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Vertebrate Evolution
Z Phylum Chordata characteristics – may be with organism its entire life or only during a certain developmental stage
1. Dorsal, hollow nerve cord
2. Flexible supportive rod (notochord) running along dorsum just ventral to nerve cord
3. Pharyngeal slits or pouches
4. A tail at some point in development
Z Phylum Chordata has 3 subphyla
W Urochordata – tunicates
Z Adults are sessile marine animals with gill slits Z Larvae are free-swimming and possess notochord and nerve cord in muscular tail Z Tail is reabsorbed when larvae transforms into an adult
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W Cephalochordata –lancelets
Z Small marine animals that live in sand in shallow water
Z Retains gill slits, notochord, and nerve cord thru life
W Vertebrata – chordates with a “backbone”
Z Persistent notochord, or vertebral column of bone or cartilage
Z All possess a cranium
Z All embryos pass thru a stage when pharyngeal pouches are present
Lamprey ammocoete
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Jawless Fish
Hagfish Lamprey
Vertebrate Evolution 1. Tunicate larvae
2. Lancelet
3. Larval lamprey (ammocoete) and jawless fishes
4. Jaw development from anterior pharyngeal arches – capture and ingestion of more food sources
5. Paired fin evolution A. Eventually leads to tetrapod limbs B. Fin spine theory – spiny sharks (acanthodians) had up to 7 pairs of spines along trunk and these may have led to front and rear paired fins
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Z Emergence onto land
W Extinct lobe-finned fishes called rhipidistians seem to be the most likely tetrapod ancestor
Z Similar to modern lungfish and had gills and probably lungs to breathe air
Z Teeth and limb bones closely resemble early amphibian bones
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W Modern “walking” fish include walking catfish, mudskippers, and lungfish
Lungfish – found in Mudskipper South America, Africa, and Australia
Walking catfish – from southeast Asia but now found in Florida
W Earliest known amphibians were labyrinthodonts
Z Had traits of lobe-finned fish and later tetrapods
Z Most modern salamanders still cannot fully support themselves with their limbs and have unshelled eggs like fish
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Z Evolutionary timeline:
W Jawless fish – Cambrian Period (530 MYA) W Jawed fish – explosion of fish diversity in Silurian Period (425 MYA) W Terrestrial amphibians – Devonian Period (400 MYA)
Z Adaptations of some lobe-finned fish that allowed emergence onto land:
1. Limbs with digits 2. Lungs 3. A primitive neck
Z Fish-like ancestors probably evolved these traits in shallow swamps with stagnant water
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W Competition and an abundance of unexploited resources may have drove vertebrates onto land
W Another theory is that early amphibians lived and fed in water but deposited eggs in moist places on land for better survival of eggs and larvae
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W The amniotic egg: reptiles, birds, mammals
Z Carboniferous Period (320 MYA)
Z To this day, amphibian eggs are still very similar to those of fish and must be placed in moist areas to develop with no protective shell
Fish Frog
Z Seems to have developed to increase protection of terrestrial eggs from microbes
Z First, a fibrous shell evolved then, as added protection, a calcerous layer was added
Z All modern-day reptiles deposit calcium crystals in a fibrous matrix
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Z Today, most reptile eggs must absorb moisture from the environment to complete development
Z It is not clear whether extraembyronic membranes evolved within primitive eggs or female’s oviducts
Z Earliest amniotes were a group of labyrinthodonts called anthracosaurs (below)
Z Amniotes – extraembryonic membranes
W Do not need water to reproduce, no larval stage
W Chorion, amnion, and allantois provide metabolic support for developing embryo
W Yolk sac provides food
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Z Early reptiles – Carboniferous Period (300 MYA)
W During this time, plants were becoming abundant and diverse on land providing a food source
W Until then, vertebrates were primarily carnivorous, as most living primitive fishes (catfish, lungfish, gar, bowfin) and amphibians are today
Z The only terrestrial animal prey available was fast- moving invertebrates (spiders, centipedes, and mites)
Z An explosion of reptile species began (adaptive radiation) when they became herbivorous
Z Earliest reptiles were cotylosaurs, represented by Hylonomus which still had many amphibian-like traits such as its skull, limbs, and girdle
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Therapsida – the earliest mammals Permian Period 250 MYA
Reptiles to Birds
W Earliest known bird is Archaeopteryx lithographica which lived 155 MYA
W Range in size from a 2 gram hummingbird to a 100,000 gram ostrich (200-300 lbs.)
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Z Similarities:
1. Both have single occipital condyle which attach the skull to the vertebral column in a ball-and-socket fashion (mammal 2)
2. Both have a simple middle ear with one ear bone, the stapes (mammals have 3 middle ear bones)
3. Both have lower jaws composed of 5 or 6 bones on either side (mammal jaws are 1 bone)
4. Scales on the legs of birds are similar to reptile scales
5. Both lay shelled eggs
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6. In both, females have the hetergametic sex chromosome combination ZW (in mammals, it’s the males that have this condition with XY combination)
7. Both have nucleated red blood cells (mammals lack nuclei in red blood cells)
Z Fossil record
W 5 complete Archaeopteryx fossils have been found, all from central Europe, that date from 135-155 MYA during the Jurassic period when Europe had a tropical climate
W It was a crow-size, bipedal “reptile” with a blunt snout and small reptilian teeth
W Paleontologists believe it was similar to modern strong- running, terrestrial birds that could leap into trees and make short flights between branches and trees
W Primary wing feathers were asymmetrical as with modern birds capable of flight
Z Flightless birds have symmetrical vanes
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Possible Feather Evolution
Possible Reptilian Ancestors
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Z Today, birds have evolved into many forms to utilize different food resources in different habitats (adaptive radiation)
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Class Aves
1. Warm-blooded, endothermic, homeotherm
2. Descended from bipedal, lizard-like reptiles
a) Lay eggs b) Have scales on beaks and legs c) Feathers are specialized scales
3. Highly variable size: largest is ostrich (330 lbs) and smallest is scintillant hummingbird (0.08 oz.)
4. Adaptations to flying (all geared toward high power and low weight)
a) Mostly hollow bones with strut supports (some birds’ feathers weigh more than skeleton)
b) Fused bones - hip girdle with sacral vertebrae, hand bones of wings are absent or fused
c) Breast bone (sternum) modified into keel for attachment of large flight muscles
d) Feathers are extremely well-suited for insulation, streamlining, weight reduction, and flight
5. About 9,020 species worldwide and about 400 species that are found in MS, including migrants
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Z Bird are very diverse with:
W 31 Orders W 186 Families W 2,029 Genera
Z We will cover 22 Orders
Z Order Rheiformes - rheas
W Family Rheidae - all in one family; only 2 species
Z Largest living New World birds (5 ft, 50 lbs)
Z Flightless and live in grasslands of South America
Z Order Struthioniformes - ostrich
W Family Struthionidae - 1 sp. living
Z Largest living bird (8 ft, 300 lbs) Z Flightless and lives in grasslands of Africa
Z Order Casuariiformes – large flightless birds of New Zealand and Australia
W Family Casuariidae – cassowaries (3 species)
W Family Dromaiidae - emu (1 sp.)
