Dinosaur and bird respiratory systems
Credit: Zina Deretsky, National Science Foundation
It is generally accepted that birds evolved from reptiles and, as a consequence, have been described as being nothing more than warm blooded, feathered, flying reptiles. While this holds true for most species of birds, evolutionary progress has produced some that do not fly.
Prehistoric bird fossil
Reptiles and birds have many similarities. They both reproduce, in the main, by laying eggs, they both have scales and neither has a urinary bladder. It is believed that, during the period of their evolution when environmental temperatures dropped, those reptiles that survived such a harsh climate by modifying their scales (by splitting) to form feathers and so maintain body temperature became the ancestors of birds. The feathers provided a layer of still air between themselves and the body and this helped maintain body temperature. The splitting of the scales provided other benefits - they aided in maintaining balance during fluttering which, in time, developed into an ability to soar and ultimately to fly.
In addition, certain of the reptilian forerunners of today’s’ birds possessed characteristics more suited to flight than did others. The egg laying habit and the absence of an urinary bladder also aided flying. Reproduction by laying eggs meant that the female did not have the added weight of her offspring during it’s embryonic development and the absence of a bladder meant that urine did not accumulate prior to it’s passing thus lightening the load. In fact, the urine passed by birds is of a pasty nature as they re-absorb much of the water so reducing their dependence on water supplies.
Avian airsacs
Aspects of evolutionary change that enhance the birds ability to fly are:
1. Air sacs and pneumatic bones – the bronchi of the respiratory system extend beyond the lungs into air sacs which in turn extend into many long bones. These air sacs:
o Reduce the weight as an aid to flight;
o Help the bird to change the centre of gravity as it changes posture from the fairly upright when not flying to the generally horizontal when flying;
o Provide volume in the respiratory system for the large volume of air to provide the oxygen necessary for the energy required for flight.
2. Major parts of the vertebral column are fused to provide a strong, rigid framework for the large muscles involved in flight to work against e.g. the bones of the lumbar and sacral regions are fused.
3. The head is attached by a long, flexible, ‘S’ shaped neck as a means of:
o Adjusting the centre of gravity during flight;
o Reducing concussion on landing to protect the brain and nervous system;
o Facilitate feeding from the ground - this would be otherwise difficult because of the rigidity of the body.
4. The extremely deep sternum or breast bone for the attachment of the large muscles that in flight raise and lower the wing.
5. The provision of a very simple but highly efficient digestive system that, while being light, will support the high metabolic rate.
6. The streamlined shape of birds:
o Generally rounded for better aerodynamics;
o Folded skin to minimise angles and to eliminate pockets during flight;
o Legs are usually folded up against the body to minimise their effect on airflow.
Animals and plants are classified for scientific purposes in a way based on the premise that the more alike two representatives are, the closer they are likely to be related. As a result of this classification system, all animals and plants (and other forms of life) are given a scientific name that permits the recognition by trained personnel of the various relationships to other similar plants and animals. The classification system is organised in a hierarchal arrangement that recognises closer and closer relationships in a descending order thus indicating an increasing resemblance of design and history.
The hierarchal arrangement of this classification system is as follows:
i. Kingdom - the plant and animal kingdoms
ii. Phylum - plants or animals with overall general similarity
iii. Class
iv. Order
v. Family
vi. Genus
vii. species
In this system the lower down the order the closer the relationship. Plants and animals are described by their Genus and species and those with the same Genus and species name are the same while those with the same Genus name but different species are very closely related. This system has been shown to be inadequate and the use of prefixes “super” and “sub” eg. super-class or sub-class etc allows for the further sub-division of these categories.
Following this system of naming, some common species of domestic birds are named as follows:
· Domestic fowl - Gallus domesticus
· Domestic goose - Anser domesticus
· Domestic duck - Anas boschas domesticus
· Domestic pigeon - Columba domesticus
· Domestic turkey - Meleagris gallopavo
· Guinea fowl - Numida meleagris
Micro-organisms are classified in this way also eg. the organism (a protozoan) that causes coccidiosis belongs to Emeria and caecal coccidiosis is caused by Emeria tenella and the bacteria that causes colibacillosis is called Escherichia coli.
