Circadian rhythms of oviposition and feeding activity in Japanese quail: effects of cyclic administration of melatonin

The aim of these experiments was to test the effect of a cyclic administration of melatonin, by mimicking the daily rhythm of hormone levels, on the circadian organization of two distinct functions in quail: oviposition and feeding activity. Laying and feeding rhythms under photoperiodic conditions and constant darkness (DD) were investigated. Under DD, where the two rhythms were free running, a daily rhythm of melatonin was administered. In LD 14h:10h, two different individual profiles of laying were established, with stable females laying at the same time each day and delayed females laying progressively later each day. For feeding activity, all birds were clearly synchronized to the photoperiodic cycle. In DD, the laying birds showed a free-running rhythm of oviposition with a period longer than 24 h for both profiles but the delayed profile females had a longer period than stable profile females. In comparison, the free-running period of feeding rhythm of the same birds was shorter than 24 h. A cyclic administration of melatonin had no effect on laying rhythm, which continued to free-run in DD, whereas feeding activity was synchronized as soon as the first cycle of melatonin was administered. From these results, it seems that two different circadian systems drive each of the two types of behavior separately. Melatonin could be the main synchronizer for the temporal control of feeding behavior, but it does not play a part in the control of oviposition in Japanese quail.     

Daily organization of laying in Japanese and European quail: effect of domestication

In the present study, we aimed to examine the possible effects of domestication on the daily organization of laying in female quail. To achieve this we compared laying patterns in a laboratory strain of Japanese quail with those in European quail originating from a wild population. Under LD 14:10, the same specific laying window was observed, with ovipositions occurring mainly between 7 h and 15 h after lights on. Thus, domestication did not modify the specific daily organization of laying in females laying in the afternoon. Research about the functional value of this temporal organization in the field thus seems justified. At an individual level, two distinct laying profiles were recorded, as in a previous experiment on an industrial Japanese quail strain selected for meat and egg production. However, different frequencies were noted. Whereas stable profile females (laying at the same time each day) were predominant (80.4%, N=102) in the industrial Japanese quail strain, delayed profile females (laying successively later each day) appeared dominant in the European quail (81%, N=22). The Japanese quail from the laboratory strain constituted an intermediate group with a slight dominance of the stable profile (58.8%, N=17). Thus, domestication has changed the frequencies of the laying profiles, favoring stable females, which are the most productive birds. A model involving interaction between one circadian rhythm and one ultradian rhythm can explain the observed laying profiles.     

Circadian rhythm of activity during the annual phases in the European quail, Coturnix coturnix

Migratory birds, such as the European quail, present an annual cycle with the following phases: moult, fattening, migration and reproduction. This study aimed at determining how variations in the circadian rhythm of feeding during the annual cycle took endogenous rhythmic characteristics into account. The birds (n = 8) were maintained under constant dim light from the age of 1 to 9 months. Feeding activity was recorded using infra-red detectors. The birds expressed all the phases, except migration. Activity was arrhythmic when they were moulting. A circadian rhythm of feeding activity appeared during the fattening phase. In males, the circadian period lengthened and the clarity of the rhythm increased during sexual development. These results appear to confirm the effects of physiological state on the temporal organisation of activity. Variations of the circadian rhythm could influence the ability to synchronize with exogenous cycles such as the alternation of day and night.     