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Z Order Dinornithiformes - kiwis
W Family Apterygidae - 3 living species
Z Short, stocky, flightless birds of New Zealand Z Forage at night on the ground for invertebrates and roost and nest in burrows Pied-billed grebe
Z Order Podicipediformes - grebes
W Family Podicipedidae - only family with 21 species
Z Foot-propelled diving birds Z Occur worldwide with one in MS (pied-billed grebe)
Z Order Sphenisciformes - penguins
W Family Spheniscidae - only family with 18 spp
Z Occurs only in southern oceans and northern limit is Galapagos Islands on the equator off of Ecuador
Z Wing-propelled diving birds that eat fish
Z The emperor penguin can dive to 900 ft. and stay under for over 20 minutes Emperor
Galapagos
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Z Order Pelecaniformes - pelicans, cormorants, snake birds W Long beaks with throat pouches that hold fish W Nest in large colonies Anhinga
W Family Pelecanidae – pelicans Brown pelican Z 8 species worldwide and 2 in MS (brown, American white)
W Family Phalacrocoracidae – cormorants Z 33 species worldwide, 1 in MS (double-crested) Z Once was rare but now common and a nuisance for catfish farmers
W Family Anhingidae - snake bird/anhinga/water turkey Z 4 species worldwide and 1 in MS
Z Order Ciconiiformes - herons, egrets, stork, ibis, spoonbill
W Long-necked and long-legged waders
W Nest in colonies along shores and marshes
W Family Ardeidae - herons, egrets, and bitterns
Z 64 species worldwide, 12 in MS
W Family Ciconiidae - storks, 1 species in MS (wood stork)
W Family Threskiornithidae - ibises and spoonbills, 3 species in MS (white and glossy ibis and roseate spoonbill)
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Roseatte spoonbill Tricolored heron
Scarlet ibis
Bittern
Wood stork
Z Order Anseriformes
W Family Anatidae - ducks, geese, and swans
Z Broad bills with many tactile nerve endings Z Body covered in down and oily feathers Z 158 species worldwide, about 26 in MS
Canada goose
Mute swan Canvasback
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Z Order Falconiformes – vultures, eagles, hawks, falcons
W Diurnal birds of prey with strong bill that is hooked at tip and feet with sharp curved talons
W Family Cathartidae – vultures
Z Carrion eaters/scavengers Z 7 spp worldwide and 2 in MS (black and turkey vulture)
W Family Accipitridae - eagles, hawks, kites, and harriers Z Large avian predators with 217 spp worldwide and 9 in MS
Griffon vulture Sea eagle
W Family Pandionidae – osprey Z Only 1 species in the world (common in MS)
W Family Falconidae – falcons Z 62 species worldwide and 3 in MS
Osprey
Peregrine
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Z Order Galliformes - quail, pheasants, turkey, “chicken”
W Vegetarian (granivorous) birds with short, stout beaks and short rounded wings W Strong feet and legs adapted to scratching and running W Mostly gregarious and ground-nesters W Important game and domestic birds
W Family Tetraonidae - grouse and ptarmigan Z 8 species in U.S. and none in MS
Ptarmigan Ruffed grouse
W Family Phasianidae - quails, partridge, pheasant, junglefowl, peafowl
Z 9 species in U.S. (some introduced: pheasant, partridge, chukar) and 1 in MS (northern bobwhite quail)
W Family Meleagrididae – turkeys
Z 2 species worldwide and 1 in MS Chukar
Junglefowl Gambel’s quail
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Z Order Gruiformes - cranes, rails, coots, gallinules
W Prairie and marsh dwellers
W Family Gruidae – cranes
Z 15 sp worldwide and 2 in U.S. (whooping and sandhill)
W Family Rallidae - rails, coots, and gallinules
Z 142 species worldwide and 9 in MS
Coot
Sora rail Whooping crane
Z Order Charadriiformes W Assortment of shore and sea birds with about 40 species in 8 families in MS (18 families worldwide) W Most strong fliers and often colonial W Includes oystercatchers, plovers, snipe, woodcock, avocets, stilts, gulls, terns, and skimmers
W Family Laridae - gulls and terns Piping plover
Oystercatcher Stilts
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Z Order Gaviiformes – loons
W Foot-propelled diving water birds with loud, haunting call
W Great swimmers that can dive up to 600 ft. but cannot walk and can only scoot on land
W Family Gaviidae - only family with 5 species worldwide (1 in MS - common loon)
Z Order Columbiformes
W Family Columbidae - pigeons and doves
Z 310 species worldwide and 4 in MS (rock and mourning dove common)
Z Order Psittaciformes - parrots and allies
W About 360 species and none in MS after Carolina parakeet went extinct in 1912 from overhunting
W Family Psittacidae - parrots and macaws (281 species)
Z Found in all tropics of the world and Australia Z Many kept as pets with 400,000 imported annually to the U.S.
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Mourning dove
Carolina parakeet
Z Order Cuculiformes - cuckoos, hoatzins, roadrunners
W Family Cuculidae - cuckoos, anis
Z 142 spp worldwide and 1 in MS - yellow-billed cuckoo
Cuckoo Ani Roadrunner
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Z Order Strigiformes – owls
W Nocturnal predators with forward facing eyes, large ear openings, and soft, fluffy plumage for silent flight
W Family Tytonidae - barn owls Z 11 species worldwide and 1 in MS
W Family Strigidae - all others Barn owl Z 135 species worldwide and 6 in MS
Great horned owl
Z Order Caprimulgiformes W Small bill with large mouth surrounded by insect-netting bristles W Twilight insect feeders that lay eggs directly on ground W Family Caprimulgidae
Z 77 species worldwide and 3 in MS (whip-poor-will, chuck-will’s-widow, and common nighthawk)
Chuck-will’s widow
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Z Order Apodiformes - swifts and hummingbirds
W Family Apodidae – swifts Z 83 species worldwide and 1 in MS (chimney swift) Z Short legs and small feet with very small, weak bill
W Family Trochilidae – hummingbirds Z 341 species worldwide and 1 in MS (ruby-throated)
Chimney swift
Ruby-throat
Z Order Piciformes – woodpeckers W 2 toes in front and 2 in rear with specialized stiff tail feathers
W Nests in cavities and has specialized bill for wood-boring
W Family Picidae
Z 204 species worldwide and 8 in MS Z From small downy woodpecker to large pileated woodpecker Z The red-cockaded woodpecker is highly protected and endangered Z The ivory-billed woodpecker was the largest and is now probably extinct
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Red-cockaded woodpecker
Yellow-shafted flicker
Z Order Passeriformes – almost every other bird W About 5,000 species (60% of known birds) of passerines W Considered songbirds and have a more highly developed syrinx (sound box) than other birds
W 21 families in MS including:
Z Flycatchers, larks, swallows, shrikes, waxwings, wrens, mockingbirds, thrushes, buntings, cardinals, tanagers, wood warblers, vireos, blackbirds, finches, crows, jays
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Morphology Z Integument (skin)
• Feathers – modified reptilian scales derived from the epidermis unique to birds
• For insulation and adapted for flight
• Epidermal scales – like those of most reptiles and are found around beaks and on legs
• Claws and beak also derived from epidermis
Z Feather characteristics
• Weight of feathers can be more than rest of the bird
• Structure
• Made of keratin – inert substance of microscopic filaments embedded in a protein matrix (a bit like fiberglass)
• Resistant to digestion by microbes and fungi
• Basic feather morphology: shaft, vein, barbs and barbules
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• Shaft – long central support that consists of an anchor portion (calamus or quill) and the portion that supports the vanes on either side called the rachis
• Vane – primary elements are branches of the rachis called barbs
• Each barb consists of a tapered support shaft called the ramus and further branches called barbules
• Barbs and barbules interlock and form a flexible surface that contours and protects the bird’s body
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Z Amount of cohesion among the barbs and barbules reflect function
• Feathers with tight arrangement of barbs can look like strips of plastic (neck feathers of roosters) which can act as courtship, protective, or waterproof structures
• Feathers with loose cohesion can act as insulating structures that trap air (down feathers of waterfowl)
Z 5 types:
1. Contour – forms outline of the body and include large flight feathers and overlying breast feathers; firm vane (feather part) and well developed rachis (shaft)
2. Semiplumes – help insulate the body and increase buoyancy
• Intermediate between down and contour • No firm vane but a defined rachis
3. Down – primarily for insulation
• Under and between contour feathers • Rachis not very evident and vane is fluffy plume
4. Bristles – found around nostrils where they filter air and around mouth where they aid in collecting insects
• Almost no vane, only a stiff rachis • Some have sensory function with corpuscles (pressure sensing cells) at their base
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5. Filoplumes – scattered over skin and can have decorative and/or sensory functions
• Hairlike feathers with no vane and a threadlike rachis • Long colorful peacock feathers are filoplumes
Z Feather Care
• Unlike bones and skin cells, feathers are “dead” and do not receive materials from the body after they grow to full size, so they would become brittle without daily preening
Most birds have a gland at the base of their tail, the uropygial or preen gland, that secretes a substance that prolongs the life of a feather
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• The substance is a rich oily mixture of waxes, fatty acids, fat, and water
• The waxy secretion does several things:
1. Preserve moistness and flexibility
2. Stop growth of undesirable fungi and bacteria
3. Discourage feather lice
