Class Aves – BirdsBirds (class Aves) are archosaurs butalmost every feature of their reptiliananatomy has undergone modification intheir adaptation to flight.
Class Aves – BirdsBirds are found in most every habitatfrom forests to deserts, even in caves. Some birds dive in the ocean to 45 m tocatch prey. Birds have visited both the North & Southpoles. The bee hummingbird of Cuba weighs 1.8 gand is one of the smallest vertebrateendotherms.
Derived Characters of Birds A bird’s most obvious adaptations for flight areits wings and feathers. Feathers are the feature that set birds apartfrom other vertebrates.
Derived Characters of BirdsSome other theropod dinosaurs hadfeathers, but they were not capable ofsupporting flight. Insulation – provides support for the ideathat some dinosaurs were endotherms. Bright colors may have been used to attractmates.
Characteristics of Birds All birds also have hindlimbs adapted for walking,swimming, or perching. Foot structure in bird feetshows considerablevariation. All have keratinized beaks. All lay shelled amnioticeggs.
The Origin of Birds Archaeopteryx The oldest bird known. Skull similar to modern birds but with thecodontteeth. Wings with feathers were present.
The Origin of Birds Much of the skeleton wasthat of a theropoddinosaur. Long bony tail Clawed fingers Abdominal ribs S-shaped, mobile neck This fossil demonstratedthe connection betweentheropods & birds.
Living Birds The ratites, superorderPaleognathae, are allflightless. Primitive archosaurpalate. Ostriches, emus, rheas,kiwis, tinamous. Flat sternum, poorlydeveloped pectoralmuscles.
Living Birds All other birds have a flexiblepalate. The demands of flight haverendered the general bodyform of many flying birdssimilar to one another. Flying birds have a keeledsternum with well developedpectoral muscles.
Living Birds Flightlessness hasevolved in many groupsof birds. Penguins (use wings toswim through water). Many fossil formsincluding flightless owls,pigeons, parrots,cranes, ducks, & auks. Usually occurs onislands with fewpredators.
Form & Function – Feathers Feathers are lightweight,yet tough, consisting of: A hollow quill emergesfrom the skin. This becomes the shaftwhich bears numerousbarbs that form a flat,webbed surface, thevane. Each barb containsmany barbules.
Form & Function – Feathers Contour feathers are vanedfeathers that cover andstreamline a bird’s body. Called flight feathers if theyextend beyond the body. Down feathers are soft andhave no hooks on barbules. Filoplume feathers are hair-like – function unknown. Powder-down feathersdisintegrate as they grow,releasing powder that aids inwaterproofing.
Form & Function – FeathersFeathers are homologous to reptiles’scales.It develops from an epidermal elevationoverlying a nourishing dermal core. In reptiles, this elevation flattens into ascale. In birds, it rolls into a cylinder and sinks intothe follicle from which it will grow.
Form & Function – Feathers As a feather nearsthe end of its growth,keratin is depositedto make some of thestructures hard. The protectivesheath surroundingthe new feather splitsopen, and the featherunfurls.
Form & Function – FeathersWhen fully grown, feathers are dead –like mammalian hair.Birds molt to replace worn out feathers. Usually feathers are discarded gradually toavoid bare spots. Flight feathers & tail feathers are lost inpairs to maintain balance. Many water birds lose all their primaryfeathers at once and are grounded duringthe molt.
Form & Function – FeathersColors in birds may be pigmentary orstructural. Red, orange, & yellow are colored bypigments called lipochromes. Black, brown, & gray are produced by thepigment melanin. Blue is created structurally by the scatteringof shorter wavelengths of light by particleswithin the feather.
Form & Function – SkeletonA light, yet still strong skeleton is arequirement for flight. Bird bones are laced with air cavities.
Form & Function – SkeletonBirds are archosaurs, and had ancestorswith diapsid skulls. Bird skulls are highly specialized – mostlyfused into one piece.Leg bones in birds are heavier – thishelps lower the center of gravity givingaerodynamic stability.
Form & Function – SkeletonModern birds are toothless. Instead they have a keratinized beak.Most birds have kinetic skulls. They have a wide gape. Upper jaw is attached loosely increasing thegape.
Form & Function – Skeleton All birds that can flyhave a large, thinkeel on theirsternum thatprovides area forthe large flightmuscles to attach.
Food & FeedingEarly birds were carnivorous, feedingmostly on insects. Many birds are still insectivores. Other foods include nectar, seeds, berries,worms, crustaceans, molluscs, fish, frogs,small birds & mammals.
Food & FeedingSome birds are generalists, feeding on awide range of food items. Perhaps more competition for food, but lessdanger of something happening to the foodsource.Others are specialists, only feeding onone type of food. Less competition, more danger of losing thefood source.