Effect of Light Intensity on Circadian Activity in Developing Japanese Quail

The effects of constant light on the expression of the circadian rhythm of feeding activity in Japanese quail, and in particular on the clarity of the rhythm were investigated. We used 46 4-week-old birds (35 females and 11 males) issued from two lines selected for a more (line R: 25 females and 10 males) or less (line A: 10 females and 1 male) clear circadian rhythm of feeding activity. The birds, were placed successively under three light schedules: constant darkness (DD), constant dim green light (LLdim) and constant bright light (LLbright). Schedules were changed every 2 weeks. Feeding activity was recorded continuously, analysed by autocorrelation and spectral analysis, and the ratio of the correlation coefficients and the area of the spectrum peak were used as indexes to quantify the clarity of the circadian rhythm. During the experiment, some birds showed gonadal development. Therefore, we analysed separately birds showing either a high or low degree of sexual development at the end of the experiment. In DD, 35 birds showed a circadian feeding rhythm with a mean period of 22.5 ± 0.1 h, whereas 11 birds showed an arrhythmic activity. In LLdim, 27 birds were rhythmic (22 birds R and 5 birds A), and in LLbright, only 3 birds showed a rhythmic circadian activity. For the R-line birds (for females and males), the rhythm clarity decreased in LLdim compared to DD, except for the not developed females. For the A-line birds (for females), the rhythm clarity of the immature birds increased in LLdim and that of the developed birds remained stable. In LLbright, circadian activity became arrhythmic. In LLdim, the active phases of 12 birds showed two main peaks, with mean periods of 22.7 h and 25.1 h, respectively. Therefore, constant light appeared to have an inhibitory effect on the expression of the circadian rhythm. We postulate that two hierarchically coupled oscillators could control circadian feeding activity, and arrhythmia in LLbright could be the results of internal desynchronization of the pacemakers.     

Effect of Light Intensity on Circadian Activity in Developing Japanese Quail

The effects of constant light on the expression of the circadian rhythm of feeding activity in Japanese quail, and in particular on the clarity of the rhythm were investigated. We used 46 4-week-old birds (35 females and 11 males) issued from two lines selected for a more (line R: 25 females and 10 males) or less (line A: 10 females and 1 male) clear circadian rhythm of feeding activity. The birds, were placed successively under three light schedules: constant darkness (DD), constant dim green light (LLdim) and constant bright light (LLbright). Schedules were changed every 2 weeks. Feeding activity was recorded continuously, analysed by autocorrelation and spectral analysis, and the ratio of the correlation coefficients and the area of the spectrum peak were used as indexes to quantify the clarity of the circadian rhythm. During the experiment, some birds showed gonadal development. Therefore, we analysed separately birds showing either a high or low degree of sexual development at the end of the experiment. In DD, 35 birds showed a circadian feeding rhythm with a mean period of 22.5 ± 0.1 h, whereas 11 birds showed an arrhythmic activity. In LLdim, 27 birds were rhythmic (22 birds R and 5 birds A), and in LLbright, only 3 birds showed a rhythmic circadian activity. For the R-line birds (for females and males), the rhythm clarity decreased in LLdim compared to DD, except for the not developed females. For the A-line birds (for females), the rhythm clarity of the immature birds increased in LLdim and that of the developed birds remained stable. In LLbright, circadian activity became arrhythmic. In LLdim, the active phases of 12 birds showed two main peaks, with mean periods of 22.7 h and 25.1 h, respectively. Therefore, constant light appeared to have an inhibitory effect on the expression of the circadian rhythm. We postulate that two hierarchically coupled oscillators could control circadian feeding activity, and arrhythmia in LLbright could be the results of internal desynchronization of the pacemakers.     

Cyclic melatonin synchronizes the circadian rhythm of feeding activity in Japanese quail,Coturnix c. japonica

In Japanese quail, we can observe the circadian rhythm of feeding activity in constant conditions, especially in birds from selected lines. In order to try to test the importance of melatonin as hormonal output for the circadian system, we gave a 24-h period cycle of exogenous melatonin to some of these birds when they were free running. We used castrated males firstly in order to cancel the known effect of steroids on circadian organisation. Secondly, as castrated birds generally expressed a very short periodicity, it allowed us to check induced synchronisation more easily. We maintained ten castrated males in constant dim light. We divided the experiment into five successive phases. The birds received a 24-h period cycle of melatonin (M phase) or of control solution with only the alcoholic solvent (C phase) as a drink. Before and after each one of these two phases, we gave water continually to drink (W1, W2 and W3 phases). Thus, the successive phases were W1-M-W2-C-W3. We measured intake of liquids and plasma melatonin concentrations to check melatonin ingestion. We automatically recorded individual feeding activity by infrared detectors, and analysed this by spectral analysis. At the beginning of the experiment, eight birds showed a rhythmic feeding activity, with a mean period of 22.9 +/- 0.2 h, and the two others an arrhythmic circadian activity. During the 24-h period cycle of exogenous melatonin, for the rhythmic birds, the circadian period became approximately 24 h (23.9 +/- 0.2 h), the inactive phase corresponding to the period of melatonin availability. During the W2 and C phases, the circadian period was similar to that expressed during the W1 phase. Moreover, when birds only drink water, we found a significant positive relationship between the clarity of the circadian rhythm and the ratio, between the melatonin level of the inactive phase and that of the active phase. These facts support the hypothesis of the role of this hormone in the regulation of the circadian system, at least for feeding activity, in quail.     

