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HOW EGGS ARE FORMED by J. BeauSoleil (pronounced Bo' So La) NOTE: Copyrighted material which cannot be reproduced in any form without author's written permission. Reproduction in birds is a fascinating study and has many similarities to human reproduction but yet quite different; simple yet complex. All the genetic makeup and food supply is packaged neatly together into a shell to produce the next generation of that species. Anyone who's examined an egg can see the primary parts consist of: *white (albumen) which protects and cushions the developing embryo *yolk which provides nourishment to the developing embryo through connecting blood vessels (which are seen when candeling) *ovum (small opaque spot at corner of yolk) if fertilized becomes the embryo once incubation is started *shell which packages together all the above. REPRODUCTIVE TRIGGERS The ovum (future chick if fertilized & incubated) remains inactive until "increased seasonal light" absorbed through eyes AND extraretinal receptors in soft spongy bone structure of the head of the hen, triggers follicle-stimulating hormones (FSH) to kick into gear. (decreased light has opposite effect causing depression of follicle growth & egg production ceases--see article "Importance of Full-Spectrum Lighting"). As the sexually mature hen is stimulated into reproduction, the ovum is held in the follicle on the ovary where the yolk develops over a period of several days. Once mature, the ovum with its yolk ruptures free of the ovary to begin the 24-to-26 hour journey down the reproductive tract. THE JOURNEY 1) Fertilization of the ovum (if it's to take place) occurs in the upper funnel end of the oviduct, call the infundibulum, also referred to as the sperm pocket. This fertilization process takes approximately 15 minutes. 2) Then the fertilized ovum travels to the magnum where it spends approximately 3 hours while the albumen protein (egg white) is secreted. 3) Further down the tract in the isthmus, two shell membranes are secreted loosely around the ovum and albumen, which takes approximately 1-1/2 hours. 4) This soft egg continues its journey into the uterus (shell gland) where it stays for 20-21 hours while the shell is secreted in layers over the membrane. 5) Once shell is fully formed and hardened, the egg is then passed immediately through the vagina where it is 'laid'. Again this total process takes 24-26 hours from time ovum starts down oviduct. As one egg is finishing the journey, another one is starting, repeating until full clutch is laid. Eggs of most psittacines are laid every other day. Clutch sizes vary with different species but most average 3-5 eggs per clutch. Occasionally there will be a delay where several eggs accumulate in the oviduct at the same time which causes eggbinding, and/or premature expelling of soft shelled eggs. If eggs are rushed or pushed through the uterus (shell gland) prematurely, the hard shell covering is absent. THE FUNCTIONS As egg is incubated and growth begins, the embryo (blastoderm) forms three separate layers; within each layer the development of separate body parts takes place: 1) The inner layer is composed of the organs, digestive tract and more. 2) The middle layer forms the muscles, bone, blood, reproductive system. 3) The outer layer forms the skin, feathers, beak, eyes, nervous system. INTERESTING NOTES ABOUT EGGS *While in the uterus, all egg shells are white. The addition of the various colors of different species occurs after the egg leaves the uterus, just before it is laid. (gently rub a brown chicken egg with sandpaper and the white shell will be visible) *Unlike human reproduction where sperm determines sex; in birds the sex is predetermined by the hen BEFORE ovulation and BEFORE ferilization occurs. This, according to Harrison & Harrison, is because female is heterozygous whereas male is homozygous. *Unlike reptile eggs where sex appears to be determined by incubated temperatures (more males at warmer temps, more females at cooler temps); this does not occur with birds, because again sex is predetermined before egg is ovulated & fertilized. Amazons Subspecies/Avian Nutrition/Full-Spectrum Lighting/How Eggs are Formed/ Breeding & Egg Handling/Behavior & Speech Training/About Us/The ParrotCove Gang/Links/Web Rings Information supplied in this article is expressed opinion of author who believes to be true after extensive research.