Breeding seasons of sea-birds in the Galapagos Islands

The sea-birds breeding in the Galapagos Islands show a diversity of breeding cycles. Some species have rigidly fixed annual breeding while others breed throughout the year but have peaks of breeding at less than annual intervals. The eight species which have non-annual breeding are probably breeding as often as possible with the interval between the end of a breeding attempt and the start of the next being the time needed to moult the wing and tail feathers. Only one species is definitely known to breed and moult at the same time.
Although there are well marked seasonal fluctuations in the sea temperature, regular sampling failed to demonstrate any regular fluctuations in the surface plankton. The available evidence suggests that food for some sea-birds is erratic and unpredictable. Some non-annual breeding species have their breeding synchronized by severe food shortages which delay breeding, presumably because females cannot find enough food to form eggs, until conditions improve.
Timing of the breeding season in annual breeders is less easily explained but some species may be feeding well away from the islands in areas where there is a regular fluctuation in the food supply. Most of the annual breeders have prolonged breeding seasons and in two species breeding is out of phase on different islands. Perhaps species are influenced by some weak annual variation in food supply which makes it disadvantageous to breed in a few months of the year.     

Why renew fresh feathers? Advantages and conditions for the evolution of complete post‐juvenile moult

Juveniles of several passerine species renew all of their fresh juvenile feathers immediately after fledging (complete post‐juvenile moult), in contrast to the majority, which perform a partial post‐juvenile moult. To understand the adaptive roles of this phenomenon we compared the quality of juvenile plumage in species that perform a complete post‐juvenile moult with that of species which perform a partial post‐juvenile moult; we similarly compared juveniles and adults in each of these groups. The quality of feathers was measured by mass of primaries, colour, and length. In species which perform a complete post‐juvenile moult the plumage quality of second‐year individuals, in their first breeding season, is similar to the plumage quality of adults, unlike those species that perform a partial post‐juvenile moult. In species which perform complete post‐juvenile moult, the quality of the feathers grown in the nest is lower than the quality of adult post‐breeding feathers. In contrast, in species which perform partial post‐juvenile moult the quality of the feathers grown in the nest is similar to that of adult post‐breeding feathers. We found that a complete post‐juvenile moult strategy is much more common 1) in residents and short‐distance migrants than in long‐distance migrants, 2) in southern latitudes, 3) in species with medium body mass and 4) in omnivores and granivores. Our results indicate two adaptive roles of the complete post‐juvenile moult strategy: 1) achieving high quality plumage in the first year which may increase individual survival probability and fitness and 2) allocating fewer resources to nestling plumage and more to nestling development, which enables the nestlings to leave the nest earlier, thus reducing the probability of encountering nest predators. We suggest that the complete post‐juvenile moult, immediately after fledging, is an optimal strategy in favourable habitats and under low time constraints, as in some tropical ecosystems.     

Weak breeding seasonality of a songbird in a seasonally arid tropical environment arises from individual flexibility and strongly seasonal moult

In some tropical birds, breeding seasonality is weak at the population level, even where there are predictable seasonal peaks in environmental conditions. It therefore remains unclear whether individuals are adapted to breeding at specific times of the year or flexible to variable environmental conditions. We tested whether the relative year‐round breeding activity of the Common Bulbul Pycnonotus barbatus arises due to within‐individual variability in breeding dates. We collected data from 827 birds via mist‐netting over 2 years with corresponding local weather data. We used a combination of climate envelope and generalized linear mixed models to explore how the timing of breeding is influenced by time of year, individual variation, rainfall and temperature in a West African savannah where seasonal precipitation determines annual variation in environmental conditions. We also pooled 65 breeding records from 19 individuals recorded between 2006 and 2017 based on brood patch occurrence and behavioural observation to compare within‐individual and population variability in breeding dates. We show that the breeding dates of individuals may be as variable as for the population as a whole. However, we observed a seasonal peak in juvenile occurrence that varies significantly between years. Models suggest no relationship between nesting and moult, and within‐year variation in rainfall and temperature, and birds were unlikely to breed during moult but may do so afterwards. Moult was very seasonal, correlating strongly with day length. We suggest that because environmental conditions permit year‐round breeding, and because reproductive output is subject to high predation risk, there is probably a weak selection for individuals to match breeding with variable peak conditions in the environment. Instead, moult, which always occurs annually and successfully, is probably under strong selection to match variable peak conditions in the environment so that long‐term survival ensures future reproduction.     