The quail's eye: a biological clock

The site (intraocular vs. extraocular) of the biological clock driving a rhythm in melatonin content in the eyes of Japanese quail was investigated by alternately patching the left and right eyes of individual birds, otherwise held in constant light, for 12-hr periods. This patching protocol, therefore, exposed each eye to a light-dark cycle (LD 12:12) 180 degrees (12 hr) out of phase with the LD cycle experienced by the other eye. The optic nerves to both eyes were transected prior to initiating the patching protocol. The ocular melatonin rhythm (OMR) of the left eyes of quail could be entrained by this procedure 180 degrees out of phase with the rhythm expressed by the right eyes. Since optic nerve section would have deprived any putative extraocular clocks of photic entrainment information, the results show conclusively that the clock driving the OMR is located within the eye itself. In addition, the OMR of Japanese quail is remarkably unaffected by removing two potential neural inputs to the eye (sympathetic innervation from the superior cervical ganglia, and input from the isthmo-optic nucleus of the midbrain); this suggests that these inputs are not required to maintain the OMR. Finally, the clock driving the OMR of one eye does not appear to be coupled to the clock driving the OMR in the other eye, since permanently patching one eye abolished the ability of the patched eye to re-entrain to an 8-hr shift in the phase of an LD 12:12 cycle, whereas the exposed eye rapidly re-entrained to the phase-shifted cycle.     

Does a biological clock reside in the eye of quail?

The site (intra- vs. extraocular) of the circadian clock driving an ocular melatonin rhythm in Japanese quail was investigated by alternately covering the left and right eyes of individual quail, otherwise held in constant light (LL), for 12-hr periods. This procedure exposed each eye to a light-dark (LD) 12:12 light cycle 180 degrees (12 hr) out of phase with the LD 12:12 light cycle experienced by the other eye. This protocol entrained the melatonin rhythm in the left eye of quail 180 degrees out of phase with the rhythm expressed in the right eye. These results are compatible with the hypothesis that an independent light-entrainable circadian pacemaker resides in each eye; they are incompatible with the hypothesis that a single (or functionally single) extraocular pacemaker drives the ocular melatonin rhythm in both eyes. However, the results are also compatible with a model in which two independent extraocular circadian pacemakers, each with an exclusive photic input from one eye, drive the ocular melatonin rhythm.     

Melatonin does not link the eyes to the rest of the circadian system in quail: a neural pathway is involved

Blinding by enucleation has a dramatic effect on the circadian activity rhythm of Japanese quail. The activity patterns of enucleated birds held under 24-hr light-dark cycles are disrupted, although entrainment can persist in many birds. In constant darkness (DD), blinded birds are rendered arrhythmic. These results demonstrate that the eyes are a major component of the circadian system, and that insofar as enucleation produces arrhythmicity in DD, the eyes' role is not merely a photosensory one. The eyes of quail can synthesize and secrete the hormone melatonin, which has been implicated as a blood-borne messenger relaying timing information between elements of the circadian system in some avian species. However, the way in which the eyes communicate with the rest of the circadian system in quail appears to be neural, since (1) optic nerve section produces the same effects as blinding by enucleation on the circadian activity rhythm, and (2) eyes subjected to optic nerve section retain their ability to synthesize and secrete melatonin.     

