Modern Birds  The other remaining Archosaurs are birds given their own class Aves by traditional taxonomists.  There are approximately 8,600 species of birds ranging is size from the tiny bee hummingbird to the ostrich.

Bee hummingbird images/pho/t172/T172726A.jpg

Characteristics of the birds Feathers a unique character among living animals, but also found in dinosaurs. Feathers a unique character among living animals, but also found in dinosaurs. Endothermic Endothermic Skeleton modified for flight. Bones hollow, forelimbs support the wing, ribs with uncinate processes, beak but no teeth, reduced tail. Skeleton modified for flight. Bones hollow, forelimbs support the wing, ribs with uncinate processes, beak but no teeth, reduced tail. Breathing by lungs and associated air sacs Breathing by lungs and associated air sacs Internal fertilization and hard-shelled amniotic egg Internal fertilization and hard-shelled amniotic egg

Evolution of birds  Birds evolved from a group of theropod dinosaurs in the Jurassic period. The oldest known bird fossil is Archaeopteryx lithographica which has a mix of “reptilian” and avian features.  Reptilian: long tail, teeth, long clawed fingers  Avian: feathers, ribs with uncinate processes, avian shoulder girdle.

Archaeopteryx (oldest known fossil bird) Jurassic 150mya Size: Large chicken

Feathers  Among living animals feathers are a uniquely avian trait.  However, it is now well established that feathers also occurred in dinosaurs. In the 1990’s feathers were described from series of non-avian coelurosaurs, mostly from the Chinese Liaoning deposits.

Feathers  Feathers are what enable birds to fly, but originally are believed to have evolved as a thermoregulatory device.  Feathers are lightweight, but strong. The surface of the feather is made up of tightly spaced, overlapping filaments that hook together. Overlapping feathers form the wings with which birds fly.

Dinosaur feather impressions

Feather structure  Feathers are made of keratin: an inert substance that consists of insoluble microscopic filaments embedded in a protein matrix.  Keratin is the substance found in hair, nails, claws and scales of other animals, but bird keratin is unique and differs from that of modern reptiles.

Feathers  There are two main categories of feathers Plumaceous – downy for insulation Plumaceous – downy for insulation Pennaceous – linked, vaned feathers wing and contour feathers. Pennaceous – linked, vaned feathers wing and contour feathers.  Vane of a typical body feather consists of a hidden downy base (for insulation) and an exposed cohesive outer portion (for streamlining).

Downy Feather

Feathers  Body feathers of most birds include an aftershaft that emerges from the underside of the shaft where the first basal barbs of the vane branch off.  The aftershaft is almost always downy and functions to increase insulation. In ptarmigan winter plumage the aftershaft is ¾ as long as the main feather.

Aftershaft Ptarmigan:

Feather structure  A contour feather has a long central shaft and a broad flat vane. The hollow base of the shaft (quill) anchors the feather in a follicle under the surface of the skin.  The rest of the shaft, the rachis, supports the vanes. Branching off from the rachis are barbs. Each barb has barbules projecting to either side that interlock with the barbules of adjacent barbs.  Barbs and barbules form an interlocking, but flexible surface. 

19.4

Adaptations for flight  In general, the avian skeleton has been lightened and strengthened for flight.  This has been achieved by eliminating some structures and modifying others.

Adaptations for flight  Feathered wing.  Mass reduction Wrist bones reduced to two Wrist bones reduced to two Bones hollow and supported by internal struts or spongy bone Bones hollow and supported by internal struts or spongy bone Reptilian tail lost. Fused tail bones (pygostyle) support tail feathers Reptilian tail lost. Fused tail bones (pygostyle) support tail feathers Teeth lost. Skull and bill light but strong. Teeth lost. Skull and bill light but strong.

19.6 Bird’s Hollow Bone

Adaptations for flight  Skeleton strengthened ribs have rear-facing uncinate processes that overlap and strengthen walls of thorax ribs have rear-facing uncinate processes that overlap and strengthen walls of thorax bones of wrist, pelvis fused bones of wrist, pelvis fused  Sternum or breastbone enlarged with a large keel (carina) for attachment of massive flight muscles -- pectoralis and supracoracoideus.  Fused hand bones support and maneuver primary flight feathers.  Efficient lungs and powerful four-chambered heart power flight.

Video- skeleton:

Triosseal Canal. Human Bones of Shoulder

Furcula (in red)

Further skeletal modifications for flight  Furcula The clavicles are fused to form a structure called the furcula or wishbone.  The furcula flexs during flight and spreads and contracts during each wingbeat. The flexing may enhance gas exchange by assisting in moving air through the air sacs.  bliss.com/bird-flight.html bliss.com/bird-flight.html bliss.com/bird-flight.html

Bernoulli’s Principle - “When the speed of a fluid (air) increases, internal pressure in the fluid decreases” FLIGHT

Shape of bird’s wing = airfoil The high pressure above the airfoil will be greater than the low pressure above the wing, causing the bird to “lift” causing the bird to lift up.

