ZOO 435 Lecture - General Characteristics of Extant Birds

 Forelimbs are wings (in all birds); most can fly  Feathers and leg scales (epidermal structures)  No sweat glands  Uropygial gland present in most  Rudimentary pinna (fleshy ear)  Skeleton fully ossified; air sacs in bones; strutting for strength  Cervical vertebrae have saddle-shaped articular surface – very flexible  Single occipital condyle (flexible)  Jaws covered by beak (keratinized sheath)  No teeth  Well developed brain and nervous system  Optic lobes and cerebellum very well-developed  Excellent eyesight – can see color, UV, and polarized light o Golden Eagle can see a rabbit two miles away; 1500 feet for people  Poor sense of taste and smell (with some exceptions)  12 pairs of cranial nerves (just like mammals)  4-chambered heart; Right aortic arch (IV) persists  Reduced renal portal system (Blood from the posterior part of the body flows into the renal portal veins, which pass into the caudal vena cava. The renal portal system is found only in fishes, amphibians, reptiles and birds. Thus, mammals have no renal portal system. All that remains in mammals is the azygous vein, which is an unpaired vein that drains most of the intercostal space on both sides of the mammalian thorax.)  Nucleated red blood cells  Crop – diverticulum of the esophagus (allows ingestion of food which can be stored until a safe place is found for digestion)  Proventriculus – distal portion of the stomach (closer to mouth); initiates digestion;  Ventriculus (gizzard) – proximal portion of the stomach (farther from mouth); muscular walls to grind and crush, often aided by sand or gravel  Air sacs among viscera and in skeleton  Voice box = syrinx; located at proximal end of trachea, at junction with bronchi  Cloaca; no bladder; semi-solid urine; nitrogenous waste = uric acid  Female with only left ovary and oviduct (exceptions, e.g. hawks)  Internal fertilization; most males lack intromittent organ usually lacking (exceptions: e.g. ducks; ostrich)  Oviparous; amniotic egg; calcified shell; yolk for energy; albumen (egg white) acts as a cushion; respire through shell (only a day or two before hatching)  Endothermic; body temp between 100 – 133 degrees F; high metabolic rate

 ZW sex determination (not XY system) o ZZ = males; homogametic; ZW = females; heterogametic o Also found in some fish; insects (butterflies; moths) o Ovum determines sex of offspring o Unknown whether W produces female characteristics; OR double Z produces male characteristics o No birds with double W or single Z (Z0) have been discovered o ZW chromosomes are autosomal in mammals; and vice-versa . ZW and XY couples may come from different chromosomes of the common ancestor; the two systems may be related somehow  Small genomes (chicken = 1.2 billion base pairs; people = 3.5 billion bp) o TRANSPARENCY  But birds tend to have lots of chromosomes; but tend to be vastly different sizes o Macrochromosomes and microchromosomes o Diploid number of chicken = 78 (38 pairs of autosomes; pair of sex chromosomes) . Diploid number of people = 46 (23 pairs autosomes; sex chr.)  Mitochondrial genome: 16,800 bp; 13 genes o People: 16,600 bp; 37 genes