Difference of social motivation in quail selected for divergent circadian activity

Endogenous rhythms are adaptive responses to predictable changes of the environment, like the day/night cycle. Some researches demonstrated that social cycles can influence the circadian rhythm, while no study investigated the effect of endogenous rhythmicity on the sociability in Vertebrates. This study investigated whether differences in the functioning of the circadian system was associated with social motivation in Japanese quail (Coturnix c. japonica).We compared quail from a line expressing a robust circadian rhythm of feeding activity (R) to quail from a line expressing circadian arrhythmicity of feeding activity (A) under constant darkness. Classic behavioral tests evaluated social motivation of these birds.When socially isolated, the motivation of R quail to re-establish contact with conspecifics appeared stronger than that of A quail. When in the presence of conspecifics, R quail faced a stressful situation (change of environment) more calmly than did A quail. Thus, variation of circadian behavioral rhythmicity is associated with variation in social motivation in Japanese quail. Rhythmic animals appeared to respond more appropriately to environmental challenges than arrhythmic animals.     

The circadian rhythm of thermoregulation in Japanese quail

Japanese quail exhibit a robust circadian rhythm in body temperature. This rhythm is readily entrainable by 24 h light-dark (LD) cycles and persists under constant conditions. Because both the pineal organ and the eyes have been implicated as major components of the circadian system of birds, the role of these organs in generating the rhythm of body temperature was investigated. Pinealectomy, when performed alone, had little effect on the body temperature rhythm of quail either under LD or under constant darkness (DD). Most birds subjected to optic nerve section alone remained rhythmic in DD although the robustness of the rhythm was decreased, and 25% became arrhythmic. Birds subjected to both pinealectomy and optic nerve section behaved similarly to birds subjected to optic nerve section alone. However, complete eye removal, when performed alone or in combination with pinealectomy, caused all birds to become arrhythmic in DD. The data support the hypothesis that the eyes are the loci of circadian pacemakers in quail that act, via both neural and hormonal outputs, to preserve the integrity of (self-sustaining or damped) circadian oscillators located elsewhere.     

Daily temporal organization of laying in Japanese quail: variability and heritability

In birds, many behavioral and physiological processes that occur during reproduction show daily rhythms in response to environmental temporal constraints. In this study, the individual daily organization of laying and its genetic determinant in Japanese quail (Coturnix coturnix japonica) were analyzed. For this purpose, the oviposition time of 102 randomly chosen females, maintained in long-day photoperiodic conditions (LD 14h:10h) for 1 mon was observed and extreme phenotypes selected. Laying is characterized by two parameters: oviposition interval and laying hour.

The birds showed a specific time of laying during 24 h. All eggs were laid in the afternoon between 6.5 and 14 h after lights on (HALO). Two laying profiles were determined: 20% of females with an oviposition interval greater than 24 h (24.7±0.2 h) (the “delayed” profile) laid progressively later each day until a pause day. The remaining 80% of the females laid at the same time each day, with few pause days and an oviposition interval close to 24 h (24.0±0.2 h) (the “stable” profile). Among the females, showing this last profile, an intra-individual stability and an inter-individual variability of laying hour was established. Two extreme laying phenotypes were then determined: the “early” phenotype (E) for females laying on average between 7.5 and 9.5 HALO and the “late” phenotype (L) for females laying between 12.5 and 14 HALO.

In order to study the genetic basis of the laying hour, three females of each extreme phenotype were selected and crossed with two different males. The E and L females produced 57 F1E and 42 F1L daughters, respectively. F1 females displayed both laying profiles. However, the proportion of females displaying a “delayed” profile was higher in the L line (50%) than in the E line (29.8%). For the “stable” daughters, artificial selection induced an advance in laying hour of 4.7% for the E line and a delay of 4.7% for the L line. Realized heritability was estimated at 0.5. Moreover, the laying hour of the daughters was correlated positively to that of the mothers (N=61;r=0.45). These results support the notion of heritability of oviposition time in Japanese quail.     