THE MOULT OF THE BULLFINCH PYRRHULA PYRRHULA

The distribution of feather tracts and their sequence of moult in the Bullfinch is described. The adult post-nuptial moult, which is complete, lasted 10–12 weeks, and the post-juvenile moult, which is partial, 7–9 weeks. Adult moult began with the shedding of the first (innermost) primary and ended with the replacement of the last. Variations in the rate of moult in the flight feathers were mainly achieved, not by changes in the growth rates of individual feathers, but in the number of feathers growing concurrently. The primaries were shed more slowly, and the onset of body moult delayed, in birds which were still feeding late young. In 1962, the onset of moult in the adults was spread over 11 weeks from thc end of July to the beginning of October, and in the two following years over the six weeks, from the end of July to the beginning of September. The onset of moult was delayed by late breeding, which itself occurred in response to a comparative abundance of food in late summer, markedly in 1962. In all years, the first juveniles to moult started at the end of July, and the last, three weeks after the latest adults. Juveniles moulting late in the season retained more juvenile feathers than those moulting earlier. During moult, adult and juvenile Bullfinches produce feathers equivalent to 40% and 33% respectively of their dry weights. In both, for much of the moult, an average of nearly 40 mgm. of feather material—some 0.6% of their dry-weight–is laid down each day. The remiges of the adult comprise only a seventh of the weight of the entire plumage, and it is suggested that their protracted moult results not so much from their energy requirements, as from the need to maintain efficient flight. Variation in the rate of moult in the remiges was much less pronounced than in the body feathers. Bullfinches were less active during moult than at other times of the year. The weights of both adults and juveniles increased during moult. The food during the moult period is described. In all years, most Bullfinches finished moulting just before food became scarce, even though this occurred at different times in different years. In one year, adults moulting latest in the season probably survived less well than those moulting earlier; the same was apparently true of the juveniles in all years. The timing of moult in the Bullfinch, and the factors initiating it, are discussed in relation to the breeding season and foodsupply near Oxford.     

Optimal moult strategies in migratory birds

Avian migration, which involves billions of birds flying vast distances, is known to influence all aspects of avian life. Here we investigate how birds fit moult into an annual cycle determined by the need to migrate. Large variation exists in moulting patterns in relation to migration: for instance, moult can occur after breeding in the summer or after arrival in the wintering quarters. Here we use an optimal annual routine model to investigate why this variation exists. The modelled bird's decisions depend on the time of year, its energy reserves, breeding status, experience, flight feather quality and location. Our results suggest that the temporal and spatial variations in food are an important influence on a migratory bird's annual cycle. Summer moult occurs when food has a high peak on the breeding site in the summer, but it is less seasonal elsewhere. Winter moult occurs if there is a short period of high food availability in summer and a strong winter peak at different locations (i.e. the food is very seasonal but in opposite phase on these areas). This finding might explain why only long-distance migrants have a winter moult.     

THE RELATIONSHIP BETWEEN CLIMATE AND ANNUAL CYCLES IN THE COTINGIDAE

This survey is based primarily or the state of moult of over 4000 specimens of cotingas from all parts of the neotropical region. The seasonality of moult thus revealed is combined with existing knowledge of breeding seasons and seasonal environmental changes in an attempt to work out the broad pattern of annual cycles and their relation to climate. Within any local population the date of onset of moult may vary according to sex and age. In genera in which both sexes participate in nesting, males and females begin to moult at about the same time, or the males slightly in advance of the females. In genera with marked sexual dimorphism, in which only the female attends the nest, males may begin to moult well before females, at about the time that the latter begin egg-laying. The former group includes the genera Pachyramphus and Tityra, comprising species that are largely insectivorous, and the latter group includes the more specialized frugivorous genera. In all areas with well-marked seasonality, the ‘frugivorous group’ moults on average before the ‘Pachyramphus group’. It appears to be a general rule for first-year birds to moult earlier than older birds. A regional survey embracing all parts of the neotropical region shows that the peak of onset of moult occurs towards the end of the dry season (frugivorous group) or early in the wet season (Pachyramphus group). The changing moult seasons, strikingly in conformity with the geographical changes in the period of heaviest rainfall, are traced along a number of transects from Mexico in the north to Paraguay and Bolivia in the south. Such evidence as there is suggests that the main period of onset of moult in the frugivorous and Pachyramphus groups coincides with the period when their food is approaching or at its seasonal peak of abundance. It seems that both breeding and moult, which are almost entirely mutually exclusive, are as far as possible timed to coincide with this most favourable period; but whereas the moult takes a more or less fixed length of time the period when breeding is possible varies greatly in different species. Widely different patterns of annual cycle may result from the interaction of the two processes. Examples are given both from the cotingas and from species of other families with similar ecology. The proximate factors controlling the timing of the moult are briefly considered. It is suggested that increasing food availability is the main environmental controlling factor, and that an endogenous circannual cycle of moult must also be involved.     

