Characteristics of Birds ENDOTHERMIC (warm blooded) 4 chamber heart Feathers Highly efficient respiratory system Lightweight/rigid skeleton Beak Hollow bones for flight Internal fertilization and hard-shelled amniotic egg

Evolution of Modern 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.

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Diversity of birds: major bird orders Struthioniformes: Ostriches Podicipediformes – Grebes (diving birds with lobed feet). 21 species. Gaviiformes – Loons. 5 species. Pelecaniformes. Pelicans

Great Cormorant Southern Cassowary

Pied-billed Grebe Common Loon

Diversity of birds: major bird orders Anseriformes – Waterfowl. Ducks, geese and swans. About 160 species. Falconiformes Hawks, eagles and falcons. Over 300 species Galliformes – chicken-like birds. Grouse, quail, turkeys. Over 250 species.

Ruffed Grouse Mallard Ducks American Kestrel Wild Turkey

Diversity of birds: major bird orders Ciconiiformes – Long-legged wading birds. Storks, herons, ibises, egrets. 120 species. Charadriiformes – Shorebirds and gulls. Plovers, sandpipers, stilts, auk, puffins, gulls and terns. Over 360 species. Columbiformes – Pigeons and doves. Over 300 species. Psittaciformes Parrots. More than 350 species

Razorbill White Stork Rock Dove Scarlet Macaw

Diversity of birds: major bird orders Strigiformes – Owls. About 180 species. Apodiformes – Short-legged acrobatic fliers. Swifts and hummingbirds. About 420 species. Piciformes – Woodpeckers. About 400 species.

Common Swift Barn Owl Pileated Woodpecker

Diversity of birds: major bird orders Passeriformes – Perching birds. Songbirds. Crows, warblers, cardinals, sparrows, starlings, etc. Over 5,700 species.

Cardinal European Starling

Feathers Among living animals feathers are 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 May have been used as a thermoregulatory device (Keeps them warm). 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.

Feather structure Feathers are made of keratin Keratin also found in hair, nails, claws and scales of other animals

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

Downy Feather

Feathers Body feathers include an aftershaft that emerges from the underside of the feather The aftershaft always downy and functions to increase insulation.

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 bones Bones hollow and supported by internal struts or spongy bone Reptilian tail lost. Fused tail bones (pygostyle) support tail feathers Teeth lost. Skull and bill light but strong.

Hollow bones reduce the overall mass of the bird. 19.6 Hollow bones reduce the overall mass of the bird. Less weight = less energy to fly

Adaptations for flight Skeleton strengthened ribs are rear-facing that overlap and strengthen walls of thorax bones of wrist, pelvis fused Sternum or breastbone enlarged Fused hand bones support and maneuver primary flight feathers. Efficient lungs and powerful four-chambered heart power flight.

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Further skeletal modifications for flight Furcula (wishbone) The clavicles are fused to form a structure The furcula flexs during flight and spreads and contracts during each wingbeat. The flexing enhances gas exchange by assisting in moving air through the air sacs.

Furcula (in red)

Further skeletal modifications for flight: arm and fingers The wing is supported by the arm and finger bones. The primary feathers attach to the wrist and finger bones Secondary feathers attach to the radius and ulna.

Legs joints and bones. When looking at a bird’s leg what appears to be the knee is actually the ankle. The adaptation of the feet can show what the bird eats

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Perching Being able to perch in trees was an early avian adaptation. The largest group of birds the Passerines (Passeriformes: perching birds) have four moderately long toes, three facing forward and one back. The tendons of the toes can lock the foot in a firm grip. Hence a sleeping bird does not fall off its perch.

Perching Song Thrush

Hopping and walking Most passerines hop in fact most cannot walk. However, some species that spend a lot of time on the ground such as larks and starlings can walk. In many other groups of ground-dwelling birds (e.g. chickens and their relatives) however walking is used.

Running A few birds are specialized for running and possess long legs. Ostriches have two toes and rheas three at the end of the limb

Climbing Various birds including woodpeckers, nuthatches, treecreepers and woodcreepers climb up and down tree trunks. The feet in all cases are strong and the toes usually well curved and the tail is often used as a brace to prop the body against the trunk.

