SUMMARYThe timing and duration of gonadal phases in the year indicates that breeding cycles are regulated by endogenous mechanisms. The present study on tropical spotted munia (Lonchura punctulata) investigates whether such mechanisms are based on circannual rhythms, and whether circannual rhythms between sexes differ in their relationship with the light environment. Birds were subjected to 12h light per day (12L:12D), alternate days of light and darkness (24L:24D, LL/DD) and continuous light (LL), with L22lx and D≤1lx, for 28months at constant temperature (18±1°C). Groups kept on natural day lengths (NDL) served as controls. Measurement of body mass, gonads and molts of the primary wing feathers and body plumage at regular intervals showed that birds underwent repeated cycles in gonads and molt, but not in body mass. Under NDL, gonadal phases in both sexes cycled with 12month periods. Under other conditions, males cycled with similar periods of ~11months, but females cycled with relatively large period variations, ~10-13months. Gonadal recrudescence-regression phase was longer in males than in females and, in both sexes, longer in the second year compared with the first year. The molt of wing primaries was more closely coupled to gonadal maturation in groups on NDL and 12L:12D than in groups on LL and LL/DD, but this relationship drifted apart in the second year. Body plumage molts were relatively more highly variable in both frequency and pattern in females than in males. It is suggested that annual breeding cycle in spotted munia is regulated by the self-sustained circannual rhythms, which probably interact with the annual photoperiodic cycle to synchronize breeding cycles to calendar year. Both sexes seem to have independent timing strategies, but females appear to share a greater role in defining the reproductive season in relation with the environment. Supplementary material available online at

SUMMARY In a seasonally breeding bird species, food deprivation affects reproduction. A key question is whether food shortage at any time in the year will affect reproduction even though the food supply subsequently becomes adequate. A prediction would be that a food supply that is of shorter duration than that optimally required during a life-history stage will have consequential effects on the succeeding life-history stages. Two experiments investigated this in gonadally regressed migratory Red-headed Buntings(Emberiza bruniceps) at two life-history stages: photosensitive and photorefractory. Experiment 1 employed two groups of photosensitive birds, and experiment 2 employed two groups of photorefractory birds. In both the experiments, birds were exposed for 8 weeks to a neutral day length at dim light intensity (12 h light: 12 h darkness, 12L:12D; L=∼5 lux, D=0 lux)with restricted feeding regimes (6 h food present: 18 h food absent, P:A 6:18 or P:A 12:12) and subsequently maintained for another 13 weeks at a highly stimulatory day length (16L:8D; L=400 lux; D=0 lux) with food ad libitum. We report that the pretreatment with restricted food cycles influenced the subsequent photoperiodic induction of reproductive (testis growth and molt) but not of metabolic (body fattening and mass gain)functions. The testicular response cycle under 16L:8D had a significantly lower amplitude in birds pretreated with P:A 6:18 than with P:A 12:12. Similarly, the recovery of photosensitivity was slower in photorefractory birds pretreated with P:A 6:18 than with P:A 12:12 food cycles. Overall, our findings show for the first time in a seasonally breeding vertebrate species that food deprivation during non-breeding periods of the annual cycle can affect reproductive functions later in the year.

Circannual rhythms regulate seasonal reproduction in many vertebrates. The present study investigated whether circannual reproductive phenotypes (rhythms in growth of gonads and molt) were generated independently of the circadian clocks in the subtropical non-photoperiodic spotted munia (Lonchura punctulata). Birds were subjected to light:dark (LD) cycles with identical light but varying dark hours, such that the period of LD cycle (T) equaled 16 h (T16; 12 h L:4 h D), 21 h (T21; 12 h L:9 h D), 24 h (T24; 12 h L:12 h D) and 27 h (T27; 12 h L:15 h D), or to continuous light (LL, 24 h L:0 h D) at ~18°C. During the~21 month exposure, munia underwent at least two cycles of gonadal development and molt; changes in body mass were not rhythmic. This was similar to the occurrence of annual cycles in reproduction and molt observed in wild birds. A greater asynchrony between circannual cycles of gonad development and molt indicated their independent regulation. Females showed reproductive rhythms with similar circannual periods, whilst in males, circannual periods measured between peak gonadal size were longer in T21 and T24 than in T16 or T27. This suggested a sex-dependent timing of annual reproduction in the spotted munia. Also, food availability periods may not influence the circannual timing of reproduction, as shown by the results on the rhythm in gonadal growth and regression in munia under T-photocycles and LL that provided differential light (feeding) hours. Further, a short-term experiment revealed that activity-rest patterns in munia were synchronized with T-photocycles, but were arrhythmic under LL. We conclude that circadian rhythms are not involved in the timing of the annual reproductive cycle in the spotted munia.

We investigated the effects of temperature on photoperiodic induction of the phenologies linked with migration (body fattening and premigratory night-time restlessness, Zugunruhe) and reproduction (testicular maturation) in the migratory blackheaded bunting. Birds were exposed for four weeks to nearthreshold photoperiods required to induce testicular growth (11.5 L:12.5 D and 12 L:12 D) or for 18 weeks to a long photoperiod (13 L:11 D) at 228C or 278C (low) and 358C or 408C (high) temperatures. A significant body fattening and half-maximal testicular growth occurred in birds under the 12 L, but not under the 11.5 L photoperiod. Further, one of six birds in both temperature groups on 11.5 L, and four and two of six birds, respectively, in low-and high-temperature groups on 12 L showed the Zugunruhe. Buntings on 13 L in both temperature groups showed complete growth-regression cycles in body fattening, Zugunruhe and testis maturation. In birds on 13 L, high temperature attenuated activity levels, delayed onset of Zugunruhe by about 12 days, reduced body fattening and slowed testicular maturation. The effect of temperature seems to be on the rate of photoperiodic induction rather than on the critical day length. It is suggested that a change in temperature could alter the timing of the development of phenologies linked with seasonal migration and reproduction in migratory songbirds.

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