4. And, in some birds, have a pungent odor to discourage mammalian predators
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Z Molting – feathers are replaced annually and usually within a short period of time
• Many small birds lose feathers in sequence and retain the ability to fly at all times
• Waterfowl lose many feathers at once and cannot fly for a period of time
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• If a feather is injured it cannot be repaired since it is a dead structure and the only way to repair is to replace it
• Follicle muscles and friction hold a feather in place and these muscles are controlled by the autonomic nervous system (birds cannot consciously lose feathers), and some birds if frightened will drop some feathers
ZBirds start life with a coat of natal down then juvenile “stiff” feathers push them out of the follicle
• In some birds (waterfowl), a second set of down will grow later in life from a different set of follicles
• Most birds molt after breeding, replacing colorful plumage with more cryptic coloration
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• Some birds may keep their feathers for 12 months but most molt twice a year
• You can sex and age many birds by looking at plumage coloration and wear
Color phases for adult Scarlet Tanagers
Z Pigment – solid granules of various colors
• Melanins – blacks, grays, buff, and browns
Found in all birds
Body produces the granules regardless of diet
Melanins associated with keratin give strength to feathers and make them more resistant to wear
In desert species, they protects feathers from sand abrasion
Can help dry feathers as granules absorb excess moisture then easily evaporate it away with radiant heat
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• Carotenoids – intense reds and yellows
Found in many birds
Derived from the diet so birds must eat the chemicals responsible for the color
Distribution of pigment within the feather can regulate intensity of the color: birds with red granules in both barbs and barbules are bright red, those with granules in barbs only can be pink (mix of red and white)
Flamingos eat invertebrates with carotenoids, mainly small shrimp, to produce pink-red colors
• Porphyrins – reds, browns, and greens
Relatively rare and unstable pigments producing intense colors
Produced by the body
Usually only found in new feathers because UV- radiation eventually breaks down the granule
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W Most metallic blues and greens and iridescence are produced by refractive properties of the feather vane (some colors in parrots, bluebirds, hummingbirds)
Z Skeleton
• Specialized for lightness and strength so many bones have paper-thin walls
• Many contain no marrow but have support struts inside
• The skull is reptile-like but bones are thin and fused
• A sclerotic ring of 10 to 18 overlapping bones around the eye orbit reinforces the proportionately huge eyeball
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• The beak is used to:
1. Obtain food 2. Preen feathers 3. Build nests 4. Defense
• Both mandibles are very mobile and the shape and size of the beak has evolved to suit the life history of each species
Bird vertebrae (other than neck) are fused to help keep the trunk of the body stiff during flight.
A bird's pelvic girdle and the lumbar, sacral, and a few caudal vertebrae are fused into a single, solid structure called the synsacrum.
• Cervical, thoracic, lumbar, sacral, and caudal vertebrae are present and most sections are fused as one unit for increased rigidness
• Pectoral and pelvic girdles are highly fused
• All birds have claws on their feet and some have them on 1 or 2 digits of the wing (ostriches, geese, some swifts)
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Z Ostriches are the only birds with only 2 toes the rest have 3 or 4 functional toes
• As with the beak, feet shape and function are highly variable depending on the life history of the bird
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• Birds have fewer epidermal glands than any other group of vertebrates and the only one that is well developed is the uropygial gland near the cloaca
• The sternum usually has a large keel (carina) to anchor flight muscles and size of the keel is related to the bird’s flight ability (some flightless birds do not have one)
Z Muscles • Most metamerism (muscles arranged as myomeres) are gone • Muscles are arranged in bundles not segments as in more primitive animals
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ZTypes:
• Red – fibers are small in diameter and have a rich blood supply
Have myoglobin along with hemoglobin for increased oxygen storage
For sustained activity during prolonged flights
Birds that primarily fly (most) have red muscle in the breast
• White – designed for short bursts of intense activity
Birds that primarily walk (turkey, chickens) and only fly occasionally have white muscle in the breast
They must have a lot of power available for quick takeoff
Gallinaceous birds (chickens, quail) have white muscles in the breast and red in the hind quarters
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• The pectoral (breast) muscle of flying birds is proportionately the largest muscle of any tetrapod and can account for 25% of body mass (most 15-20%)
• Large flight muscles create enormous amounts of heat during flight and metabolism increases 7 to 13 times the resting rate (some heat is retained for the body but most is lost to evaporative cooling)
• Hummingbirds flap their wings from 80 to 100 times/second and their heartbeat rises from 500 beats/min resting to 1300 beats/min in flight
Z Wing shape
• Longer, more pointed wings are typical of open-country birds
Good for high speeds (sea birds, falcon, killdeer)
• Shorter, more rounded wings are typical of birds living in dense vegetation
Good for quick maneuvers (forest hawks, quail, wren)
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Z Flightless birds – 3 paths
1. Ratites – ostrich, emu, and rhea are large and can protect themselves from predators by defense (kicks) or running
2. Island birds – many islands were free of predators before man and flight was not necessary
Z Food could be obtained easily by walking and grazing or eating fruit
Z Dodo, some geese, parrots, kiwi
3. Diving birds – both foot- and wing-propelled divers may lose flight ability
Z Penguins, some grebes, some cormorants
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Mechanics of Bird Flight
Z Several components of flight to consider:
• Taking off • Maneuvering • Stabilizing positions • Landing
Z Flight is the most economical form of locomotion over long distances
• A 10-gram bird in flight expends <1% of the total energy required by a 10-gram mouse to run the same distance
• But, there is a high short-term energy cost to get aloft
Z There are four physical forces that must be in balance for successful flight:
1. Weight – the pull of gravity on the mass of the bird
2. Lift – upward air pressure force that counters the downward force of gravity
3. Drag – the collective slowing influence of turbulence and friction
4. Thrust – the forward force that counters drag
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Z In airplanes, the wings provide lift and the engines provide thrust, but in birds the wings do both
Z Bird wings function as an airfoil just like airplane wings
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Z Increased airflow (forward speed or wind) and larger surfaces (wing area) produce more lift as air rushes over the top and is pushed downward
Z To slow themselves, birds increase the angle of attack of the leading wing edge and air stops flowing over the top and the bird stalls (as in airplanes)
• The alula (a small winglet that separates from the main wing) helps sustain lift when birds are at low speeds just before landing
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Z To produce thrust, a bird uses downbeats of the wing to overcome drag or friction
• Birds fly through air like fish swim through water, although air presents much less resistance
• A wing’s downbeat works much like a paddle pushing water backward so a canoe will move forward
• The energy cost of flying is:
Least at intermediate speeds
Greatest at low (little lift) and high (increased friction) speeds
• Hummingbirds hover in front of flowers to extract energy rich nectar and fly fast to beat competitors to more flowers (both energetically expensive)
One of the few examples of birds not utilizing intermediate speeds to conserve energy
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Z Migrating birds will fly faster than their intermediate speed to cover greater distance with same amount of fuel
• The added momentum with increased speed gives more range over long distances
• Large migrating birds with relatively small wings fly in a “vee” formation to reduce drag and save energy
Cormorants Snow Goose
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Types of flight
Z Soaring/gliding
• Usually done by large birds (vultures, hawks) and requires little energy
• But in still air, a gliding bird will slowly sink so they take advantage of rising air from two sources
1. Thermal soaring – columns of warm air that rise when the ground is heated by the sun
Soaring birds sink at about 1-2 meters/second but thermals rise at about 4 meters/second so they can circle upward
Some use this technique to search for food (vultures) or for migration (hawks)
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2. Slope soaring – air directed upward when a wind hits a mountain ridge or an ocean wave
Migrating hawks can soar along ridges
Large sea birds (gulls, albatross) can glide along waves with little effort
Z Flapping flight
• Hummingbirds fly like most birds but flap their wings at extremely fast rates
They have the highest rates of oxygen consumption and muscle power output of all vertebrates while hovering