Effect of photoperiods on feed intake rhythms of domestic fowl

Pinealectomized and control groups of Single Comb White Leghorn pullets were housed in individual laying cages within an experimental room maintained at a temperature of 22 ± 2°C. Hourly feed intake data were collected on the birds subjected to single 3-h changes in the duration of light or dark periods at either auroral (lights-on) or vespertine (lights-off) time of a 14L:10D lighting cycle. Feed intake reached an acrophase at either the 12th or 13th hour of the light period then declined until the onset of darkness. Vespertine changes in the light cycle were more effective in shifting the intake acrophase than the auroral changes. This observation was consistent irrespective of the direction of the change. When the laying hens were subjected to a 26-h lighting rhythm, the strength of cyclic light as a zeitgeber for feed intake rhythm was again demonstrated. The feed intake rhythm developed a 26-h duration with an acrophase consistently 22–23 hours post-vespertine. Pinealectomy did not effect the ability of hens to adjust to new lighting regimens.     

Daily laying time in free-living European starlings: solar noon, a potential synchronizer

Reproduction is generally controlled by important temporal constraints involving complex adaptive mechanisms. Birds, in temperate zones, present marked breeding seasonality as well as marked daily organization of reproductive behavior, especially laying. Intra-specific variability and determinants of this pattern have been investigated mainly in domestic non-passerine birds. The present study analyzed the daily temporal organization of laying in a free-living species, the European starling, Sturnus vulgaris. Breeding in a starling colony was monitored for five consecutive years using a non-invasive method (infrared video camera) to precisely estimate laying times. European starlings present a marked daily laying rhythm, ovipositions occurring only during a morning species-specific temporal window. Inside this laying window, time intervals between successive eggs varied greatly among females. Contrary to many species, the light/dark cycle did not appear to control laying time in European starlings, but daily variations of the ultraviolet composition of the solar spectrum appeared to be a possible Zeitgeber of this behavior.     

Daily temporal organization of laying in Japanese quail: variability and heritability

In birds, many behavioral and physiological processes that occur during reproduction show daily rhythms in response to environmental temporal constraints. In this study, the individual daily organization of laying and its genetic determinant in Japanese quail (Coturnix coturnix japonica) were analyzed. For this purpose, the oviposition time of 102 randomly chosen females, maintained in long-day photoperiodic conditions (LD 14h:10h) for 1 mon was observed and extreme phenotypes selected. Laying is characterized by two parameters: oviposition interval and laying hour.

The birds showed a specific time of laying during 24 h. All eggs were laid in the afternoon between 6.5 and 14 h after lights on (HALO). Two laying profiles were determined: 20% of females with an oviposition interval greater than 24 h (24.7±0.2 h) (the “delayed” profile) laid progressively later each day until a pause day. The remaining 80% of the females laid at the same time each day, with few pause days and an oviposition interval close to 24 h (24.0±0.2 h) (the “stable” profile). Among the females, showing this last profile, an intra-individual stability and an inter-individual variability of laying hour was established. Two extreme laying phenotypes were then determined: the “early” phenotype (E) for females laying on average between 7.5 and 9.5 HALO and the “late” phenotype (L) for females laying between 12.5 and 14 HALO.

In order to study the genetic basis of the laying hour, three females of each extreme phenotype were selected and crossed with two different males. The E and L females produced 57 F1E and 42 F1L daughters, respectively. F1 females displayed both laying profiles. However, the proportion of females displaying a “delayed” profile was higher in the L line (50%) than in the E line (29.8%). For the “stable” daughters, artificial selection induced an advance in laying hour of 4.7% for the E line and a delay of 4.7% for the L line. Realized heritability was estimated at 0.5. Moreover, the laying hour of the daughters was correlated positively to that of the mothers (N=61;r=0.45). These results support the notion of heritability of oviposition time in Japanese quail.     

