Z203/ Unit 5 Ch 27: Birds (Class Aves)

Z203/ Unit 5 Ch 27: Birds (Class Aves) I. Diversity A. Ornithology - Study of endothermic feathered tetrapods - Vertebrates with highly modified bodies for sustained flight - Significant changes in skeletal/muscle, circulatory & respiratory systems, integument, and reproduction B. Profile - over 9,700 species described; only fish have more species - live in all biomes; mountains to prairies, on all oceans (North to South pole) - some live in dark caves or dive to 45 meters - bee hummingbird is one of the smallest vertebrate endotherms (1.6 g. 2.5 inches long) - unique feather is hallmark of birds - uniformity is structure: despite evolving 150my, all are still recognized forelimbs modified as wing, though not always functional hind-limbs adapted for walking, swimming, perching all birds have toothless horny beaks (layers of keratin) all lay eggs (oviparous) flight = driving force for uniformity a. wings to support & propel b. respiratory system meets demands of O 2 requirement & cool body c. bones lightweight but rigid airframe d. digestion & circulation meet demands of flight e. nervous system has superb sensory system for high-velocity flight conservation of design; unlike mammals have developed far more diverse forms 1

II. Origin & Relationships A. History 1. discovery of fossil Archaeopteryx lithographica (Jurassic aged) in 1861 linked birds & reptiles a. skull resembles modern birds but w/ teeth b. reptilian skeleton w/ clawed fingers, abdominal ribs & long bony tail c. feather imprints along the wings 2. Zoologists had long noted similarities between birds & reptiles. Both have: a. skulls that abut 1 st vertebra w/ ball-andsocket joint (1 occipital condyle) b. single middle ear bone (stapes) c. lower jaw composed of 4 or 6 bones d. excrete uric acid e. similar amniotic cleidoic eggs & development 3. Thomas Henry Huxley classified birds w/ therapod dinosaurs a. group of dinosaurs w/ long, mobile S-shaped neck b. therapods belong to diapsid lineage (archosaurians) which include crocs c. fossil evidence from Spain, China, S. America support this link 2

III. B. Relationships 1. modern birds include: Paleognathae (flat sternum: ostrich, kiwi, rhea, emu) (keeled: penguin) Impennes Neognathae (keeled sternum: modern birds) New jaw no teeth 2. appears flightlessness evolved several separate independent times 3. larger flightless birds (ostrich & emu) became fast runners 4. flightlessness freed birds from weight restrictions (sizes varied, many very large) Form & Function A. Feathers 1. Structure - contributes to more power & less weight - hollow quill emerges from skin follicle & continues as a shaft or rachis - rachis bears numerous barbs - hundreds of barbs arranged in flat, webbed surface, the vane - each barb resembles a mini-feather numerous parallel filaments or barbules spread laterally up to 600 barbules on each side of barb (may be millions in one feather) barbules overlap; they zip together w/ tiny hooks (preening zips) 3

2. Types of Feathers - Contour feathers provide form - Flight feathers extend off wing in flight - Down feathers under contours; barbules lack hooks, function in insulation - Filoplume feathers hair-like, degenerate feather w/ weak shaft & tuft or short barbs - Powder-down feathers on herons & relatives disintegrate & release a talc-powder to waterproof - Bristle feathers found on the head, hace a stiff rachis w/ few barbs. Used for sensory & protection 3. Origin & Development - homologous to reptile scale - develops from epidermis, nourished by dermal core - during growth, pigments added to epidermal cells - near end of growth, soft rachis & barbs keratinize - when protective sheath splits apart, feather protrudes & barbs unfold 4. Molting - full-grown feather is dead; shedding or molting cyclic - gradual (except in penguins) molting avoids bare spots - flight & tail feathers lost in pairs on each side to maintain balance - some species, molt continuous so doesn t impair flight - many water birds, primary feathers molted all at once & birds grounded temporarily - most molt once a year, usually in late summer after nesting season 4

5. Color - color due to pigments or structural reflective nature - pigments (lipochromes) color red, orange, yellow - melanin yields black, brown, redbrown, & gray - blue color is from scattering of light (reflected light) - Colors may vary between sexes (sexual dimorphism) B. Skeleton 1. Bone Weight - light, delicate bones laced w/ air cavities = pneumatized (still very strong) - overall reduction in number of bones ( many fused: tibiotarsus, carpometacarpus) - total weight of feathers outweighs skeleton 2. Skull - fused into one piece, the braincase & orbits enlarged - skull lighter; legs heavier than mammals; lowers the center of gravity 3. Jaws - horny keratinous beak molded around bony jaws - most have Kinetic skull; in some, upper jaw hinged to skull - less kinetic than reptilian skulls 4. Vertebrae & Appendages - vertebral column rigid, most vertebra fused except for cervical vertebra - synsacrum (rear of pelvis) is fusion of 13 vertebra w/ pelvic girdle to support legs & provide rigidity for flight 5