Their flight resembles a combination of helicopter and airplane flight, much like the Air Force’s Osprey
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• The wings rotate about a horizontal axis to produce combinations of lift and thrust
• They can hover, move up and down, and forward and backward (they change wing direction and push air forward so they move back)
• They have evolved special articulations of arm bones and ligaments to accomplish this (most birds do not have these adaptations)
• Once a hummingbird’s wingbeat rate reaches its natural oscillating frequency, it only has to fire or flex its wing muscles once for every 4 beats, sort of like a child on a swing that needs a push at times to keep swinging
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The typical wing beat pattern of most birds, including hummingbirds, in normal flight
Z No aircraft can approach a bird’s acrobatic maneuverability
• They have intricate control of each wing and rarely crash during takeoff, aerial maneuvers, and landings
• Asymmetrical wing control action enables birds to steer, turn, and twist in flight like no airplane can
Statistic Plane type Bird species Speed (body Supersonic SR-1 – 32 Pigeon – 75 length/second) Starling – 120 Swift – 140 Roll rate A-4 Skyhawk - 720 Swallow – 5000 G force allowed General aircraft – 4-5 Most species – 10-14 Some military craft – 8-10
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Z Intermediate flight
• Most birds alternate between regular bouts of flapping with short periods of non-flapping flight
1. Many hawks and vultures flap several times and then glide for a while (flap gliding)
2. Woodpeckers and jays rise and fall in quick sequences as they alternate (flap bounding)
• All modes of flight we see among species are an effort to reduce power costs and body size will determine what is most efficient
• Flap gliding is favored in large birds and flap bounding in medium-small birds
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Respiratory System Z The larynx is not the sound-producing organ as it is in mammals, it only modifies sounds originating from the syrinx
• The syrinx is the unique voice box of birds and is an enlargement of the trachea
• The trachea of some species (trumpeter swan) is looped and coiled to produce a deep, resonating sound
ZBirds have no muscular diaphragm as in mammals but a thin diaphragm does separate the lungs from the rest of the body cavity and aids a bit in breathing
• Most movement for breathing is done by muscles around the ribs that move the ribs and sternum to force air in an out
• Birds may have 7 to 12 air sacs that can fill up to 80% of the body cavity (they aid the lungs but are not for gas exchange)
• Air goes from trachea, posterior air sacs, lungs, anterior air sacs, then out trachea in a series of steps (see next figure)
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• Parabronchi are the gas exchange canals of birds, not alveoli (close ended sacs of mammals) • Only fresh air passes through the lungs and parabronchi for a very efficient, unidirectional respiration system • Flight is highly energetic and muscles requires a lot of oxygen during flight and if birds did not have this super- efficient, voluminous gas exchange system, flight would not be possible
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Digestive System Z No living birds have teeth
• Tongues are non-muscular and contain few taste buds but have some tactile sensors to examine food items
• Birds that probe the ground for food may have well developed sensors on the tongue to feel for food (kiwi, snipe, woodcock)
• Oral glands (mucous, saliva) are much more numerous than in reptiles or amphibians
Some use saliva to help construct nests (swifts) and swiftlets make their nest entirely from saliva
Z The esophagus takes food from mouth to stomach
• The lower part of the esophagus in most birds has a crop (a sac for food storage)
Swiftlet nests are main ingredient of bird nest soup in Indonesia
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• With a crop, food can be eaten and stored quickly allowing the bird to retreat to a safe spot (high roost) and slowly digest it
• Primarily grain eating birds have large crops but some birds that bring back food for young have them also
• The stomach is divided into 2 parts
Proventriculus – 1st part is soft and secretes gastric juices (food is emulsified)
Gizzard – 2nd part is muscular and grinds food with the aid of grit and takes on the role of teeth for birds
Z Birds display a wide variety of feeding habits and stomachs are modified slightly to accommodate different digestion needs: meat (hawk), grain (chicken), berries (waxwing), grazers (geese), fish (cormorant)
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Cardiovascular System
Z Birds have 4 well-developed heart chambers so no mixing of oxygenated and de-oxygenated blood occurs
Z Larger birds have relatively smaller, slower beating hearts (turkey – 100 bpm, chicken – 300 bpm, sparrow – 500 bpm)
Z Rete mirabile (retia mirabilia) – countercurrent heat exchange system to reduce heat lost by the legs
• Birds in cold climates or those that stand in water a lot must have a way to reduce heat lost by the legs
• At the junction where legs attach to the body, this net of vessels transfers heat from vessels with blood leaving the body/heart (arteries) to vessels entering the body (veins) so little heat goes to the legs and most is retained in the body
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Water Balance and the Urogenital System
Z Birds have relatively high body temperatures because of their unusually high levels of activity
• As with mammals, birds must use evaporative cooling to maintain their core body temperature at the proper level
They must be very efficient at obtaining water from every available source so they do not dehydrate
Many birds are able to get enough water from their food
Nectar, fruit, meat, and insect-eating birds need little to no water from their environment but in most cases, seed-eaters must drink water
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• Some birds get most of their water from metabolic processes
Metabolic water is produced as a by-product of the oxidation of organic compounds with hydrogen
Example: the metabolism of 1 gram of fat yields energy plus 1.07 grams of water
A zebra finche can survive on a diet of dried seeds (containing <10% water) and metabolic water alone
• One advantage of not drinking water is safety, especially in arid areas where many predators sit and wait near water holes
Excretion of Nitrogenous Waste
Z The metabolism of proteins for maintenance of tissues produces nitrogenous products that are toxic if they accumulate
• The kidneys are the main organ that extracts this waste from the blood
• Aquatic vertebrates (fish, some amphibians) aren’t concerned with water conservation so they excrete the
simplest type of waste NH3 (ammonia), which is water soluble and very toxic
• To conserve water, mammals excrete urea, a more
complex molecule (NH2x2)
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Requires less water to expel compared with ammonia
Not as toxic and can be stored (bladder) or accumulate in the bloodstream for short periods
WBirds need to be as light as possible so they excrete uric acid (NHx4) which can be stored as a semi-solid suspension that requires very little water to expel
• Birds need only 0.5-1.0 mm of water to excrete 370 ml of uric acid
• Mammals need 20 mm of water to excrete the same amount of nitrogenous waste or 20-40 X more water
• Many reptiles also excrete uric acid to conserve water in arid environments
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Ammonia Urea
Uric acid
Z Birds that live depend on oceans for food and water must deal with excess salt in their system
• Seawater is 3% salt and body fluids of birds are 1% salt
• Birds rely on nasal salt glands to extract excess salt because their kidneys, which perform this function for mammals, aren’t very efficient at it
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• Salt glands are formed from infoldings of the cellular lining of the nares
The infoldings extract salt from a set of capillaries and direct it toward a central canal that directs it out the nose and then it drips off the end of the beak
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Nervous System Z The bird brain
• Bird brains are 6-11 X as large as those of similar sized reptiles
• The hippocampus (a region of the forebrain) of birds is highly developed and allows them to have extraordinary spatial memory
Seed-caching birds are more enlarged allowing them to find thousands of seeds during the winter that they cached during the summer and fall
This also helps in finding remote wintering grounds and nest and foraging sites
Z Vision
• Birds use vision more than any other sense to process details about their environment
• They rely on vision to:
Search for food
Detect predators at great distance
Engage in complex, colorful courtship displays
• Passerines and raptors have the best sight and can resolve details at 2.5-3 X the distance that humans can
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Z In some species, eyes account for 15% of head mass, and the eyes of eagles and owls are the same size as in humans
Z Most birds do not have very good binocular vision (can’t see an object with both eyes at the same time)
• They bob their heads quickly to get several different angles of vision with one eye to develop image depth
• Owls have the greatest field of binocular vision and woodcocks have the least but can see almost 360° around
Woodcock
Visual fields of birds have been categorized as:
Type 1 (a). Large cyclopean area; largely monocular vision (e.g. Rock Pigeon, Starling, and Cattle Egret)
Type 2 (b). Very large cyclopean area; small binocular fields in front and back (e.g. Eurasian Woodcock)
Type 3 (c). Larger frontal area with large binocular field (e.g. Tawny Owl).