Red Jungle Fowl
The domestic fowl originated from the wild jungle fowl that is still found in the jungles of some parts of south east Asia. The wild jungle fowl, Gallus gallus (there are a number of sub-species) was first domesticated in the foothills of the Himalaya Mountains approximately 5000 years ago. They were probably first kept in captivity to supply food for their owners, for sport and to satisfy a desire to own.
As time passed, the practice of keeping fowls spread through Persia to the Mediterranean countries in the west and through Asia to China in the east. Owners in close proximity to each other selected their breeding stock for particular characteristics in their birds and so there developed in these different localities a type of bird based on appearance that was peculiar to a locality. These groups of birds with the same characteristics became known as breeds, the breed name usually being the name of the region of their development e.g. the leghorn breed was developed originally in the Leghorn district in Italy.
Modern Layer hens
Source: Australian Egg Corporation Limited
A breed can be defined as a group of fowls that reproduce their own likeness in their offspring. In some cases, differences in one or two characteristics appeared eg. in comb shape or feather colour. These different types within a breed are varieties e.g. white and brown leghorns are well recognised varieties of the leghorn breed.
There are many breeds of fowls, but only a small number are used to breed the commercial birds that the modern poultry farmer is familiar with. In the commercial poultry production world there are two types of bird - the egg type and the meat type. These are so described not because they are restricted to producing one or the other product but because they produce either eggs or meat more efficiently. They both produce eggs and meat, the difference is in how well they produce these commodities in the commercial sense. These types are derived from the more traditional breeds that are combined in different ways and selected for particular characteristics over a number of generations ending up as the commercial egg layer or meat bird. Selection for the improvement of the economically important characteristics is an ongoing activity in poultry breeding programs.
The start of the poultry industry was most likely based on the village flock where ownership was more on a communal basis with the birds running free by day and perching in trees as a protection against predators at night. It was but a short step to confine the birds to an enclosure at night for protection. In many developing countries today the typical village flock plays an important part in day to day living. In these situations the birds forage for their nutritional needs and are given household scraps if these should be available. This same situation exists with farmyard flocks. Over time and as the domestic fowl spread to other cultures, ownership became more of a personal activity and small flocks owned by individuals or house holds the forerunner of today’s poultry industry.
The first innovation after the night shelter was the provision of an enclosure to provide continuous control and protection. This meant the birds could no longer forage freely seeking their nutritional needs from natural sources. All of their nutritional needs had to be supplied by the owner. This method of housing poultry persisted for a long time and is used today for the production of “free range eggs” and “free range meat”. The size of the flock in this situation is largely based on the number the individual farmer can care for - the system is quite labour intensive.
It was soon found that birds managed more intensively performed better than those left to forage, particularly where the nutritional needs were met. However, there was a penalty for the increased density used - that of an increase in the incidence of disease. When populations of animals are housed at high densities, it provides an ideal situation for the concentration and transfer between individuals of infectious disease causing organisms.
Modern broiler shed
It has been the concurrent improvements in housing and equipment, nutritional practices, genetic potential, disease control and management techniques that has allowed the successful implementation of the techniques used today. Poultry are now kept in large flocks in technologically advanced housing systems utilising any of the following - cages; litter housing; slatted floor housing; environment control including automatic, electronically controlled systems; mechanical feeding and water supply systems; mechanised manure handling; mechanised egg collection and processing; mechanised bird handling; electronic recording systems and highly specialised management techniques. These advances allow for the collection of large quantities of information on which to base decisions, reduce the dependence on expensive labour and the provision of a more responsive management system for the stock.
The modern poultry industry is based mainly on large scale production units producing either eggs or meat. Production stock have a very short life and replacement stock are produced by a small number of large breeding operations. Till recently, the commercial stock have been bred in Australia. However, over more recent times, genotypes suited for the production of both commodities have been imported through the quarantine facilities built for that purpose in southern states (Torrens Is. in South Australia - live birds; Melbourne - fertile eggs). The Australian Poultry Industry, while being very small is very efficient utilising the most modern equipment and techniques. It is universally regarded as the leader of the animal industries in the introduction of new technology.