- uncinate processes interlock the ribs & give torso strength - ribs mostly fused w/ vertebra, pectoral girdle & sternum - sternum bears large Keel for anchoring flight muscles (not seen in flightless birds) - forelimbs reduced in number or fused for flight - - * humerus, ulna, radius present * hand reduced to 3 digits legs have undergone less modification; function still walking, etc. feet modified to habitat * reduced to 4 digits C. Musclular System 1. pectoralis muscles attached to keel, down stroke of wing 2. supracacoracoideus muscle attached to keel, work as a rope- &-pulley to raise wing 3. location of both flight muscles gives them aerodynamic stability - center weight under wings 6

4. main leg muscles in thigh, attach to long tendons to feet & toes 5. toe-locking mechanism prevents perching birds from falling when sleeping 6. lost long reptilian tail & substitute a muscle mound where tail feathers rooted on pygostyle (fused caudal vertebra) 7. as many as 1000 muscles control tail feathers for steering in flight 8. interwoven stringy muscles in neck give flexibility D. Food, Feeding, & Digestion 1. Insects Eaters - earliest birds appear to be insectivores - specialization has occurred for specific prey 2. Other Diets - nearly 1/5 th of birds feed on nectar - beaks specialized to specific foods; chisel-like woodpeckers bill has tongue extend @ head - seed-eaters crack shell (bulky bills) - fish-eaters modified bills (serrated, scoop, spear-like) 7

3. Food Quantity - have voracious appetites to sustain endothermy & high MR 98% of energy budget used in temp maintenance - hummingbird uses O 2 12x s faster than pigeon & 25x s that of a chicken - hummingbirds eat 100% of body wt/day, blue tit eats 30% while chicken eats 3.4% - rapid and efficient digestive system: shrike digests a mouse in 3 hours thrush can pass berries through tract in 30min - salivary glands are poorly developed (moistening occurs in crop) & few taste buds (limited taste) - long, muscular esophagus extends from pharynx to crop - crop serves to store & moistens food - crop of pigeons, doves, & parrots produce lipid & protein rich milk from shedding lining - stomach (proventriculus) secretes gastric juices - some birds swallow pebbles or grit to assist grinding in gizzard (since toothless) - birds of prey eject pellets of undigestable material (owls lack a crop) - length of small intestine mirrors food types (shorter in carnivores, longer in herbivores) - paired ceca at junction of intestine & rectum serves in fermentation (important to herbivores) - cloaca at end of digestive tract also receives products from genital ducts & ureters 8

E. Circulatory System 1. 4-chambered heart w/ strong ventricular walls & overall sizes is slightly larger in comparison to body mass (0.2%) (chicken heart vs. human) 2. share complete separation of pulmonary & systemic circulations w/ mammals 3. right aortic arch leads to dorsal aorta (instead of left as in mammals) 4. 2 jugular veins have cross shunts to continue circulation as head rotates 5. unusually large arteries deliver lots of bloo d to breast & wings 6. fast heartbeat inversely proportional to size a. turkey heart rate 93 beats/min b. chicken HR 250 beats/min c. chickadee HR 500 beats/min d. humming bird HR over 1000 beats/min humans average 70 beats/min 7. RBC (erythrocytes) nucleated & biconvex 8. WBC mobile (phagocytes) active & efficient in wound repair & immunity F. Respiratory System 1. unique design differs radically from reptiles & mammals 2. lungs modified for one-way air flow & air storage: air enters typical pathway (nasal/mouth pharynx trachea bronchi) air bypasses lungs via bronchi & flows directly to posterior air sacs on inspiration 9

finest branches off of bronchi are tube-like Parabronchi located through the lung air sacs extend into thorax, abdomen & even long bones on expiration, air flows through lungs providing a continuous air flow takes two cycles for single breath of air to pass through the system most efficient respiratory system of any vertebrate 3. air sac system helps cool bird when up to 27x s more heat is produced 4. non-respiratory air sacs located in bones, legs & wings gives buoyancy & reduce overall weight of bird 10