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Z Birds see the same spectrum of light we do plus wavelengths into the ultraviolet (UV) spectra
• The color in their feathers relays much more information to them than it does to us
This guides mate choice, dominance relations, and reproductive success
Some birds also choose food based on UV light reflectance which guides them to the most nutritious foods (flower nectar, berries)
Z Detection of magnetic fields
• Birds respond (orient themselves) to weak and strong magnetic fields like the Earth’s
• Magnetite crystals are present in bird’s heads in the cranial nerve system and the thin bones of eye orbits
• This helps them greatly on long journeys such as migration (more in later lectures)
• The method by which they detect strength and orientation of fields is still unknown
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Z Hearing
• Sounds assist birds with territorial defense, mate choice, and navigation to various degrees depending on species
• Most birds do not have extraordinary hearing and humans can hear fainter sounds than many species
• Some can detect low frequency sounds outside the range of human hearing (pigeons, chickens)
• Owls have exceptional hearing among birds
They can locate prey by sound in complete darkness
• It can locate sounds to within 1° in both the vertical and horizontal plane (humans can locate sounds about as well in the horizontal plane but 1/3 as well in the vertical plane)
• The ears are asymmetrical and throw off arrival of sound by milliseconds which pinpoints sound vertically
• The left ruff faces downward and the right ruff faces upward and this pinpoints sound horizontally
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• Some species (swiftlets, nightjars) use echolocation to navigate in darkness of caves or at night
They still are using frequencies within the hearing range of humans so it’s not as functional as what is seen in bats which use ultra-sound (at best only 1/10 as functional)
Z Chemical senses: taste and smell
• Birds can taste but not very well (almost negligible):
Humans – 10,000 taste buds Chicken – 24 taste buds Pigeon – 37 taste buds
• Most birds can smell to some degree but the range of smells is limited and is usually related to some important aspect of survival or reproduction
Grazing birds (geese) reject some food plants that are toxic
Starlings select nest material with smell (some plants reduce parasites in the nest)
African honeyguides can find beehives at a good distance
Male mallards must smell a female’s breeding odors in order to stimulate his courtship behavior
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• Some birds have large olfactory bulbs in their brain and rely on smell much more than others
Vultures can locate carrion at a great distance
Kiwis select food items underground and in darkness
Many tube-nosed sea birds (petrels) find zooplankton, mostly krill, on the open sea
Storm petrel
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Visual Communication
Z Birds communicate their intentions to other birds with vocalizations and displays
• Most of the time, calls and displays are used in conjunction and have evolved together
• Displays can communicate:
Territorial defense Attraction to mates Maintenance of social structure for colonial birds
Z Many species have striking color differences between the sexes (sexual dimorphism) and between seasons
Z Cryptic coloration (camouflage) – the most important role of plumage is to conceal the bird from predators • Ptarmigan live in the tundra and taiga and change from white plumage in the winter to patterned brown in the summer that matches lichen covered rocks • American bitterns will stand still and point its bill skyward, and along with its plumage it blends in well with marsh reeds
Bittern Ptarmigan in spring
Ptarmigan in winter
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Z Countershading (dark on top and light on the bottom) works well for birds living in open country • Killdeer and shore birds are a good example
The overall outline is disguised as predators focus on either the top or bottom and can’t identify the bird
Killdeer plumage further disrupts its outline with bold bands around the neck
Killdeer
Dunlin
Z For many birds, the advantage of calling attention to oneself takes precedence over the need for concealment during the breeding season
• Male cardinals are a solid color and along with the crest, stand out in contrast to surroundings
Males remain brightly colored during the winter to retain dominant status (the brighter the color, the more dominant they are)
Cardinals do not migrate so they retain territory all year
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• Colorful wing patches of male ducks
• Dark triangular shapes under the bill of some birds call attention to movements of the bill (hooded warblers)
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Z Species recognition
• All species will have unique breeding plumage
Even sea birds that seem to have either uniform mottled brown or white-gray-black plumage will differ in beak, leg, and/or eye color during the breeding season
They must have their feather color for hunting and concealment because they are in open habitat
Caspian tern Royal tern
• Young chicks imprint heavily on parental plumage and this experience stays with the bird when it’s ready to breed
Color patterns and intensity get reinforced with every generation so they are as bright as possible until some limitation (need for concealment for hunting or survival) brings the color pattern to a “fittest” state
If birds are raised by another species, then later when time to breed they will choose the foster species, but this experiment has its limits
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Z Studies show that many morphological traits are affected by parasite load so females can distinguish which males are most fit:
• Strength of irridescence (bowerbirds) • UV intensity (bluebirds) • Comb size (junglefowl)
Z Evolution of Displays
• We can trace evolution of closely related species by mapping courtship moves
• Manakins have very elaborate displays
They do a variety of motions and sounds: whirls, jumps, castanet-like click with wing, struts up and down limbs
One researcher mapped displays of 19 species and also shape of several body parts and both methods grouped the species similarly (some were closely related and others more distantly)
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Club-winged manakins can make a violin-like sound with its modified wing feathers
• Many ritual displays evolved from common motions that have been enhanced to ceremonial status
Quail and chickens go through a feeding ceremony, but quail actually give the female food then they mate and chickens just go through pecking motions then mate
Peacocks simply nod their head in a feeding motion once or twice then mate
Other common motions that are used in displays include: beak wiping, feather preening, drinking, leaping in the air to begin flight, and pecking
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These displays are somewhat innate and also learned so if a male never gets it right, then he doesn’t mate and those genes die with him
• Male bower birds have traded bower building for elaborate, colorful plumage
The male builds a structure (a bower) from common forest items and the female inspects each and picks a male in the same way other species use plumage
As with plumage, bowers are species specific and must be done exactly the same as recent generations
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Bird Vocalizations
Z Animals use visual, acoustical (vocal), tactile, chemical, and electrical signals – birds use visual and vocal
• Foremost, both visual and vocal signals are species specific so other birds know what to look and listen for
• Next, vocalizations identify individual identity within that species – gender, social status, pair bond, or family relationships
Z The syrinx, which controls the sound, can produce incredibly complex calls and can even produce 2 independent songs simultaneously
Z Song – long vocal displays of males with specific, repeated patterns often pleasing to the human ear (these are what identify most species to bird watchers and biologists)
Z Call – a short, simple vocalization that can be given by either sex (distress, flight, warning, feeding, nest, and flock calls)
Z The above categories are completely categorized by human perception (i.e., how much information can we glean from the sound)
• But, there are 2 functionally real categories of bird vocalizations: whistles and harmonics
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Z Whistled songs
• Lack harmonic content
• The oscillogram shows one sinusoidal wave form that varies in pitch by varying amount of escaping air
• Differences among whistled vocals are due to frequency of oscillations (how often the air compression changes/unit time)
Low pitch sounds (bass) have low numbers of oscillations and high pitch sounds have many oscillations
• The sonogram shows amount of energy put into the call with respect to time
Z Harmonic songs
• Have overtones (tones produced at different frequencies and different levels of energy or amplitude)
• One harmonic will be dominant (more amplitude)
• Harmonic songs can be complex because of the added dimension of layers
• Many times harmonic songs are of short duration
Z Differences in physical structure make whistled or harmonic vocals more advantageous depending on the situation
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• Harmonics give a lot of information on direction and distance because of all of the frequencies in one call
Harmonic sounds may be used when the bird wants to be located (mate attraction)
ZWhistles are used when birds want to relay information but at the same time do not want to be seen (alarm call)
ZCalls of high frequency do not travel far through dense structure without distortion so birds of dense forests use low frequency sounds
• Harmonic calls are also disrupted by dense structure so birds of dense forests use fewer harmonic calls
• Forest birds tend to use simple vocals of low frequency
• Open-habitat birds tend to use complex, high frequency calls
Z Details of song pitch, phrase structure, syntax, and composition serve as individual signatures that enable birds to identify offspring, parents, mates, and neighbors
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Z The syrinx has two independent halves that can produce different, complex songs simultaneously • We cannot reproduce this effect with musical instruments (wind instruments) or the human voice
• Birds do this by a complex system of movements of the trachea (length change), larynx (constriction), and beak (flare)
Z Bird vocals are inherited (genetics), learned, or invented
• Brood parasites (cuckoos, cowbirds) must have inherited vocals as do chickens and doves
• The eastern meadowlark inherits the call notes but learns the song from other meadowlarks
• Vocal learning is usually restricted to early development, within the first 6-12 months of life
When males reach the first breeding season and testosterone levels rise for the first time, they usually cannot learn songs afterward
Tests show that castrated males of many species can learn songs for much longer
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Z Most males improve their songs over time and attract more females as they master the song
• The sonogram of an adult tutor canary (above) and that of a juvenile at 12 months (below).