Annual cycle of the Helmeted Honeyeater Lichenostomus melanops cassidix, a sedentary inhabitant of a predictable environment

The annual cycle of breeding, moult and weight variation in the Helmeted Honeyeater Lichenostomus melanops cassidix , a sedentary bird of temperate southeast Australia, is documented. Breeding and moult were sequential unimodal annual events, whose timing was highly consistent between years. However, overlap of breeding and moult was frequent, and some individuals even commenced primary moult before laying their final clutch. The timing of the post-juvenile moult was coincident with that of adults. Early-hatched young moulted within a few months of hatching, but late-hatched young deferred moult for a year. Helmeted Honeyeaters were heaviest in autumn and early winter, and lightest in spring and early summer, a cycle most consistent with the redirection of all available resources to reproduction. The long breeding season (seven-and-a-half months) of the Helmeted Honeyeater, extensive overlap of breeding and moult, and other life-history attributes including small clutch size, are more consistent with the described bio-rhythmic patterns for birds in the humid tropics than the temperate zone. However, the Helmeted Honeyeater has a fairly rapid primary moult rate, unusual amongst species that overlap moult and breeding. This combination of attributes reflects the stable, somewhat seasonal environment occupied and the resource monopoly established by this tightly territorial subspecies. We speculate that extension of the breeding season, by overlapping breeding and moult, is one of the few options available to vary life-history strategies amongst 'old-endemic' Australian birds of the temperate zone.     

Urban living alters moult dynamics in a passerine

Urbanization and habitat fragmentation can alter the timing of life history events, potentially leading to phenological mismatches, carryover effects, and fitness costs. Whereas urbanization and fragmentation are known to alter important aspects of breeding in many bird species, little is known about the effects of urbanization and habitat fragmentation on moult. To investigate the effects of urbanization and fragmentation on the annual moult, we compared the moult dynamics (onset, duration, and intensity) of urban, fragmented forest, and contiguous forest populations of the Carolina chickadee, a North American resident passerine that moults once per year immediately following the breeding season. Over three years, moult dynamics were similar in contiguous and fragmented forest populations, but wing moult started significantly earlier, and onset of moult varied less among years, in urban chickadees than in forest chickadees (fragmented and contiguous habitats pooled). Duration of wing moult did not differ between urban and forest populations, but urban birds moulted significantly fewer feathers simultaneously during peak moult, suggesting that individual feathers grew more rapidly. Our results show that urban living alters critical aspects of moult dynamics in a widespread songbird. Given the importance of moult dynamics for fitness during subsequent life history stages, and the large number of songbird species inhabiting urban areas, these results reveal previously unrecognized and potentially costly carryover effects of urban living on songbirds.     

Moult Strategies Affect Age Differences in Autumn Migration Timing in East Mediterranean Migratory Passerines

Adult passerines renew their flight feathers at least once every year. This complete moult occurs either in the breeding areas, just after breeding (summer moult), or, in some long-distance migratory species, at the non-breeding areas, after arrival to the southern wintering area at the end of autumn migration (winter moult). The aim of this study was to relate moult strategies with the DMD, the difference in median migration date, through Israel, between juveniles and adults. Our data on autumn migration timing in juveniles and adults was based on ringing data of 49,125 individuals belonging to 23 passerine species that breed in Europe and Western Asia and migrate through Israel. We found that DMD was associated with moult timing. In all species that perform a winter moult, adults preceded juveniles during autumn. Among migrants who perform a summer moult, we found evidence of both migration timing patterns: juveniles preceding adults or adults preceding juveniles. In addition, in summer moulters, we found a significant, positive correlation between mean breeding latitude and DMD. Although previous studies described that moult duration and extent can be affected by migration, we suggest that moult strategies affect both migration timing and migration strategy. These two moult strategies (summer or winter moult) also represent two unique migration strategies. Our findings highlight the evolutionary interplay between moult and migration strategies.     