G. Excretory System 1. pair of large metanephric kidneys composed of thousands of nephrons located in lobules 2. vertebrate pattern of glomerular filtration, loops of Henle for water/salt balance & selective reabsorption (like mammals) 3. urine flows through ureters to cloaca 4. Uric acid: use reptilian adaptation of uric acid nitrogenous waste is harmless w/in cleidoic amniotic eggs since low solubility, far less H 2 O for excretion excess water absorbed in cloaca kidney less efficient than mammals in removing ions of sodium, etc (loops of Henle shorter) concentrate solutes almost equal to or slightly higher than blood (mammals concentrate 4-25x s) marine birds excrete larger salt loads due to ingesting salty foods & salt-h 2 O salt glands located above eye & end in nostrils result in runny nose H. Nervous & Sensory Systems 1. well-developed cerebrum, cerebellum, & midbrain tectum 2. chief coordinating center (cerebral cortex) thin, unfissured & poorly developed 3. core of cerebrum enlarged into principal integrating center 4. cerebral hemisphere size related to bird intelligence 11

5. cerebellum houses proprioception, equilibrium sense & visual cues assembled 6. optic bulge each side of midbrain & forms visual association apparatus 7. sense of smell poorly developed except in flightless birds, ducks, & vultures 8. good hearing & superb vision; best in animal kingdom 9. ear similar to mammals no external ear flaps (pinna) external canal hidden in auricular feathers & leads to eardrum middle ear contains rod-like bone (columella) that transmits vibrations to inner ear inner ear has short cochlea, allows hearing in same range as humans can t hear high frequency like us but surpass us in ability to distinguish differences in pitch & intensity semicircular canals used for orientation and balance 10. eye similar to mammal eye but relatively large for body size eye less spherical & almost immobile; bird turns head instead of eye light-sensitive retina w/ rods & cones diurnal have more cones; nocturnal more rods herbivores have lateral eye placement to detect predators quicker birds of prey have eyes forward for depth Perception 12

many birds have 2 fovea e to provide sharp monocular & binocular vision hawk eye has 8x s the visual acuity (see a rodent over a km away) owl s nocturnal vision 10x s that of humans many birds see partially into UV spectrum (see flower nectar guides & urine trails from rodents) I. Flight 1. History - exploited habitat of flying insects - provided quick escape from predators & ability to seek better environments - 2 hypothesis to origin: a. ground-up based on running birds w/ primitive wings to snare insects b. tree-down based on tree-climbing, leaping, parachuting, gliding, & finally powered flight - feathers preceeded flight & arose probably for thermoregulation - three requirements for flight: a. Lift b. Thrust c. Drag 2. Wings provide Lift & create Thrust - modified hand bones w/ primary feathers providing propulsion (thrust) - wing shape (medial part of wing & secondary feathers) provide lift - wing streamlined w/ concave lower surface & convex upper surface - 2/3 of lift comes from negative pressure from airstream flowing longer distance over top, convex surface 13

- lift-to-drag ratio determined by angle of tilt & airspeed - as speed decreases, lift by angle of attack, & drag - at a point near 15 o, angle of attack become too steep & stalling occurs - stalling delayed or prevented by wing slots at leading edge to direct rapidly moving air across top in some, alula on the thumb provides midwing slot slotting provides wing-tip slots 3. Flapping Flight = provides Thrust - requires vertical lift & horizontal thrust - thrust provided by primaries at wing tips & lift by secondaries - greatest power provided by downstroke - primary feathers bent upward & twist to steep angle of attack - upstroke, primaries bend to provide thrust - powered stroke essential for hovering & fast, steep take-offs 4. Wing Forms reflect type of flight (aspect ratio: length to width) - Elliptical Wings (low-aspect ratio) maneuvering in forest habitats slotted between primaries to prevent stalling at low speeds chickadee can change course 0.03 sec - High-Speed Wings (high-aspect ratio) birds that feed on the wing or make long migrations wings sweep back & taper to slender tip, reduces tip vortex turbulence flat in section & lack wing-tip slotting 14