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Breeding Systems
Z From an evolutionary stand point, the only thing that matters in the end is passing genes on to the next generation
• There are 2 ways to do this:
1. Directly producing young with your own genes
2. Indirectly by helping relatives to raise young that have some of your genes
• DNA analysis shows that extra-pair copulation occurs frequently, even in species we used to think were monogamous
• A big reason this is advantageous is to increase genetic diversity within a brood
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Z Parents make choices or tradeoffs between taking care of the young or abandoning them to find more mates
• In some cases (tree swallows), the young of one male are killed by another so he can start his own brood
• This usually happens when quality nest sites are scarce and males take over the nests of others
Z With each mating strategy, there is always an underlying factor that increases survivorship of the parent, the young, or both
• For most species, it is to reduce risk of predation or risk of starvation for chicks
Z Monogamy – neither sex has a chance to monopolize additional partners (one male and one female)
• Shared parental care maximizes reproductive success
• The majority of bird species
Z Polygamy – any mating system with multiple mates of the opposite sex
• Only 3% of bird species are polygamous
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• Polygyny – males have 2 or more females
About 2% of bird species (14 of 278 songbird species in North America)
Male breeding success is more variable than females
• Males may control access to females in several ways:
1. Control some critical resource
Called resource defense polygyny
Occurs more in tropical species that feed on fruit or nectar because males do not need to help feed young when food is so abundant
Some humming birds control access to flowers and nectar
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2. In gregarious species, males may directly control a group of females and defend them
3. Males may compete for dominance with other males by direct fighting or display (or both) and females choose them
Male prairie chickens display on a patch of ground, or lek, and display for females who gather in large groups around successful males
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• Polyandry – females have 2 or more males
Each male tends to a clutch of eggs
Female breeding success is more variable than males
<1% of bird species
Mostly found in 2 Orders of birds: Gruiformes (rails) and Charadriiformes (some snipes, sandpipers, jacanas)
Females have higher levels of testosterone which increases aggression and inhibit incubation while males have high levels of prolactin which causes more parental behavior
• Polygynandry – several females and several males form a communal breeding unit
Males defend territories and provide parental care in proportion to how confident they are of paternity
All ratites (emus, etc.) and few songbirds
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Male ratites have territories and females will visit several and deposit eggs in each nest
Z Cooperative breeding
• Some bird species raise young in family groups with “helpers”
• This seems like altruistic behavior where individuals place the good of their population or species above their own well-being
• There are several factors that contribute to this behavior and can explain the individual benefits
1. Helpers may directly enhance their reproduction by delaying their own dispersal
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2. Helpers may get indirect benefits by helping in the production of genetic relatives (full or half siblings)
Called kin selection
This is similar to what is seen in social insects where sterile workers help their mother produce and raise sisters
3. Helpers may also get indirect benefits by getting help in return when they have a brood of their own
Called reciprocal altruism
Works well as long as there is no “cheating” by some individuals
• We know of about 400 species with some level of cooperative breeding (do all individuals of a species practice it or a small portion?)
• A good example is the Florida scrub jay
About half of breeding pairs have helpers
The unit consists of a breeding pair with up to 6 helpers that may stay around for 1-7 years
Pairs with helpers fledge more young per year
The main benefit is better defense against snakes, the primary nest predator of the species
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Nests and Incubation
Z No birds have live young, so all have to ensure their eggs are hatched
• Eggs, hatchlings, and attending adults are all vulnerable to a host of predators
• Also, the entire process is a large investment of time and energy for the parents
• Birds have evolved many nest types and social structures to cope with the hazards
Z Nest architecture
• Range from simple depressions in the ground to elaborate baglike structures
• Examples:
Pebble nests of killdeer Sandy scrape of plovers Mud nests of cliff swallows Cavity nest in cactus of gila woodpecker 2 ton nest of bald eagle used for 30 years Woven nests with long entrance of weaverbirds
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Z Nest materials may be selected to decrease ectoparasites in the nest
• Hole nesters use green vegetation more than open nesters and this may help combat parasites
• Starlings select certain plants, nettle and yarrow, by odor which contain chemicals that inhibit growth of bacteria and some arthropod eggs (mites)
• Birds may use many other things available in their habitat for building nests including: snake skins, spider web, feathers, animal hair, mud pellets, and rocks
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Z Predation on nests severely reduces breeding success
• For many species, it is this life history event that determines population size the following year
• In some cases, more chicks are eaten by predators than fledge (mature to the point they can leave the nest)
• Evolution of clutch size and nest placement and shape many times is determined by predation pressure over time
Z Nests can be protected 3 ways:
• Invisibility – incubating whip-poor-wills, speckled shorebird eggs, and lichen nests of hummingbirds are about completely invisible
• Inaccessibility – some seabirds nest on sheer cliffs, some swifts nest in deep caves or behind waterfalls, many grebes build nests of floating vegetation
• Impregnability – pensile (hanging) nests make it difficult for snakes to enter nests
Some starlings and sparrows nest on the fringe of imperial eagle nests A plover of Africa nests beside nesting crocodiles
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Z Covered or cavity nesting is always safer than open nests of any type
• About half of the avian orders nest in cavities or holes
• Woodpeckers chisel their own cavities and competition is intense among other birds for an abandoned woodpecker cavity
• Availability of nest holes limits the population size of some species
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Z Tree nests are safer than ground nests, mostly because they’re protected from many mammalian predators
• Mourning dove can nest on the ground or in trees and tree nests on average are more successful
• Tooth-billed pigeons once nested on the ground on Samoa, but shifted to tree nesting after cats were introduced
Z Parents may protect nests in a variety of ways:
• Parents with cryptic coloration may cover nests until the last moment of detection
• Common eiders of the arctic will stay put until the last moment then flush and defecate noxious fluid on eggs
• Some directly attack predators: mockingbird, large birds of prey, eastern kingbird
• Distraction displays: usually injury-flight or rodent-run (crouching and appearing rodent-like to appeal to predator instincts)
• Many parents land away from nests and sneak back through grass or bushes
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Z Colonial nesting
• About 13% of bird species (most seabirds) are colonial nesters
• Evolves in 2 environmental conditions:
1. Shortage of safe nesting sites
2. Abundant and sometimes unpredictable food that is a distance from safe nest sites
• Advantages:
Safer in colonies inaccessible to predators
Detect predators more quickly
More easily drive predators away
Synchronized nesting produces more chicks at one time than local predators can eat
When food is off-site, others can watch your nest
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• Disadvantages:
Must be a rich, clumped food source nearby
¾ Seabirds nesting on Peruvian coasts depend on enormous schools of fish in the nutrient rich Humboldt Current and during El Nino years the current moves far offshore and populations crash
Increased competition for nest sites
¾ Nests are safer in the center of the colony so birds compete for those locations
¾ As a result, colonies are super-dense even when available space is abundant
Stealing of nest materials
Increased competition for mates
Increased spread of disease (parasites may lower survivorship by 50% in large colonies compared to small ones)
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Z How do birds know how to build nests?
