BrokenWing Chronicles
Avian ReproductionReproductive Anatomy: * Gonads - paired testes in males & usually a single ovary in females
* Ovary
o most birds have only left ovary but 2 ovaries are typical of many raptors
o contains from 500 to several thousand primary oocytes
* Testes & follicles increase dramatically in size as the breeding season approaches.
o As day length increases, photic stimulation of the hypothalamus results in the secretion of Gonadotropin releasing hormone (GnRH below). When activated by GnRH, the anterior pituitary secretes two gonadotropin hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH acts on sperm-producing structures in the testes, while LH acts on the interstitial cells of the testes causing them to secrete the steroid hormone testosterone. The pituitary gland monitors the amount of testosterone in the blood, thus creating a negative feedback loop to maintain hormone levels within a set range (Akins and Burns 2001).
o Ambient visual cues, such as daylight, activate photosensitive loci in the brain both indirectly, through the eyes, and directly, through the skull. The hypothalamus of the bird brain contains special cells that are sensitive to extremely low light levels, intensities comparable to the amount of light that can penetrate brain tissue (Akins and Burns 2001).
http://people.eku.edu/ritchisong/avianreproduction.html
Testosterone increases availability of carotenoids -- Androgens and carotenoids play a fundamental role in the expression of secondary sex traits in animals that communicate information on individual quality. In birds, androgens regulate song, aggression, and a variety of sexual ornaments and displays, whereas carotenoids are responsible for the red, yellow, and orange colors of the integument. Parallel, but independent, research lines suggest that the evolutionary stability of each signaling system stems from tradeoffs with immune function: androgens can be immunosuppressive, and carotenoids diverted to coloration prevent their use as immunostimulants. Despite strong similarities in the patterns of sex, age and seasonal variation, social function, and proximate control, there has been little success at integrating potential links between the two signaling systems. These parallel patterns led us to hypothesize that testosterone increases the bioavailability of circulating carotenoids. To test this hypothesis, Blas et al. (2006) manipulated testosterone levels of Red-legged Partridges (Alectoris rufa) while monitoring carotenoids, color, and immune function. Testosterone treatment increased the concentration of carotenoids in plasma and liver by >20%. Plasma carotenoids were in turn responsible for individual differences in coloration and immune response. These results provide experimental evidence for a link between testosterone levels and immunoenhancing carotenoids that (i) reconciles conflicting evidence for the immunosuppressive nature of androgens, (ii) provides physiological grounds for a connection between two of the main signaling systems in animals, (iii) explains how these signaling systems can be evolutionary stable and honest, and (iv) may explain the high prevalence of sexual dimorphism in carotenoid-based coloration in animals.
http://people.eku.edu/ritchisong/avianreproduction.html
sperm are stored at the terminal end of the 
deferens (seminal glomus), and this creates a swelling called the cloacal protuberance
Male birds have paired abdominal testes lying cranioventral to the first kidney lobe. Testes increase dramatically in size during the breeding season. The
deferens emerges medially and passes caudally to the cloaca where it has a common opening with the ureter in the Urodeum. The terminal
deferens is swollen as a storage organ: the seminal glomus (or seminal vesicle as in the drawing to the right).
As in mammals, sperm formation is temperature sensitive, and maturation is assisted by nocturnal drops in temperature, or by the development of scrotal-like external thermoregulatory swellings holding the seminal glomera.
In addition, male birds tend to have relatively low extragonadal sperm reserves and sperm are ejaculated soon after production in the testes.
http://people.eku.edu/ritchisong/avianreproduction.htmlEgg production * Most birds have only one ovary and one oviduct. In early stages of embryonic development, each female bird has two ovaries; only the left one develops into a functional organ. In some birds, such as hawks, the right ovary and oviduct usually develop. A mature ovary looks like a cluster of grapes. and may contain up to 4,000 small ova which can develop into mature ova.
* With fertilization, the ovum (egg) becomes a developing embryo
* The embryo passes through the oviduct; typically takes about 24 hours (for passerines & most other birds)
* The demand for calcium to make the egg shell is very high, and so the circulating levels of blood calcium in birds are greatly elevated compared to mammals, typically twice as much.
A must see sitehttp://people.eku.edu/ritchisong/avianreproduction.htmlhttp://people.eku.edu/ritchisong/birdnests.htmlhttp://people.eku.edu/ritchisong/avianreproduction2.html
BrokenWing