- Soaring Wings pelagic birds have long, narrow wings high-aspect ratio, lack wing slots & allow high speed, high lift & dynamic soaring highest aerodynamic efficiency of any design, but less maneuverable exp loit highly reliable sea winds & air currents of different velocities - High-Lift Wings birds of prey that carry heavy loads have wings w/ slotting, alula, & pronounced camber produce high lift at slow speed many are land soarers; broad, slotted wings allow sensitive response for static soaring IV. Migration and Navigation A. Migration - almost half of bird species migrate - move between southern wintering grounds & northern summer breeding grounds (latitude or elevational) - exploit seasonal changes in abundance of insects & avoid bird predators - appearing one time a year prevents buildup of specialized predators - expands living space & aggressive territorial behavior - favor homeostasis, avoiding climatic extremes & food shortages B. Migration Routes - most follow established N-S routes - may use different seasonal routes - journeys vary from short to long (60 days) - distance dependent on species and habitat requirements 15

- small species migrate at night, feed by day; others are daytime migrants - follow landmarks & other aids to navigate - Arctic tern circles N. America to Europe & Africa to winter for total 18,000km (11,200mi) C. Migration Stimulus - long day length stimulates anterior pituitary = development of gonads & fat accumulation - pituitary releases hormones that set in motion the sequence of migration, courtship, reproduction, & care of young D. Finding Directions - experiment suggest vision chief aid - recognize landmarks & follow familiar routes; may follow older birds - highly accurate innate sense of time & direction - experiment suggest incorporate magnetic fields too - Sun-azimuth orientation orientation cages show birds use sun at day & stars at night use the sun as a compass (determined using Planetariums) suggest North Star as an axis at night - migration involves combo of environmental & innate cues - natural selection culls individuals that make mistakes; only best navigators leave young V. Social Behavior & Reproduction A. Cooperative Behavior - sea birds gather in huge colonies to - land birds prefer isolation - congregate for migration & sometimes feeding nest & rear young 16

- advantages to flocking: mutual protection from enemies greater ease in finding mates less opportunity for migration straying mass huddling for protection against low temp - pelicans organize coop feeding behaviors - social interactions most noticeable during breeding B. Reproductive System - most bird species have non-functional reproductive organs outside of breeding season MALES: - testes recrudence, enlarge 300x s w/ approach of breeding season (shrink to pea size) - sperm stored in enlarged seminal vesicle - most males lack a penis; mating involves cloacal kiss - minimizes weight outside of breeding FEMALES: - most have only the left ovary & oviduct developed (right ovary & oviduct degenerate) - expand end of oviduct, infundibulum, receives the discharged eggs - special glands add albumin (egg white) to egg as pass down oviduct - shell membrane, shell & shell pigments secreted by lower aspects of oviduct & uterus - fertilization must take place in upper oviduct, prior to membranes & shell development - sperm remain alive in oviduct for many days to weeks after single mating 17

C. Mating Systems - over 90% of bird species are monogamous, one mate per breeding season - few species partner for life - small number of polygamous species - high rate of monogamy drove high degree of parental care ( like mammals) - female enforces monogamy be selecting male - bird territories: males sing to defend & announce territory female select male based on best reproductive success territory large enough to support one nesting female - polygyny m/c form of polygamy (1M + several F) male grouse collect on leks to display to females no male parental care competition intense & choose dominant male D. Nesting & Care of Young - nearly all birds lay eggs that must be incubated - require 2week to over a month incubation - may be laid in nest (open or cavity) or on bare ground - Brood parasites (cuckoos & cowbirds) lay eggs in other s nest - Precocial birds are able to feed & run/swim after being hatched - Altricial birds are naked & helpless at birth, must be fed in nest week or more - Nesting success in altricial species low; 20% of nests produce viable young - cause of nest failure include predators, parasites, & other factors 18

VI. Bird Populations A. Factors - populations vary in size from year to year - predators may cycle with prey supply (snowy owl vary w/ rodents they eat) - when food supply crash, birds move - humans have aided in dispersal: European starlings House sparrow Rock Pigeon - more than 80 bird species gone extinct since the 1695 dodo bird extinction - causes of extinction: habitat destruction & hunting - recent global declines in songbirds: agricultural practices forest fragmentation house cat predation loss of tropical forests (deprives 250 migrants of wintering homes) stress in wintering ground poorly prepares them for migration deforestation limits nesting ground VII. Classification of Modern Birds Subclass Neornithes Superorder Neognathae order Sphenischiform es order Gruiformes order Charadriformes order Gaviiformes order Podicipediformes order Columbiformes order Procellariformes order Musophagiformes order Pelicaniformes order Cuculiformes order Ciconiiformes order Strigiformes order Anseriformes order Apodiformes order Falconiformes order Coliiformes order Caprimulgiformes order Galiiformes order Trogoniformes order Coraciiformes order Piciformes order Passeriformes 19