2Skeletal SystemSkeleton is very unique and specially adapted for flightVery lightweight; yet strongMost of the long bones are hollow but reinforced through a honeycombed structureFlying species have a large keelKeel - place on the sternum that the flight muscles attach
4Respiratory System Different from mammals in many ways. Bird respiration is much more efficient.Birds do not have a diaphragm. In mammals this moves up and down to increase and decrease the chest cavity.Birds push the sternum in and out to the same effectHummingbird breathes 143 times per minute while a turkey breathes 7 times per minuteRate increases during flight.
5Breathing CycleBird lungs are very compact and take up much less space than mammal lungsThe air enters through the nostrils, down the trachea and into the lungs and air sacsThin-walled air sacs extend through the body cavity and even into the bonesBirds can keep a continuous flow of air through the lungs.
7DigestionBirds has special digestive tracts because they do not chew their foodFirst the food travels down the esophagus and into the crop.The crop is an expanded section of the esophagus.It is used as a holding tank for food before it can enter the proventriculusThe proventriculus produces acid and adds enzymes which aid in breaking down the food
8The gizzard helps grind food like seeds The gizzard is highly keratinized to make the surface roughTurkey gizzard can crush walnuts and steel needlesFood then passes through the intestinal tract, where nutrients are absorbedWaste is expelled through the cloaca, or vent.
11Reproductive TractThe reproductive organs shrink whenever birds are not in breeding seasonThis decreases their weightMales have 2 testes and females have 1 ovaryEggs production:The ovum is fertilized and passes through a long tube called the oviductEach section of the oviduct adds a different part to the egg, just like an assembly line
12The egg assemblyIn the infundibulum the egg stays 20 minutes before going to the magnum where the egg white is addedNext the egg goes to the isthmus, where inner and outer membranes are formedThis process takes about 1 hourIn the uterus the shell and all pigments are added (20 hrs)The egg then passes out the cloaca