• Most birds build nests so specific we can identify the builder to at least genus
• The ability seems to be much like male song capability, some have the innate ability (genetic) and others must learn or a mixture
• Raptors imprint on natal nests and will choose a similar site later (mostly learned behavior)
• Many weaverbirds of Africa can build intricate nests when hatched and raised in isolation in captivity
• Many birds start with some ability and improve over time
Z Incubation
• No bird incubates eggs internally and eggs must be kept within a narrow developmental tolerance range of temperatures
• Consequently, parents are constrained to rigorous incubation patterns
• Incubation behavior is mediated by the hormone prolactin, which is elevated in the bloodstream during the incubation period
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• Testosterone inhibits incubation behavior and in species where only one gender does most of the incubation, prolactin increases in that gender but not the other
• Most birds wait until all eggs are laid until they begin incubation, that way they all hatch at the same time
• Birds transfer heat to eggs through brood patches
Bare sections of skin on the belly and breast
Most birds lose sections of feathers to form the patch and some use normally bare areas (doves)
Blood vessels proliferate in this area at this time to increase body heat transfer capability
We check for breeding condition by looking for brood patches
Some birds (penguins and some shorebirds) incubate eggs on their well-vascularized webbed feet
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• Range of temperatures:
Optimal is 37-38 °C (100.5 F)
Critical is 35-40.5 C
Above the critical range is quickly lethal, below and development slows or stops
• For most birds, it’s a challenge to keep eggs warm enough
• For some who nest in deserts or on hot beaches, they must keep eggs cool enough and must constantly shade the eggs or use water for evaporative cooling
• Incubation at normal temps consumes about 16-25% of a bird’s daily energy
Foraging time is limited, so birds fast (penguins) or depend on their mate for food (hornbill)
Some die of starvation or abandon their nest if their reserves aren’t adequate
• Incubation periods – time required by embryos for development given proper attention
Can be as short as 10 days for woodpeckers, cuckoos, and small songbirds
80-90 days in albatrosses and kiwis
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• Incubation periods tend to reflect longetivity of the adult birds and chance of predation for that species
Those that nest in holes have longer incubation periods because with more protection they can afford to incubate longer
• Incubation ends when the eggs hatch and birds then enter another stressful time, rearing young
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Development of Young Birds
Z Birds hatch at 1 of 2 levels of maturity
• Precocial – hatch out covered with down, legs well developed, eyes open and alert, and can soon feed itself
Young of the Lesser Golden Plover can leave the nest within 2 hours of hatching
Most are ground-nesting species that will be good runners or swimmers and feed either on the ground or in the water
Ducks, shorebirds, quail, chickens, grebes, rails
• Altricial – born naked or almost, usually blind, and too weak to support itself on its legs
The only thing it can do for itself is hold up its head unsteadily and gape for food
Parents supply all food until the young are near adult size
Young stay confined to nest for weeks in most cases
Herons, hawks, owls, passerines
• These are broad categories and there are some intermediate cases
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Z Egg types usually indicate what type of young will hatch from them
• Altricial birds lay small eggs with low yolk content so smaller energy demands are put on the female during egg production (energy is expended when rearing helpless young)
• Precocial birds lay heavier eggs with a larger yolk and females benefit when relatively independent chicks are born that can feed themselves
In one extreme case of precocial hatching, the megapodes of Australia, or incubator birds, bury their eggs in mounds much like crocodilians and young hatch then dig to the surface and are capable of flight and independent life.
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Z Altricial birds do not have well-developed nervous systems but their organs of metabolism (stomach, liver, kidneys, intestines) are enlarged in proportion to body size
• They are able to assimilate food at a rate unknown in other vertebrate groups (they grow fast)
• A cuckoo weighs 2 grams at hatching but will grow to 100 grams in 3 weeks (50 X its original weight)
Energy devoted to growth (G) and maintenance (M) added together is equal to the total metabolic rate (T).
Z After hatching, precocial young are led by the female to a place to feed and hide and the male usually has little to do with rearing the young
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Z After hatching, altricial young must be dried and sheltered in the nest and the task of feeding is usually shared by both parents
Z Nest or brood parasites (cowbirds and cuckoos) leave the eggs and young for parents of other species to care for
• Cowbirds can lay up to 40 eggs in other species’ nests in one season (up to 100 species are known victims)
• The female waits and watches other birds leaving nests then she deposits 1 or 2 eggs at dawn when the other female has started laying eggs and is out foraging
• Sometimes the host will notice the different egg and eject it
• The newly hatched cowbirds usually outgrow and out- compete for food other species’ young
• This process leaves the adult cowbirds free to follow herds (in the past bison but now domesticated cattle and horses) in search of food, mostly insects, that grazing animals kick up
• Most species are not adversely affected (on a population level) by low rates of nest parasitism, although 2 species of Vireo and Kirtland’s Warbler must be protected from cowbirds if they are to persist
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1 cowbird egg in bluebird nest Brown-headed cowbird chick
Reed Warbler parent feeding young cuckoo much larger than itself
Z In nearly all species, no matter what the adults eat (fruit, insects, grain, meat), the young are fed a protein-rich diet from day 1 then the amount of protein may be reduced as the chicks grow • House Sparrow adults eat about 3% animal matter and 97% vegetable but chicks are fed 68% animal matter and 32% vegetable
• A protein-rich diet helps muscles and feathers grow rapidly
• Some chicks are fed small bones or snail shells for more calcium and increased bone growth
• Chicks of many species remember food types they were fed when young, and when they have young of their own, they feed them the altered diet
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Z Feeding methods vary among species:
• Gallinaceous (chickens) birds lead their precocial young to food and point out palatable items
• Most species with altricial young simply bring a food item to the nest and place it in the chicks gaping mouth (passerines, woodpeckers)
Z Some parents swallow food and regurgitate it at the nest; this way they can carry more food and their digestive juices have softened it (gulls, storks, herons)
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• Pigeons and doves regurgitate “pigeon’s milk”, a creamy substance similar to rabbit’s milk
Both pigeon and mammal milk is produced when fatty cells are shed in the crop or mammary gland and production in both is controlled by prolactin
Birds of prey will bring dead animals to the nest and tear off pieces for chicks and later they will stop tearing pieces and let the chicks dismember the animal
Z Adult birds have a strong instinct to feed young
• The instinct is only present when chicks are hatched
• Sometimes, an adult will not fully go into feeding mode or another instinct will supersede it
Some parents will not start feeding young until several days after young hatch
Some migratory species will get the urge to migrate before the young are fledged (they die)
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• This Cardinal fed worms to goldfish in a small pool for several days after it lost its young
The Cardinal probably came to the edge of the pool to drink and the goldfish were used to being handfed
The open mouths of the fish triggered the feeding response in the bird
Z The most powerful stimuli to feed young in most species are the feeding calls of the chicks
• Parents with all of their chicks hidden except for one (they can still hear the other chicks), will stuff the one chick with over 2 X the necessary food and still try to feed it more
• When dove parents are made deaf they will not feed young enough, and deaf turkey parents will kill their chicks because they think they are nest predators
Z The nest must be kept clean during brood rearing
• The nest can’t become a breeding ground for insects so only eggs and chicks are kept in the nest
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• Feces of chicks can’t be dropped below the nest because predators will easily detect the location
• Parents carry fecal sacs (enveloped in a tough mucous membrane) away from the nests
• Some eat the sacs for a couple of days, then start carrying the sacs off as more feces are produced by the growing young
Z Duration of nestling period (altricial young)
• Larger species have longer nestling periods
• Open nesters have shorter times than cavity nesters
In the U.S., 11 species of open nesters averaged 11.0 days in the nest while 10 species of cavity nesters averaged 18.8 days
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Annual Cycles
Z Permanent residents have 3 concerns: breed, molt, and survive to the next breeding season
• Breed, nest, and rear young when food resources are plentiful and living is easy
• Molt soon after for fresh feathers when resources may still be available
• When the difficult season arrives, the bird has fresh feathers (of cryptic color) and only has to support itself
• In tropical areas it’s usually dry vs. wet season, in temperate to polar regions it’s warm vs. cold season
Z Migratory birds have a more complicated cycle
• Many times, two molts are necessary
• After breeding (where they live as pairs), they:
Molt (the spring molt usually does not include the flight feathers)
Gather in flocks
Eat lots of food
Change physiology in preparation for the flight
Fly to wintering grounds
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• When they arrive at the wintering grounds, they:
Return to normal physiologically
Live through the winter in loose flocks
Molt
Eat lots of food
Change physiology in preparation for flight
Form flocks again and will separate into pairs upon arrival at the breeding grounds
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• There is great variation on these basic patterns among species and even among subpopulations within species
All is dependent on geographical location and the associated climate of that region
Z Reaction to photoperiod (day length) is the ultimate source of control of annual cycles
• Environmental light stimulates photoreceptors and the brain basically keeps unconscious track of whether days are getting longer or shorter
• A circadian cycle (daily) measures day length
The onset of sunset or sunrise triggers release of chemicals (primarily melatonin) in the brain that causes the body to prepare for either increased activity or sleep
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Z Ultimately, this system has evolved to allow birds to:
1. Respond to mean optimal time for reproduction (when in most years environmental factors are prime for rearing young) 2. Synchronize reproductive function in mated pairs 3. Terminate reproductive function
Z The pineal gland (small, and embedded within the brain) seems to be the center of control for these circadian and annual cycles (biological clock)
In primitive reptiles and other lower evolutionary groups, the pineal gland has its own photoreceptor visible on the “forehead” so light information is gathered directly
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Migration Z Migration – the periodic passage of groups of animals from one region to another for feeding or breeding
Z Migration usually happens in annual cycles • In contrast, dispersal is a one-way, usually one-time movement from natal territory to new territory
• About 5 billion landbirds of 190 species migrate from Europe and Asia to Africa
• About the same number of birds of 200 species migrate from N. America to C. and S. America annually
Z Birds do this rather than become dormant or hibernate, which is what many amphibians, reptiles and mammals do to cope with winter or dry season
• Birds generally migrate north-south in the New World following geographic trends of mountains, river valleys, and shorelines
• Birds generally migrate somewhat east-west in the Old World following shorelines (North Sea, Mediterranean Sea), mountains (Alps), and deserts
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Z Why migrate?
