Birds of Seabrook Island



  Black and Least Terns

Species Acct.
NW Warblers


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What is a bird?
Origin of Birds
Distribution in Time and Space


What is a Bird?

  Birds are vertebrates (animals with back-bones). They belong to the Class Aves. Other vertebrates include the cartilaginous and bony fishes, amphibians, reptiles, and mammals. Birds are air-breathing, bipedal, homoiothermic (they maintain a relatively high and constant body temperature), and  they lay eggs for which they provide some degree of parental care. Their most obvious traits are that they have feathers and most are able to fly. Modern birds lack teeth and have a strong but light (and often pneumatic) skeleton that reduces its mass. They have a four-chambered heart (which is not completely homologous to the mammalian four-chambered heart) and an active metabolism. Most species are active during the day (diurnal) and are vocal and social creatures so they are more obvious to us than many other vertebrates. Birds are a diverse group with ~10,000 species.

Origin of Birds

  The best-known fossil bird is Archaeopteryx. It was discovered in 1862 and contributed to the early debate about evolution (Darwin's The Origin of Species was published in 1860). Eleven specimens have been described to date - all coming from southern Germany where fine-grained lithographic slate has been mined over the years. Archaeopteryx lived in the Late Jurassic, about 150 million years ago. Europe consisted of a series of islands surrounded by warm tropical seas. Archaeopteryx was a crow-sized bird with flight feathers that were essentially modern in appearance (their bodies were probably not sheathed in contour feathers). The hind legs also bore feathers that may have assisted in flight. However, they did not have the keeled sternum used by modern birds to anchor their massive flight muscles so there has been a debate about whether they were simply gliders assisted by a weak downstroke of the wings or could show true powered flight. They also differed from modern birds in the possession of teeth. Flight feathers of the tail attached to separate vertebrae rather than the fused "pygostyle" of modern birds (and the longer tail and heavier head probably provided a balance around their center of gravity to promote gliding/flight). They also had clawed fingers on their hand.
   Whatever Archaeopteryx's position is in the origin of birds, it displays a number of features common to reptiles, specifically a group known as theropods (Maniraptora, including dromaeosaurs and oviraptors). In recent years, Liaoning Province in northeastern China has yielded a plethora of theropods, many with feathers (some authors even suggest that Tyrannosaurus rex had feathers)... An alternative theory derives birds and the maniraptors from early archosaurs (Alan Feduccia, Larry Martin, and others). WIKI
   Whatever the exact origin of flying reptiles ("birds") may have been, birds diversified into a wide variety of forms in the Cretaceous. Apparently teeth were lost independently in several lines. The Pygostylia included more modern forms in which the caudal vertebrae fused to form a pygostyle (used to anchor the tail feathers). According to Chiappe, 2007, sister groups of the Pygostylia included Confuciusornithidae and Ornithothoraces.
   Confuciusornis was a crow-sized bird from the Early Cretaceous. It was toothless and has a pygostyle. The sternum was small (with a slight keel?) but the scapulae were fused to the coracoids on each side of the thorax and may have provided a platform for the attachment of flight muscles. It retained claws on the forelimb. Primaries were long but secondaries were quite short giving it an oddly-shaped wing.
   The Ornithothoraces included the Enantiornithes and Ornithurae.
   Enantiornithes were the most diverse birds of the Mesozoic - most retained teeth and claws on the hand. They were a diverse group with more than 40 described species and ranged from sparrow-sized birds to Avisaurus with an estimated wing span of 4'. They appeared to occupy a variety of niches and included swimmers, waders, seed eaters, and carnivores that fed on small dinosaurs. The Ichthyornithes were an advanced group of gull-like enantiornithines that became specialized fish-eaters. Along with all dinosaurs and many other vertebrates, this group became extinct at the Cretaceous-Tertiary boundary (supposedly as the result of a meteor impact).
   The Ornithurae included the Hesperornithiformes and Neornithes.
   Hesperornithorniformes (also lost at the K-T boundary) were toothed, fish-eating birds of the Northern Hemisphere. Although smaller species may have been able to fly, Hesperornis and Baptornis had vestigial wings and were foot-propelled divers. Their simple teeth were set in a groove along the jaw and aided in holding fish. It has been suggested that the group may have come from toothless ancestors and re-evolved their unique teeth.
   All modern birds are included in the Neornithes. (1) The Eoaves or Paleognathae, named for the primitive structure of their palate, include large flightless or nearly flightless birds found on many of the world's continents. After considerable debate, it does appear that these birds are related. They include the Struthioniformes (ostrich, rheas, cassowaries, emus, and kiwis) and the Tinamiformes (tinamous). The first group are also called "ratites" - their sternum lacks a ventral keel for the attachment of flight muscles. Tinamous are very weak fliers with obvious relations to the ratites. There are 59 species of living Eoaves. (2) All other living birds are included in the Neoaves or Neognathae ("modern palate").