Moult in Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma

We recorded the age of individual wing and tail feathers of Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma of known age and breeding status at Bird Island, South Georgia. Breeders and non-breeders of both species moult their rectrices annually. Non-breeders moult primaries biennially. In the first year of a cycle, the outer three and some inner primaries are moulted descendantly; in the next year the inner primaries are moulted ascendantly, starting from primary seven. There is a general progression to moulting equal numbers of primaries in each half of the cycle by the time breeding starts at about 10 years of age. Grey-headed Albatrosses usually moult fewer primaries than Black-browed Albatrosses, particularly as 3-year-olds, when they undertake substantial plumage change in body moult. Most secondaries in Black-browed Albatrosses have been replaced once by age 4 years. Breeding Black-browed Albatrosses continue the moult pattern established as immatures whether they fail or not, as do failed Grey-headed Albatrosses. Successful Grey-headed Albatrosses, which breed again 16 months later, moult their three innermost primaries after breeding in the remainder of the current year and, after a period when moult is interrupted, renew the remaining primaries the following year. Comparisons between species and between failed and successful birds within species indicate that moult rate is not closely linked to the length of the interval between breeding attempts. Interspecies differences are better explained by breeding latitude, with tropical albatrosses moulting twice as fast as sub-Antarctic species, possibly reflecting food availability outside the breeding season.     

Moult in captive partially migratory and sedentary Australian silvereyes ( Zosterops lateralis ) (Zosteropidae)

In this study, we describe and compare the duration and timing of post-breeding moult of primary and secondary wing feathers, tail feathers, wing coverts and body feathers in captive partially migratory and non-migratory Australian silvereyes (Zosterops lateralis). This study allowed us to follow individual birds through the course of their moult and record the progression of moult in two populations. Both groups of birds underwent a conventional (or basic) post-breeding moult. While all birds followed a similar pattern of feather replacement, differences were found in the timing and duration of moult between migratory and non-migratory birds. The migratory birds generally started their moult earlier in the year and completed it before the non-migratory birds. The migratory birds revealed an overall uniformity in the timing and duration of their moult, while the non-migratory birds showed a greater degree of variability between individuals.     

Early exposure to a bacterial endotoxin advances the onset of moult in the European starling

In animals, events occurring early in life can have profound effects on subsequent life‐history events. Early developmental stresses often produce negative long‐lasting impacts, although positive effects of mild stressors have also been documented. Most studies of birds have investigated the effects of events occurring at early developmental stages on the timing of migration or reproduction, but little is known on the long‐term effects of these early events on moulting and plumage quality. We exposed European starling Sturnus vulgaris nestlings to an immune challenge to assess the effects of a developmental stress on the timing of the first (post‐juvenile) and second (post‐breeding) complete annual moult, the length of the flight feathers, and the length and colouration of ornamental throat feathers. The nestlings were transferred to indoor aviaries before fledgling and kept in captivity until the end of post‐breeding moult. Individuals treated with Escherichia coli lypopolysaccharide (LPS) started both moult cycles earlier compared to control siblings. Moult duration was unaffected by the immune challenge, but an advanced moult onset resulted in a longer moult duration. Moreover, female (but not male) throat feather colouration of LPS‐injected individuals showed a reduced UV chroma. We argue that an early activation of the immune system caused by LPS may allow nestlings to better cope with post‐fledging stresses and lead to an earlier moult onset. The effect of early LPS exposure was remarkably persistent, as it was still visible more than one year after the treatment, and highlighted the importance of early developmental stresses in shaping subsequent major life‐history traits, including the timing of moult in birds.     

Experimental dissociation of individual quality, food and timing of breeding effects on double-brooding in a migratory songbird