• Cost of migration is high
About half the landbirds that migrate from N. America never return
About 100 million waterfowl in N. America migrate to southern wintering grounds and only about 40 million return to breed
1. High energy cost
2. Exhaustion kills many
3. Hurricanes and sandstorms are a problem for those crossing oceans and deserts
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• Reasons migration may be beneficial:
1. Escape from inhospitable climate
Not critical for some species as many species do not migrate and can endure harsh winters
But, there are limited resource in winter, so species suited to survive and gather resources don’t need to migrate
2. Probable starvation as winter foods are limited
Their over-winter destination will have abundant food available
3. Shortage of roost sites
Some species can remain in the winter but not all due to limited protective cover
Z Some species change their migration habits as some populations stop migrating and some begin
• Cattle egrets were confined to Africa 100 years ago
They follow the distribution of introduced cattle to the New World and are found almost exclusively with cattle where they eat insects as cows graze
First, they began migrating from Africa to S. America
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Soon, some populations began migrating to N. America
They now follow various migration routes and some populations are residents
• Some barn swallows (common in N. America) in Argentina are now residents, but in the past they would migrate back to N. America
Z Overall, birds that migrate to the tropics from temperate zones survive the winter better than year-round residents of temperate zones
Cattle Egret distribution Green – year-around Blue – Winter (non-breeding) Yellow – Summer (breeding)
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Z Tropical residents trade low productivity for high survivorship
• Nesting space is limited in the tropics because of high density of birds, so they may have to wait several years for a nesting space
• In comparison, temperate populations occur in low density and breeding space is not limited
They turn out many young but survival is lower due to migration or winter mortality
Z Benefits of migration are species specific and, through evolution, the they find a “best” strategy
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Population Dynamics
Z Most birds have incredible reproductive potential, as do many other vertebrate animals
• One American Robin producing 2 broods of 4 eggs per season will leave 24,414,060 descendents after 10 years (assuming all survive and have the same # of offspring)
• The Passenger Pigeon (now extinct) in 1871, had one colony of about 136 million breeding birds over 850 sq. mi. in Wisconsin
• One flock was estimated at 2 billion birds
• Last individual died in Cincinnati Zoo in 1914, but the last known colony was in Wisconsin in 1885
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Z If all offspring or nearly all survive, we would be overrun with birds
Z Sometimes when a species is introduced into new territory, their numbers at first skyrocket (exponential population growth) and then level off at a number the environment can carry (logistic population growth)
• Usually, the only time this is an ecological problem is when new species are introduced to an area from other zoogeographic zones, called exotic species
• All organisms need space to live, food, water, and nutrients to survive, and other species are competing for the same resources
• All populations of organisms have:
Biotic potential (r) – a maximum rate at which their numbers can increase
Environmental factors (K) that work against their population numbers
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Z For birds, biotic potential is dependent on:
1. Number of eggs/clutch
2. Number of clutches/season
3. The age when that species begins breeding
4. Longevity (how long individuals live on average)
Z Birds lay between 1-20 eggs/year and can attain sexual maturity between 12 weeks and 8 years of age
• A species with long-delayed sexual maturity must have a compensating long life-expectancy
Z Larger broods can be beneficial because more chicks in a brood reduces heat loss/chick and less food and heat from the parent is required
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• There are several downsides to large broods:
1. Greater physiological exhaustion of parent (lots of work)
2. Higher population densities in the next generation may reduce life-expectancy of individual birds as food, nesting sites, and territory may be more limiting
3. Chicks in larger broods have reduced life-expectancy since each one is given less resources by the parent
• Clutch size tends to be the population regulating factor for most bird species
This is the life history trait that is modified to cope with changing environmental conditions
Z Longevity of some bird species in the wild (information is from banded wild birds):
Ruby-throated hummingbird – 5 years House wren – 7 years House sparrow – 10 years American robin – 11 years Red-winged blackbird – 14 years Red-bellied woodpecker – 20 years Barn owl – 21 years Brown pelican – 31 years Golden eagle – 25 years Canada goose – 23 years Osprey – 32 years Laysan albatross – 42 years
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Z The life history strategy (brood size, longevity, sexual maturity, mating system, parental care patterns, etc.) that a species exhibits is the strategy that has been shaped by evolution: it is what currently works for that species
• If conditions change (climate, introduced competitors or predators, suitable habitat destroyed by humans, etc.), a species may respond by altering one or more life history characteristics
• Sometimes a species simply can’t change its life history fast enough and goes extinct
Sometimes this is a natural event, many times now it is heavily influenced by humans
Z If biologists understand what the parameters are of a particular species, they can manage it as a sustainable resource
• Or in cases of pest species, they may be able to find the parameter that is most important to population growth and reduce it as much as possible
We have problems with some species as agricultural pests (blackbirds on grain fields, fish-eating birds on aquaculture ponds)
One of the best ways to deal with them are to take away roosting and nesting sites near fields and ponds
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• It is almost never a good solution to simply eliminate the adults because survivors will compensate by increased reproductive effort
Cormorants roosting in a Mississippi Delta slough near catfish ponds
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W A good example of sustainable harvest is bobwhite quail population management (same for waterfowl)
• We know bobwhite quail have about 70% natural mortality each winter so if you harvest 35% of the population then 35% will die of natural mortality
• The portion harvested is called compensatory mortality
• If harvest goes above natural mortality then it is called additive mortality
• We usually set bag limits and seasons so hunting mortality is never very close to natural winter mortality
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Endangered Birds of Mississippi
Z Federally Endangered
• Wood Stork • Red-Cockaded Woodpecker • Mississippi Sandhill Crane • Ivory-Billed Woodpecker (may be extinct in the U.S.) • Brown Pelican • Bachmans Warbler (may be extinct in the U.S.) • Least Tern
Z Others
• Piping Plover (Federally threatened in MS) • Snowy Plover • Bald Eagle (downgraded to threatened 1994) • Peregrine Falcon (downgraded to threatened1999)
Piping Plover Snowy Plover
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Z Wood Stork
• Considered a visitor in MS but presence may be more substantial • 150,000 estimated in FL in 1930 down to 12,000 estimated total population • Draining of wetlands primary cause of decline
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Z Red-Cockaded Woodpecker
• 4,800-10,000 estimated in 1978 and known to have declined since • Decline due loss of longleaf pine forest (80-90% loss since early 1900 • Must excavate cavities in old-age, living pine
Z MS Sandhill Crane
• As of 2000, 110-120 cranes in the wild with 40 in captivity at Audubon Research Center in LA and White Oak Conservation Center in FL
• Primary reason for decline is loss of longleaf pine- wetland savanna habitat
• Other reasons include shooting and coyotes
• MS Sandhilll Crane NWR (18,000 acres) created in 1975 for recovery
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Z Ivory-billed Woodpecker
• Now probably extinct
• Depended on standing, dead old-growth hardwood trees in bottomland hardwood habitat for cavities and food, wood-boring beetle larvae
• Reports of sightings in Cuba and the White River NWR in Arkansas have not been substantiated
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Z Brown Pelican
• Have been downgraded to threatened in some states because of increasing populations since the 1970s
• Populations plummeted in 1960s from long term use of DDT, an insecticide to control mosquitoes
• Adults were poisoned and eggs had thin shells
Z Bachmans Warbler
• Was probably always rare and now may be extinct
• Last confirmed sighting in Cuba in 1980
• Loss of old-growth bottomland hardwood forests was probably main cause of decline but we are not sure
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Z Least Tern
• Elimination of sandbar nesting habitat from reservoir construction and channelization of rivers has caused decline
• Release of water from dams flood sandbars downstream and destroy eggs and chicks
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