Environmental and hormonal factors in seasonal breeding in free-living male Indian rose-ringed parakeets (Psittacula krameri).

Seasonal changes in testicular activity, plasma luteinizing hormone (LH), estradiol (E2), testosterone (T), and 5 alpha-dihydrotestosterone (5 alpha-DHT) were related to pair bond formation, nest building, nest defense, and parental behavior in free-living Indian rose-ringed parakeets (Psittacula krameri) in northwest India. Spermatozoa production occurred between January and March when daylengths were short (10-12 hr) and ambient temperature was seasonally low (8-20 degrees C). At other times of the year the testes were regressed. Plasma LH levels increased during the prebreeding period (September-December) when the birds were forming pairs and selecting or defending nest sites. Plasma LH levels increased further between January and March and decreased to seasonal low values during the post breeding period between April and June when the birds were caring for young. Concentrations of plasma androgens and estrogens were similar during the prebreeding and postbreeding phases of the breeding cycle. During the breeding period, the ratios between plasma 5 alpha-DHT and testosterone and between plasma estradiol and testosterone increased. It is proposed that the absence of marked seasonal changes in plasma steroid levels is related to nest defense behavior which occurs during the prebreeding, breeding, and postbreeding phases of the breeding cycle. Winter breeding makes it possible for the parakeets to avoid competition with other birds for nesting sites, to avoid fledging young during the monsoon period, and to take advantage of the winter pea crop which provides the female with extra nutrients for egg production.