Annual reproductive success in many species is influenced by the number of breeding attempts within a season. Although previous studies have shown isolated effects of female quality, food, and timing of breeding on the probability of female birds producing second broods, to our knowledge, none have tested the relative importance of multiple factors and their interactions using simultaneous manipulations within populations of free-living birds. In this study, we show that individual quality and timing of breeding interact to affect the probability of double-brooding in female mountain bluebirds (Sialia currucoides). High-quality females (those that naturally initiated clutches early in the season) were more likely to double-brood, regardless of whether their hatching date was advanced or delayed, whereas later breeding, lower quality females were much less likely to double-brood when their first attempt was delayed. This indicates that annual fecundity of poorer quality (or younger) female bluebirds may be more sensitive to seasonal variation in environmental conditions. In addition, birds that were provided with supplemental food throughout first breeding attempts were more likely to double-brood in one of the study years, suggesting that female bluebirds may be energetically limited in their capacity to initiate a second brood. Females that had their first brood delayed also had a shorter inter-brood interval and were moulting fewer feathers during second broods compared to controls, while females in better condition showed more advanced moult in second breeding attempts. Taken together, our results demonstrate the combined effects of age- or individual quality-mediated energetic trade-offs between current and future reproduction, and between investments in offspring and self-maintenance, on annual fecundity of female birds.     

Climate change leads to differential shifts in the timing of annual cycle stages in a migratory bird

Shifts in reproductive phenology due to climate change have been well documented in many species but how, within the same species, other annual cycle stages (e.g. moult, migration) shift relative to the timing of breeding has rarely been studied. When stages shift at different rates, the interval between stages may change resulting in overlaps, and as each stage is energetically demanding, these overlaps may have negative fitness consequences. We used long‐term data of a population of European pied flycatchers (Ficedula hypoleuca) to investigate phenological shifts in three annual cycle stages: spring migration (arrival dates), breeding (egg‐laying and hatching dates) and the onset of postbreeding moult. We found different advancements in the timing of breeding compared with moult (moult advances faster) and no advancement in arrival dates. To understand these differential shifts, we explored which temperatures best explain the year‐to‐year variation in the timing of these stages, and show that they respond differently to temperature increases in the Netherlands, causing the intervals between arrival and breeding and between breeding and moult to decrease. Next, we tested the fitness consequences of these shortened intervals. We found no effect on clutch size, but the probability of a fledged chick to recruit increased with a shorter arrival‐breeding interval (earlier breeding). Finally, mark–recapture analyses did not detect an effect of shortened intervals on adult survival. Our results suggest that the advancement of breeding allows more time for fledgling development, increasing their probability to recruit. This may incur costs to other parts of the annual cycle, but, despite the shorter intervals, there was no effect on adult survival. Our results show that to fully understand the consequences of climate change, it is necessary to look carefully at different annual cycle stages, especially for organisms with complex cycles, such as migratory birds.     

Sex‐dependent response of primary moult to simulated time constraints in the rock sparrow Petronia petronia

There is growing evidence that moult speed affects plumage quality. In many bird species, males and females differ in terms of breeding effort, survival expectation and the relationship between fitness and plumage quality. Consequently, differences in moult strategies between the sexes can be expected. The aim of this study was to assess whether, under simulated time constraints and with no parental investment in the previous breeding season, males and females differed in: a) timing and duration of primary moult, b) growth rates of individual primary feathers, and c) number of concurrently growing feathers. We investigated the effect of time constraints generated by a treatment consisting of two decreasing photoperiods (slow changing photoperiod, SCP=2 min day^?1 and fast changing photoperiod, FCP=8 min day^?1) on the primary post‐nuptial moult of captive rock sparrows Petronia petronia. Females started to moult on average 14 and 15 days later than males in both experimental groups. Primary moult duration was 10 (FCP) and 24 (SCP) days longer in males than in females, and, within sex, 34 (females) and 48 (males) days longer in SCP birds than in FCP ones. Females renewed a larger number of primaries simultaneously (5.7% in FCP and 12.8% in SCP) and had a higher total daily feather mass grown (9.9% in FCP and 22.4% in SCP), even though daily growth rates of individual primaries did not differ between sexes. As a result, males and females completed their primary moult at the same time within treatment. The observed differences in timing, duration and energy allocation for primary moult between the sexes probably have a genetic basis, as birds did not engage in reproduction during the preceding breeding season.     