Daily Laying Time in Free‐Living European Starlings: Solar Noon,a Potential Synchronizer

Reproduction is generally controlled by important temporal constraints involving complex adaptive mechanisms. Birds, in temperate zones, present marked breeding seasonality as well as marked daily organization of reproductive behavior, especially laying. Intra‐specific variability and determinants of this pattern have been investigated mainly in domestic non‐passerine birds. The present study analyzed the daily temporal organization of laying in a free‐living species, the European starling, Sturnus vulgaris. Breeding in a starling colony was monitored for five consecutive years using a non‐invasive method (infrared video camera) to precisely estimate laying times. European starlings present a marked daily laying rhythm, ovipositions occurring only during a morning species‐specific temporal window. Inside this laying window, time intervals between successive eggs varied greatly among females. Contrary to many species, the light/dark cycle did not appear to control laying time in European starlings, but daily variations of the ultraviolet composition of the solar spectrum appeared to be a possible Zeitgeber of this behavior.     

The photoperiodic entrainment and induction of the circadian clock regulating seasonal responses in the migratory blackheaded bunting (Emberiza melanocephala)

The properties of the circadian photoperiodic oscillator have been investigated in detail only in the Japanese quail. While the study of the quail is clearly very important, one cannot simply assume that other species, especially passerines that seem to have a different circadian organization than quail, function the same way. The current set of experiments was conducted to understand the entrainment and photoinduction of the circadian photoperiodic oscillator in a passerine species, the blackheaded bunting (Emberiza melanocephala). The experimental paradigm used skeleton photoperiods with two light periods, the first called the “entraining light pulse” (E-pulse) and the second called the “inducing light pulse” (I-pulse). Three experiments were performed on photosensitive male birds (N=6-8/group). Experiment 1 investigated the effects of the temporal relationship between E- and I-pulses on photoperiodic induction. Buntings entrained to 8h:16h L:D for 4 wk were released into constant dim light (LL_dim, ∼1 lux). Beginning on subjective day 8, they received for 8 wk, E- and I-pulses only at alternate cycles. While I-pulse was 1 h and always began at zt 11.5, E-pulse varied in duration and timing (the 1h E-pulse beginning either at zt 0, zt 5, or zt 9, the 4h one beginning at zt 0 or zt 6, and the 10h one at zt 0; zeitgeber time 0=time of lights-on under 8h:16h L:D prior to release into LL_dim). A photoperiodic response was induced only when the E-pulse began at zt 0, and thus the beginning of E- and I-pulses were separated by 11.5 h. Experiment 2 determined whether the duration of the E-pulse influences the position of the photoinducible phase (φi) of the circadian photoperiodic oscillator. Birds were entrained to 1h:23h L:D or 10h:14h L:D for 2 wk, and then exposed to 1h I-pulse at zt 11.5, zt 15, or zt 18.5 for another 8 wk. Photoperiodic induction occurred at all 3 zts in birds entrained to 10 h but only at zt 11.5 in birds entrained to 1 h, which infers the circadian rhythm of photoinducibility (CRP) in buntings was re-entrained when I-pulse fell at zt 15 and after. The last experiment examined the possibility of the re-entrainment of the CRP to light pulses falling at zt 15 and after. Birds received 1h I-pulse for 8 wk at zt 15 following 2 wk of 2.5h:21.5h L:D or 3.5h:20.5h L:D, or at zt 21.5 or zt 22.5 following 2 wk of 10h:14h LD. Photoperiodic induction was consistent with the hypothesis of the re-entrainment of the CRP under these light-dark cycles. The I-pulse appeared to be interpreted as a “new dawn”, and so the photoperiodic induction was determined by the coincidence of φi with the E-pulse. These results suggest a phase-dependent action of light on the circadian oscillator regulating photoperiodic responses in the blackheaded bunting. This could be a useful strategy for a photoperiodic species to regulate its seasonal responses in nature.     