Montane Woodcreeper Bennett’s Woodpecker

Swimming A wide variety of birds swim and webbing of the front toes The other adaptation to increase surface area for swimming is lobed toes.

Feeding and digestion: beaks Birds are not the only organisms with beaks as turtles and various dinosaurs possessed them too. However, birds have a tremendous diversity of beaks. The beak is a birds principal tool for handling food and its size and shape determine the foods that can be eaten.

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Beaks Birds such as crows and ravens have a general purpose bill that can handle lots of different foods. Raven

Beaks Finches possess short, deep bills that are ideal for opening seeds. House Finch

Beaks Crossbills have beaks in which the upper and lower mandibles cross. These are ideal for opening pine cones to reach the seeds Crossbill beak

Beaks Warblers have fine forceps like bills good for handling soft-bodied foods such as insects. Warblers also have specialized feathers to funnel insects to the mouth Magnolia Warbler

Beaks Dabbling ducks, such as mallards, have beaks that are good for straining water. However, ducks such as mergansers have beaks that are serrated and help in grasping fish.

Beaks Spoonbills and flamingoes possess bills similar to dabbling ducks that are good for sifting mud and water. Flamingo beak

Beaks Raptors, such as owls, hawks and eagles, possess short bills with a hooked tip that are ideal for dismembering prey.

Beaks Toucans and hornbills are both fruit specialists and their light, but long bills allow them to pluck distant fruit.

Beaks Skimmers have a compressed lower mandible that snap shut down on fish The bird flies over the water with the lower mandible skimming through the water.

Avian lung The metabolic demands of flight are high and to meet these demands The avian lung must be much more efficient than the mammalian lung. This is because the air flow is one-way, gases can be more efficiently exchanged and there is no “dead air” in the lungs The one-way flow of air is achieved by using a system of air sacs and a two breath cycle.

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Avian Circulatory System Birds have a 4-chambered heart Birds have very efficient cardiovascular systems that permit them to meet the metabolic demands of flight The cardiovascular system not only delivers oxygen to body cells Also plays an important role in maintaining a bird's body temperature.

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.

Bird’s digestive tract and other internal organs http://www.dkimages.com/discover/previews/824/80016755.JPG

Stomach The stomach a birds possesses is dictated by its diet. Birds that each high volumes of soft foods such as meat have extensible stomachs that can hold a lot of food. Those that have to process tough foods such as seeds and insects have much more muscular stomachs that help to grind the food.

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 thus fulfills the same role as the teeth in mammals. 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.

Intestines The main site of chemical digestion is the intestine where enzymes break down the food into small molecules that can be absorbed across the intestinal wall.

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. Puerto Rican Screech owl

Vision Bird eyes are similar in structure to those of other vertebrates, but the shape varies from a flattened sphere to tube-like. The variation is shape appears to be a result of the difficulties of fitting an enlarged eye into a more modest sized skull. By altering eye shape birds such as owls have avoided developing the disproportionately large heads they would have required if the eye were spherical.

Vision A unique feature of the avian eye is the presence of a comb-like structure called the pecten. The pecten arises from the rear of the eye close to where the optic nerve exits the eye. The function of the pecten remains unclear even after 200 years of investigation. The organ’s large blood supply suggests it may provide nutrition to the retina and perhaps remove metabolic wastes from the vitreous humor.

Vision A second interesting feature of avian eyes is the presence of colored oil droplets in cone cells. These act as filters absorbing certain wavelengths of light and allowing others through, but their exact function remains unclear.

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. The cochlea has about 10x as many hair cells per unit length than a mammalian cochlea does.

Hearing Owls possess the most acute hearing among birds Owls possess a distinctive facial ruff of stiff feathers, which focuses and amplifies sounds. Some ruffs are asymmetric and the ruff’s asymmetry which enhances the owls ability to isolate sounds in three dimensional space.

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.

Quiz 1) What does this bird live? 2) What does it eat?  5) What does this bird eat?