusual way to store foods they catch. They spear insects, small birds, and lizards on thorns or barbed wire, so they can come back later to feed.
BEHAVIOR AND REPRODUCTION
Because of their leg, foot, and toe arrangement, passerines are able to sleep while perched when special features in the foot automatically grip a perch. Being songbirds, passerines are very vocal birds with highly developed vocal chords. In fact, the birds are some of the most complex and rich singers in the bird world. They sometimes copy the songs and calls of other birds, especially the songs of competing males within their own species. Some species even copy the sounds of insects, frogs, and (even) mechanical sounds heard in their environment. Many passerines migrate from their nesting grounds to warmer regions, or from southern temperate regions north to the tropics. Predators (animals that hunt other animals for food) of passerines include raccoons, feral (wild) cats, and snakes.
There are many different ways that passerines build nests and many different materials that are used to construct nests. Generally, nests are made out of sticks or grass on the ground, in trees, and even sometimes in the banks of fast-flowing rivers. Nests are often camouflaged (KAM-uh-flajd; designed to hide by matching the colors and textures of the surrounding environment) in order to conceal them from predators. Although nests range from being built very simply to very elaborately, they can be classified as being constructed in three different ways: built out of a hole, built so the opening is from above, and built with a dome or roof.
PASSERINES VERSUS NON-PASSERINES
About 60 percent of all bird species are passerines, and the families within this order have a larger than average number of species. These two facts portray the degree of success with which passerine birds evolved and grew in numbers over the many, many years of their existence. Because there are so many passerines, the class Aves (birds) is often informally divided into passerines and non-passerines.
Parental care by both sexes is common in passerines, although females sometimes are left with all of the duties. Cooperative breeding, in which young birds delay breeding and assist other individuals (often their parents) in raising young and defending the territory, is common in several passerine groups. Female passerines lay small eggs that are usually colored or marked in some manner. Clutch size (group of eggs hatched together) varies greatly from one to sixteen eggs. Passerines are born blind, naked, and completely helpless. The incubation period (the time that it takes to sit on eggs before they hatch) is around fourteen days but can last up to twenty-eight days in large species and fifty days in lyrebirds. Some females are able to replace eggs that have been lost or destroyed. The fledgling period (the time necessary for young birds to grow feathers necessary to fly) is eight to forty-five days.
PASSERINES AND PEOPLE
Passerines help to control insects that destroy trees. In fact, the American redstart feeds on regal moths and the red-eyed vireo eats gypsy moths, both of which are very harmful to oak trees, a common tree found in urban areas.
Passerines are by far the most successful group of birds on Earth with respect to numbers and distribution around the world. More than five hundred passerine species, out of 5,100 to 6,000 species worldwide, are considered threatened with extinction, mostly due to habitat loss. (The exact number of passerine species is unknown due to disagreements among bird experts about whether some birds are species or not. About 8,600 total bird species are believed to exist throughout the world.) Bird experts, or ornithologists (people who scientifically study birds), believe that some of the species of passerines will become extinct in the future unless corrective measures are taken to preserve their habitat and reverse other negative conditions brought about mostly by human activities.
FOR MORE INFORMATION
del Hoyo, Josep, Andrew Elliott, Jordi Sargatal, Jose Cabot, et al., eds. Handbook of the Birds of the World. Barcelona: Lynx Edicions, 1992.
Dickinson, Edward C., ed. The Howard and Moore Complete Checklist of the Birds of the World, 3rd ed. Princeton, NJ and Oxford, U.K.: Princeton University Press, 2003.
Forshaw, Joseph, ed. Encyclopedia of Birds, 2nd ed. San Diego, CA: Academic Press, 1998.
Harrison, Colin James Oliver. Birds of the World. London and New York: Dorling Kindersley, 1993.
Perrins, Christopher M., and Alex L. A. Middleton, eds. The Encyclopedia of Birds. New York: Facts on File, 1985.