Food & Feeding The beaks of birds are strongly adapted tospecialized food habits.
DigestionAt the end of the esophagus of manybirds is the crop. Used for storage.
DigestionThe stomach has two compartments: The first secretes gastric juices. The second, the gizzard, is lined withkeratinized plates that serve as millstonesfor grinding food. Birds swallow small stones to help this process.
DigestionOwls can’t digest the bones & fur orfeathers of their prey. These materials are bundled together andejected through the mouth. Owl pellets can be used to determine whatthe owls in a particular area have beeneating.
Circulatory SystemBirds have a four-chambered heart. Separate systemic and respiratorycirculations.Fast heartbeat – faster in smaller birds.Red blood cells are nucleated andbiconvex. Mammals are enucleated and biconcave.
Respiratory SystemThe highly adapted respiratory systemof birds is adapted for the high metabolicdemands of flight. The finest branches of the bronchi aredeveloped as tubelike parabronchi throughwhich air can flow continuously – instead ofending in saclike alveoli as in mammals.
Respiratory System There is anextensive systemof nineinterconnecting airsacs that connectto the lungs. Air flows to theposterior air sacs,to the lung, thento the anterior airsacs and out.
Respiratory SystemThe result is that there is an almostcontinuous stream of oxygenated airpassing through the highly vascularizedparabronchi.
Excretory SystemUrine is formed in large, pairedmetanephric kidneys. There is no urinary bladder. Nitrogenous wastes are secreted as uricacid rather than urea. Bird kidneys can only concentrate solutes to4-8 times that of blood concentration.
Excretory System Some birds,including marinebirds, have a saltgland to help rid thebody of excess salts. Salt solution isexcreted from thenostrils.
Nervous System Birds have welldeveloped cerebralhemispheres,cerebellum(important forcoordinatingmovement &balance), and opticlobes.
SensesBirds usually have poor sense of smell &taste. Some, carnivores, waterfowl, flightless birdshave well developed sense of smell & taste.Birds have the keenest eyesight in theanimal kingdom and also very goodhearing. A hawk can clearly see a crouching rabbit amile away!
FlightTo fly, birds must generate lift forcesgreater than their own mass and theymust provide propulsion to moveforward.Bird wings are designed to provide lift.
Flight - Wings are Specialized forParticular Kinds of Flight Elliptical wings are good for maneuvering in forests. High speed wings are used by birds that feed duringflight or that make long migrations. Dynamic soaring wings are used by oceanic birds thatexploit the reliable sea winds. High lift wings are found in predators that carry heavyloads. Soaring over land with variable air currents.
Migration Many species of birdsundergo longmigrations using wellestablished routes. Some species makethe trip quickly,others stop along theway to feed. Often, they followlandmarks such asrivers and coastlines.
Migration The stimulus formigration has to dowith changinghormone levelsbrought about by achange in daylength.
MigrationBirds navigate using a number of cues: Visual cues – landmarks. Accurate sense of time. Some may use the Earth’s magnetic field. Celestial cues – sun by day, stars at night.
Social Behavior – Mating Systems Two types of matingsystems found inbirds: Monogamy wherean individual hasone mate. Rare in animals,common in birds. Seasonal or lifelong
Social Behavior – Mating SystemsBirds have a high incidence ofmonogamy because both parents areequally able to perform most aspects ofparental care. Often success of the hatchlings requirescare from two parents.
Social Behavior – Mating SystemsPolygamy where an individual has morethan one mate during a breedingseason. Polygyny – one male, many females Polyandry – one female, many males
Social Behavior – Mating Systems The most commonform of polygamy inbirds is polygyny. In some species, suchas grouse, malesgather in a displayarea or lek. Eachmale defends part ofthe lek and displaysfor the females. Only females care foryoung. http://www.youtube.com/watch?v=s2_wdMmEupQ
Social Behavior – Mating SystemsAn example of polyandry occurs inspotted sandpipers. Females defend territories and mate withseveral males. Each male incubates a nest of eggs in thefemale’s territory and does most of theparental care.This system may have evolved inresponse to high predation rates.
Nesting Most birds build nestsin which to lay eggs. Often great care istaken to hide the nest,or make it inaccessibleto predators. When the young hatch,they usually must befed by one or bothparents.
Nesting Precocial young, such asducks, water birds, fowland quail are coveredwith down when theyhatch and can run orswim as soon as theirdown dries. Most precocial youngmust still be cared for bythe parents for a time.
Nesting Altricial young are naked andunable to see or walk athatching. They must remain in the nestfor a week or more. Parents must spend lots oftime & energy bringing foodto hatchlings. There is a continuum with theyoung of many species fallingin between the two extremes.