chapter 2 - Chapter 2: Biological Systems of Birds There...

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POSC 201 – Chapter 2 Page 1 of 34 Chapter 2: Biological Systems of Birds There are ~100 billion birds on earth and only ~6 billion people for a ratio of ~17:1. The chicken is the most numerous domestic bird (~30 billion). The scientific name of our domestic chicken is Gallus domesticus (genus / species). Gallus domesticus is thought to be genetically derived from 4 wild species still found throughout Southeast Asia (see map below): * 1) Gallus gallus (Red Jungle Fowl) 3) Gallus lafayettii 2) Gallus varius 4) Gallus sonneratii *Considered to be the greatest genetic contributor to Gallus domesticus Map of Southeast Asia indicating regions where four wild species of Gallus are still found.
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POSC 201 – Chapter 2 Page 2 of 34 All the varied breeds of domestic chickens are the result of mutations or human selection pressures applied to the “gene pool” of these four wild species (similar to the varied breeds of dog being the result of mutations / human selection pressures being applied to the “gene pool” of the wild wolf ). The first known bird, from archaeological records, was Archaeoptryx which lived during the Jurassic period ~150 million years ago. From fossil records we have determined that this bird was about the size of a crow, had teeth and also had claws on its wings to aid in climbing. (See drawing below). To put time in some sort of prospective, consider the following: Universe ~ 14 billion yrs. old Earth ~ 4 billion yrs. old One cell life forms ~ 3 ½ billion yrs. ago Dinosaurs ~ 250 million yrs. ago (until ~ 65 million yrs. ago) Birds ~ 150 million yrs. ago Homo sapiens ~ ½ million yrs. ago TAMU Aggies Big 12 Football Champions ~ Next year Fossil Line drawing of Archaeoptyrx
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POSC 201 – Chapter 2 Page 3 of 34 ANATOMY / PHYSIOLOGY OF GALLUS DOMESTICUS (with emphasis on features peculiar to birds) Skeletal system : Vertebra of the neck (cervical) region articulate to allow free movement of the head which facilitate food collection, visual observations, fighting and also access to their preen (oil) gland. Vertebra of the main body (thoracic and lumbar regions) are fused to provide the necessary rigidity of the main body (air frame) to allow flight. The fused lumbar vertebra are flanked by 3 lateral flat boney structural developments called the ilium, ischium and pubic bones. Vertebra of the tail region articulate to allow free movement of tail feathers so necessary to control direction of flight.
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POSC 201 – Chapter 2 Page 4 of 34 Long bones of flight birds are essentially hollow which reduces body weight for flying. Some of these hollow bones are also pneumatic (i.e. connected to the respiratory system to increase air breathing capacity.) In addition, these hollow long bones in females become medullary at the time of egg laying as a result of elevated blood estrogen levels (see illustration below). These calcium stipules provide calcium for egg shell formation (males will also form calcium stipules if given estrogen injections). Hollow long bone of female bird with calcium
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This note was uploaded on 09/20/2011 for the course POSC 201 taught by Professor Krueger during the Spring '11 term at Texas A&M.

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chapter 2 - Chapter 2: Biological Systems of Birds There...

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