Environmental, dietary, and hormonal factors in the regulation of seasonal breeding in free-living female Indian rose-ringed parakeets ( Psittacula krameri)

Abstract

The roles of environmental, dietary, and hormonal factors in the timing of seasonal breeding were assessed in free-living female Indian rose-ringed parakeets, Psittacula krameri, in northwest India (22 ° 2′N, 73 °E). The ovaries and oviducts began to enlarge in January, were fully developed in February, and began to regress in March. During this time there was no significant change in the concentration of plasma luteinizing hormone (LH) or estradiol. The concentration of plasma LH decreased ( P < 0.01) at the end of the breeding season. Pair bond formation occurred between September and December and was associated with an increase in levels of plasma LH but no change in plasma estradiol. Concentrations of plasma testosterone (T) and 5α-dihydrotestosterone (5α-DHT) did not vary significantly during the year and were similar to those in males except for higher values of 5α-DHT and lower values of T during the pre- and postbreeding periods, respectively. The similar levels of plasma androgens in both sexes may be related to the equal roles that both sexes play in the defence of their nest holes. An analysis of crop sac contents showed that the birds fed chiefly on pigeon peas ( Cajanus cajan) during the breeding season and on cereal grains at other times of the year. It is suggested that pigeon peas provide the extra nutrients, including calcium, required for egg production. Since pigeon peas ripen between November and March, the production of the crop may play a role in the timing of seasonal breeding. A further factor appears to be competition for nest sites. By breeding in winter, the parakeet avoids competing with other species which nest in holes.