Avian Breeding, Ovulation and Oviposition - Anatomy & Physiology

Breeding Cycles

Classified according to length of cycle and the time of year when the species becomes reproductively active.
- Continuous breeders are reproductively active throughout the year e.g. Khaki Campbell duck.
- Most wild species that breed in temperate, subarctic and arctic zones display yearly cycles.
Tropical or desert species may breed with cycles less than a year, at 6-month intervals or when conditions are favourable (opportunistic breeders).

Usually lay one or more eggs in a clutch and terminate laying to incubate the eggs.
Number of eggs per clutch and total number of clutches vary with species and season.

In females, FSH is mainly responsible for follicular growth.
Developing follicles produce Oestrogen from Theca and interstitial cells and Progesterone from Granulosa cells.
Increasing levels of Oestrogen stimulate an LH surge to cause the follicle to split and release the primary oocyte.
Oestrogen mobilizes calcium from the bone, increasing plasma concentrations for egg formation.
Progesterone secretion continues to inhibit further ovulation and stimulate behavioural changes associated with broodiness and incubation.
Prolactin stimulates the production of crop milk in male and female columbiformes.
Oviposition is controlled by prostaglandins and Arginine Vasotocin.

Number of ovulations varies with species, mostly lay one clutch a year.
Infundibulum catches the oocyte, facillitated by the left abdominal air sac which tightly encloses the ovary.
Once ovulation has taken place, the follicle shrinks and regresses.
No corpus luteum remains, as there is no developing embryo to maintain.

Expulsion of the egg
Contraction of the Uterine shell gland (Vagina) with relaxation of abdominal muscles.
Minutes to hours
- Cuckoos lay their eggs in seconds so they can get away before the host returns.