Differences in the timing and extent of annual moult of black-browed albatrosses Thalassarche melanophris living in contrasting environments

Moult entails costs related to the acquisition of energy and nutrients necessary for feather synthesis, as well as the impact of reduced flight performance induced by gaps in the wing plumage. Variation in moult strategies within and between populations may convey valuable information on energetic trade-offs and other responses to differing environmental constraints. We studied the moult strategies of two populations of a pelagic seabird, the black-browed albatross Thalassarche melanophris, nesting in contrasting environments. According to conventional wisdom, it is exceptional for albatrosses (Diomedeidae) to moult while breeding. Here we show that black-browed albatrosses breeding on the Falklands regularly moult primaries, tail and body feathers during chick-rearing, and the majority of those at South Georgia show some body feather moult in late chick-rearing. The greater moult-breeding overlap at the Falklands allows the birds to annually renew more primary feathers than their counterparts at South Georgia. The results of the present paper, pooled with other evidence, suggest that black-browed albatrosses from South Georgia face a more challenging environment during reproduction. They also serve to warn against the uncritical acceptance of conventional ideas about moult patterns when using feathers to study the ecology of seabirds and other migrants for which there is scant information at particular stages of the annual cycle.     

Postnuptial moult in a Belgian population of Nuthatches Sitta europaca

Postnuptial moult was studied in three consecutive years in a small population of Nuthatches. Fourteen to 25 individuals were captured in active moult each year with an average of 2.1 captures per bird per season. The total duration of moult was estimated as 88 days. Secondary moult was completed a few days after the end of primary moult. Primary moult rate was maximal at the beginning of moult, because many feathers were then growing simultaneously. Individual differences in the timing of moult were small, with a maximal spread of 21 days, and there was little variation between years. No differences in moult were found between sexes or age classes. Birds with failed broods moulted before successful breeders and early breeding females before late breeders. Duration and timing of moult are compared with other resident passerine species. A hypothesis based on summer territorial behaviour is put forward to explain the high degree of synchronization within the population and the relation between breeding and moulting.     

SHORT NOTES

Laycock, H. T. 1982. Moulting and plumage changes in the Thickbilled Weaver. Ostrich 53:91-101.

Thickoilled Weavers were studied in captivity, in the wild and as museum specimens. Moulting follows the normal passerine pattern, but a difference from related species is that there is no post-fledging moult of the flight feathers. Methods were devised for identifying isolated feathers and for aging trapped birds, this being easier in the male. After the breeding season the male undergoes eclipse, which has apparently not been described before, and loses his white forehead patches. Adult males and females moult about the same time, but second-year males moult six or eight weeks earlier. The duration of post-nuptial moult is about four months and is timed to occur during the season when there is maximum food availability. The use of a “moult score” is avoided in this account and the timing of feather loss substituted as having more real meaning.     

Influences of status and recent breeding experience on the moult strategy of the yellow-nosed albatross Diomedea chlororhynchos

The primary moult of individually colour-ringed, adult yellow-nosed albatrosses at nests on Gough Island was examined in 1983 and related to the status of each bird and its breeding history in the previous year. Adults renew only about half of their primaries each winter and suspend moult while breeding. Birds that bred successfully renewed fewer primaries than did unsuccessful birds or nonbreeders. There were no differences in primary moult between the sexes or in relation to size. Yellow-nosed albatrosses show complex wave moult as an adaptation to slow renewal of flight feathers. The energy, nutrient or time requirements for feather renewal may conflict with breeding annually so that there is a trade-off between the extent of moult desirable to maintain flight efficiency and the benefits of breeding in successive seasons.     

Seasonal changes in moult,body mass and reproductive condition in siskins Carduelis spinus exposed to daylength regimes simulating different latitudes

Birds use change in daylength during the year to time events during their annual cycles. Individual Eurasian siskins Carduelis spinus can breed and winter in widely separated areas in different years. Birds at different latitudes will experience different changes in photoperiod. So how does latitude affect photoperiodic control? Our aim in this study was to find whether Siskins caught from the wild in Britain and exposed to different photoperiodic regimes, typical of widely separated latitudes, would differ in the subsequent timing and duration of their moults and associated processes. Siskins were caught in late February and early March, and initially kept outside on natural photoperiods. From the spring equinox (21 March), they were divided into three groups kept under photoperiodic regimes that simulated latitudes 40°, 55° and 70°N respectively. All three groups showed highly significant subsequent changes in body mass, fat scores and cloacal protuberance size. Moult of the primary feathers started during June – August (mean 9 July), and lasted 61–99 days (mean 75 days). Birds that started to moult late in the season had shorter moult durations. All individuals showed lower mass and fat levels during moult than before or after moult. Crucially, there were no significant differences in the timing of these events between the three photoperiodic groups. Apparently these birds did not use prevailing absolute photoperiod or the prevailing rate of change in photoperiod to time moult‐related seasonal events, but used instead some other feature of the annual photoperiod cycle or some form of interval timer linked to photoperiod.