  The Neoaves include 9,615 species (Sibley and Monroe, 1990). They divide this group into 19 orders, 18 of these (and the Eoaves) are often referred to as "non-passerines" or birds other than "perching birds." There are 3,960 species of "non-passerines" in the Neoaves. The largest order of neoaves, the Order Passeriformes, includes 5,712 species of "perching birds" - birds with three toes directed forward and one backward with a special locking mechanism that facilitates perching.
   In developing linear lists of species, biologists attempt to "order" the lists from more primitive to more advanced forms. There are two problems with this - first, one must try to determine which groups are more primitive; and second, the relations among groups is not really linear. Instead, relationships are clustered - if you have a branch and draw a plane (section) through it at some distance from the trunk, you will have some twigs closer to others and some farther away - but it is not always evident where these twigs branched from the limb and branches from parallel limbs may well intertwine further complicating the picture. Moreover, the picture seen in the plane passing through the twigs is by no means linear - what do you list first?
   Early studies of avian systematics emphasized structures - the palate, skeleton, arterial patterns, muscle groupings, etc. They led to a traditional sequence of modern birds beginning with the loons, Order Gaviiformes, followed by grebes, the tube-nosed swimmers, etc, This sequence has been followed for years and the inference is that loons are really primitive birds, but are they?
   Sibley and Ahlquist, 1990, used DNA hybridization - a molecular technique - to examine as many birds of the world as they could. The outcome of their studies led them to begin their list with cracids (guans, chachalacas, curassows), megapodes (megapodes, scrub-fowl, brush-turkeys), and galliform-birds (pheasants, Old World quail, grouse, guineafowl, New World quail) and waterfowl (Anseriformes). Beginning classifications with the "Galloanserae" has gained considerable support.
   However, I've kept to the more traditional order in this web because our use of classification is probably enhanced by a "standard" arrangement and it matches most field guides (including Sibley's). However, if you contrast a loon - a specialized diver and fish-eater which cannot even walk on land - with a chicken - a generalized walking, flying bird that eats anything - it is easy to pick the chicken (or better, Red Jungle Fowl, Gallus gallus, with all its domestic variants) as the archetypical bird.

Distribution - Time and Space

    At the beginning of the Mesozoic, around 180 MYBP (million years before the present), the land masses of the world formed a large supercontinent (Pangea) with Laurasia to the North, Gondwanaland to the south and a broad embayment on the east, the Tethys Sea. In the Triassic (the first period of the Mesozoic), North American and Gonwanaland separated and Mexico became uncoupled from South America and eastern parts of North America separated from the Moroccan bulge of Africa. Throughout the Jurassic, Laurasia remained intact and sea-floor spreading was more rapid in the central and northerly regions of the newly formed Atlantic Ocean. South America remained attached to Africa (Gondwanaland). A second stage in the break-up of Pangea involved rifting between southern Africa and Antarctica. This rift extended northward between Africa and India which then separated from Antarctica/Australia and moved northward (to eventually impact Laurasia). In a third stage, the Atlantic rift extended northward and Eurasia rotated clockwise to enclose a portion of the Tethys Sea (forming the Mediterranean). By the end of the Jurassic, a breach split South America away from Africa, creating a long seaway. Australia and Antarctica remained connected, but the Indian sub-continent was moving northward toward Laurasia. By late Cretaceous, 70 MYBP, South America was completely separated from Africa and Greenland was separating from Europe but northeastern North America remained attached to Greenland and northern Europe. Stage four occurred in the early Cenozoic and completed the separation of North America and Eurasia. Australia and Antarctica separated only about 45 MYBP. (Australia is now moving northward, impacting southeastern Asia).
   During the Mesozoic, a diversity of reptiles and birds experimented with various body plans (teeth, long/short tails, feathers, and flight). The K-T boundary which saw the extinction of large dinosaurs (and many other creatures) set the stage for the evolution of modern birds extending over the past 40 million years (with most modern species evolving within the last million years). The distribution of some birds such as the "ratites" may be tied to continental drift. However, modern patterns are more likely related to centers of origin with barriers to dispersal between them - the Australian area and Laurasia - than to continental movements.
   Detailed ranges for all living species of birds are given in Sibley and Monroe (1990). Ranges of North American birds are given in the AOU Checklist and general ranges are suggested in Clement's Birds of the World. Many of our species also occur in other parts of the world and some our our species came from other parts of the world (they were introduced or invaded under their own power). Many related species may also be concentrated in one or another region of the world - perhaps the center of their origin and radiation? Several terms recognize these regions and are commonly used to describe the distribution of a group or species.
   New World
      North America - Nearctic
      South America - Neotropic
   Old World
      Eurasia - Palearctic
      Africa - Ethiopian
      South-east Asia - Oriental
   Australia and New Guinea - Australo-Papuan
   Holarctic = Nearctic + Palearctic
   Pantropical = the world's tropics (not many groups are pantropical)
   Cosmopolitan - universal distribution (minus Arctic and Antarctic ice caps)
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