Lift and thrust  In order to fly both horizontal thrust and vertical lift are required.  Thrust is mainly generated by the primary feathers (the long ones at the end of the bird’s hand), which on the downstroke twist and acting like a propeller push the air backwards.  Lift is mainly generated by the secondary feathers (the inner portion of the wing), which form an airfoil. (Peregrin Falcon with camera attached in flight)

e.com/watch?v=E UEZkwJulBY Hand –feeding hummingbirds in Alaska

Avian lungs  The one-way flow of air is achieved by using a system of air sacs and a two breath cycle.  On inspiration air flows down the trachea to air sacs below the lung. On expiration the air mass flows into the lung where gas exchange takes place.  With a second inspiration the air mass in the lung flows into anterior airsacs and with a second expiration exits the body via the trachea.

Raven: /jpegs/raven.jpg

Magnolia Warbler

House Finch

Crossbill beak jpg/_ _malecrossbill203rspb.jpg

Bird’s digestive tract and other internal organs

Feeding and digestion  Because birds lack teeth they can’t process food much in the mouth so that is left up to the gastric system.  Birds can frequently gather food faster than it can be processed. This food is usually stored in the birds crop, an enlarged part of the esophagus.  The crop is also used to store food that will later be regurgitated to chicks.

Stomach  A bird’s stomach has two parts the anterior glandular proventriculus and the posterior gizzard.  The proventriculus contains glands that secrete digestive enzymes. In birds that swallow whole foods such as fruits the proventriculus is often very large.

Gizzard  The gizzard’s main function is to mechanically process food.  The walls of the gizzard are thick and muscular and the gizzard often contains small stones, which the birds swallow to assist in grinding the food. The gizzard thus fulfills the same role as the teeth in mammals.

Gizzard  The gizzard can exert significant pressure. For example, a turkey’s gizzard can process two dozen walnuts in about four hours.  It can also crack hickory nuts, which require kg of pressure to break.

Seasonal changes in gut morphology  Birds often change their diets over the course of a year and gut morphology changes too. Insects are more easily and quickly digested than plant food (e.g. berries).  When starlings switch to eating more plant material in the fall their intestines increase in length by about 20% and decrease by a similar amount in spring when their diet switches back to animal prey.  Accompanying the morphological changes are changes in the types and quantities of digestive enzymes produced tailored to match the composition of the diet.

Sensory systems: vision  Most birds have excellent vision and this is reflected in the structure of the brain. There are large optic lobes and the midbrain which processes visual information is enlarged.  In contrast, in most birds olfaction is unimportant and the olfactory bulbs are small.

Hearing  Birds have hearing that is comparable in sensitivity to that of humans even though their heads are much smaller.  However, they have proportionally much larger tympanic membranes which enhances sensitivity to sound. In addition, the cochlea has about 10x as many hair cells per unit length than a mammalian cochlea does.

Puerto Rican Screech owlSaw –whet owl wildlife-facts_images_2003/pr_screech_owl.jpg

Hearing  Owls possess the most acute hearing among birds (comparable to that of a cat) and can isolate sounds very accurately even in complete darkness.  Owls possess a distinctive facial ruff of stiff feathers that acts as a parabolic sound reflector, which focuses and amplifies sounds.  Some ruffs are asymmetric and the ruff’s asymmetry (as well as asymmetry in the vertical placement of the ears) enhances the owls ability to isolate sounds in three dimensional space.

Barn owl newmelones/images/wildlife_barn_owl.jpg

Hearing  The asymmetries in the ruff and ears cause delays in the time at which sounds reach each ear that can be interpreted by the brain and used to identify precisely the source of a sound.  A barn owl’s ability to do this is so good that it can isolate sound to within 1º in three dimensional space. If you envisioned yourself surrounded by a sphere with a radius approximately equal to your arm length 1º would be about the area covered by a fingertip.

Olfaction  Most birds have a poorly developed sense of smell, but a few groups do have a good sense of smell.  These include kiwis which have their nostrils at the end of the bill and use odor cues to find prey when they probe in the earth.

Brown Kiwi hatched at the Smithsonina National Zoo 2006: Kiwi’s,the flightless birds that are the national symbol of New Zealand, appear to sniff out their earthworm prey. (nocturnal)

Olfaction  Other birds with a good sense of smell are the various “tubenoses” the petrels, shearwaters and albatrosses, which are attracted to the scent of chummed fish and fish from a considerable distance.  In addition, turkey vultures have a well developed sense of smell and can find even covered carcasses very quickly.

Sooty Shearwaters and Nothern Fulmars are attratcted from downwind to the smell of fish oils, squid, and krill.

Turkey Vulture: AC_Turkey%20Vulture%20Head%20Shot%20from%20MDC.jpg

European Starling Cardinal RmP1nuxW8II/AAAAAAAAAHM/SCIyggloewY/ s400/cardinal.jpg