Circadian and seasonal responses in Indian weaver bird: subjective interpretation of day and night depends upon both light intensity and contrast between illuminations

This study investigated whether changes in illumination modify perception of day and night conditions in a diurnal species, the Indian weaver bird. Birds were initially subjected to a 12-h light:12-h dark regime (12L:12D; L=20 lux, D =0.5 lux). After every 2 wks, the combinations of light illumination in L and D phases were changed as follows: 20:2 lux, 20:5 lux, 20:10 lux, 20:20 lux, 20:100 lux, and 20:200 lux. Finally, birds were released into dim constant light (0.5 lux) for 2 wks to determine the phase and period of the circadian activity rhythm. They were also laparotomized at periodic intervals to examine the effects of the light regimes on the seasonal testicular cycle. All individuals showed a consistently similar response. As evident by the activity pattern under these light regimes, both in total activity during contrasting light phases and during the 2?h in the beginning and end of first light phase, birds interpreted the period of higher light intensity as day, and the period of lower intensity as the night. During the period of similar light intensity, i.e., under LL, birds free-ran with a circadian period ( ~ 24 h). In bright LL (20 lux), the activity rhythm was less distinct, but periodogram analysis revealed the circadian period for the group as 24.46 (+/-) 0.41 h (mean???SE). However, in dim LL at the end of the experiment, all birds exhibited a circadian pattern with average period of 25.52 (+/-) 0.70 h. All birds also showed testicular growth and regression during the 16-wks study. It is suggested that weaver birds interpret day and night subjectively based on both the light intensity and contrast between illuminations during two phases over the 24 h.     

Annual cycles of migratory fattening, reproduction and moult in European quail (Coturnix coturnix)

Experimental studies of the physiological mechanisms underlying avian migration have concentrated on small passerines. The present study is concerned with the regulation of migratory fat deposition in a galliform. the European quail (Coturnix coturnix). The increased mass associated with migration was due exclusively to the deposition of fat whereas the increased body mass of laying females was due to increases in lean tissue and water as well as fat. Annual cycles of body mass, moult, gonadal size and plasma luteinizing hormone were measured every other week in captive males and females held outdoors under natural daylengths and temperatures in Bristol, UK (51° 27' N). Males and females showed two peaks of fat deposition each year which occurred at the migratory passage times reported in wild birds. Luteinizing hormone levels and gonadal size increased in parallel with vernal fat deposition, and remained high until late summer. The pattern of primary feather moult in the intact birds was similar to that of wild quail, with moult following gonadal regression and being suspended during autumnal fattening. Castration of European quail did not inhibit the expression of migratory fattening, as it does In certain passerines. In fact, castrates displayed fattening cycles that were more clearly defined and of greater amplitude than those in the intact males. The annual cycle of European quail differs from that of other well-studied passerine migrants such as Zonotrichia sparrows, and this is most likely associated with differences in breeding ecology. In addition, the ability of quail to express vernal fattening independently of the presence of the gonads suggests that taxonomic differences between migratory species are also apparent in the physiological mechanisms of migratory fattening.     

Effect of the Ageing on the Circadian Activity in Selected Japanese Quail

Our aim was to study the age-related changes of the rhythm of feeding activity in sexually inactive Japanese quail, Coturnix japonica . For that, we recorded the feeding activity of 16 birds maintained in constant darkness during a fortnight, when they were 1 month old, and when they were 19 ± 3 months old. We used birds from selected lines in order to test individuals of rhythmic and arrhythmic phenotypes. Three parameters were studied: the period, the clarity of the rhythm and the level of activity. All the birds kept the same circadian phenotype during the both recordings. For the rhythmic birds, the circadian period of feeding activity weakly lengthened, but this increase was not statistically significant. For all the birds, the clarity of the circadian rhythm and the level of activity per cycle decreased significantly with ageing. We found a positive relation between the ratios of the correlation coefficients of circadian activity, expressing the clarity of the rhythm, when the birds were young and older. So, it seems that a basic decrease of clarity as well as of level of activity, though these two parameters are not directly linked, take place with ageing. The results are discussed in terms of causal and functional aspects of circadian rhythm of feeding activity.