Prebreeding moult, plumage and evidence for a presupplemental moult in the Great Knot Calidris tenuirostris

We studied the prebreeding moult and resulting plumage in a long-distance migrant sandpiper (Scolopacidae), the Great Knot Calidris tenuirostris , on the non-breeding grounds (northwest Australia), on arrival at the staging grounds after the first migratory flight (eastern China) and on or near the Russian breeding grounds (Russian data from museum specimens). We show that breeding plumage scores and breast blackness were affected not only by the increase in moulted feathers but also in the wearing down of overlaying pale tips of fresh feathers. Birds migrating from Australia and arriving in China had completed or suspended moult, but more moult must occur in Asia as Russian specimens had moulted more of their mantle and scapular feathers. Russian birds had significantly more red feathering on their upperparts than had birds in Australia or those arriving in China. The increase in reddish feathers cannot by accounted for simply by continuation of the prealternate moult. Instead, a third, presupplemental moult must occur, in which red-marked feathers replace some scapular and especially mantle feathers that were acquired in a prealternate moult only 1–3 months earlier. Great Knot sexes show little size and plumage dimorphism, whereas two other sandpipers that have supplemental plumages (Ruff Philomachus pugnax and Bar-tailed Godwit Limosa lapponica ) are thought to be highly sexually selected. Bidirectional sexual selection may therefore be involved in the evolution of a supplemental plumage in Great Knots.     

Effects of latitude on the trade-off between reproduction and moult: a long-term study with pied flycatcher

Long-distance migratory passerine birds are generally time constrained by reproduction and moult, which need to be completed before migration. Breeding and post-nuptial moult may overlap especially under time-constrained conditions (northern latitudes). Here, we analysed the timing of adult moult in relation to latitude, timing of breeding and reproductive effort in pied flycatchers (Ficedula hypoleuca) breeding in four widely separated populations (40-68° N). In males but not females, the proportion of moulting birds while provisioning nestlings increased with increasing latitude. This may suggest that a moult-breeding overlap is a strategy employed by male pied flycatchers to adjust to the short breeding season at northern latitudes. However, the moult-breeding overlap was more pronounced among males in the southernmost study population (Spain). In this population, males may decide not to invest more in reproduction, and start moulting at earlier breeding stage than in northern populations,or, alternatively, birds in the Mediterranean region are time constrained by the hot and dry summer. The trade-off between breeding and post-nuptial moult may be more important in some populations than in others, depending on the latitude of the breeding site. Our results show that a moult-breeding overlap imposes a fitness cost on males in terms of fecundity and breeding success.     

A comparative study of migratory behaviour and body mass as determinants of moult duration in passerines

Birds moult to maintain plumage function through life, but the factors that determine moult duration are poorly understood. In temperate areas, variation in moult duration could be largely associated with between-species differences in migratory behaviour (migrants have less time for moulting after breeding), and body mass (because the aerodynamic cost of rapid moult increases allometrically with body size). Moreover, if the energetic cost of transport favours a smaller body size in migratory species, then the effects of migratory behaviour and body mass on moult duration could be confounded. We conducted a comparative study of the duration of adult complete moult in 48 European passerine species, in relation to body mass and migratory behaviour (sedentary, short-distance migrants and long-distance migrants). Lighter and more migratory species moulted faster than heavier and more sedentary species, but migration was not associated with body mass. If accelerated moult compromises the success of migration, changes in the physiology or phenology of moult in migratory birds are better interpreted as adaptive responses to compensate for such costs.     

Weak migratory connectivity,loop migration and multiple non-breeding site use in British breeding Whinchats Saxicola rubetra

Determining the links between breeding populations and the pressures, threats and conditions they experience presents a challenge for the conservation of migratory birds which can use multiple sites separated by hundreds to thousands of kilometres. Furthermore, migratory connectivity – the connections made by migrating individuals between networks of breeding and non-breeding sites – has important implications for population dynamics. The Whinchat Saxicola rubetra is declining across its range, and tracking data from a single African non-breeding site implies high migratory spread. We used geolocators to describe the migration routes and non-breeding areas of 20 Whinchats from three British breeding populations. As expected, migratory spread was high, with birds from the three populations overlapping across a wide area of West Africa. On average, in non-breeding areas, British breeding Whinchats were located 652 km apart from one another, with some likely to share non-breeding areas with individuals from breeding populations as far east as Russia. Four males made a direct non-breeding season movement to a second, more westerly, non-breeding location in January. Autumn migration was through Iberia and around the western edge of the Sahara Desert, whereas spring migration was more direct, indicating an anticlockwise loop migration. Weak migratory connectivity implies that Whinchat populations are somewhat buffered against local changes in non-breeding conditions. If non-breeding season processes have played a role in the species’ decline, then large-scale drivers are likely to be the cause, although processes operating on migration, or interactions between breeding and non-breeding processes, cannot be ruled out.     

Phylogenetic analyses of the diversity of moult strategies in Sylviidae in relation to migration

Moult in birds is highly variable both within and among bird genera. The aim of the present study was to make an extended phylogenetic analysis of the diversity of moult strategies within Sylviidae in light of the recent phylogenies based on molecular data, and with the methodology of matched-pairs analysis. In the present study we analysed 141 sylviid taxa and, to improve character reconstruction, 22 outgroup taxa. The study could corroborate the earlier results that post-breeding moult is the ancestral state in Sylviidae. Migratory habits were found to be ancestral within Sylviidae but resident habits have evolved several times with a few reverse transitions back to migratory habits. Transitions in main moult strategy were significantly related to both migratory vs. resident habits and to migratory distance, giving support to the hypothesis that moult in the non-breeding season is related to migration as such and long-distance migration, respectively. Both resident and migratory taxa used minor alternative moult strategies besides the main moult strategy and such within-taxon flexibility might be a basal trait in Sylviidae. We investigated three variables that included minor strategies and found no relationship between these and migratory habits. However, two of these variables (the potential to interrupt moult and the occurrence of moult in both the post- and non-breeding seasons) were significantly related to migration distance. We conclude that migration patterns has some influence on the choice of moult strategy, and that flexibility in timing of moult is widespread within Sylviidae and might be a basal trait. We argue that such flexibility might be a prerequisite for changes in migratory strategies.     

Seasonal colour change by moult or by the abrasion of feather tips: a comparative study

Many birds undergo seasonal changes in plumage coloration by prebreeding moult, abrasion of cryptic feather tips, or both. Seasonal dichromatism is thought to result from optimizing coloration to the conflicting demands of different life-cycle periods, sexual selection for conspicuousness being substantial during the mating season, whereas selection for camouflage and for social signals may act in all seasons. Furthermore, energetic and time demands may constrain the extent of moult, thereby limiting colour change. We investigated the relative importance of several factors in shaping this variation in a songbird clade using phylogenetic comparative methods. We found that prebreeding moult relates most strongly to breeding onset and winter diet, demonstrating that both time and food availability constrain feather replacement. Feather abrasion was best predicted by winter flocking behaviour, and secondarily by open habitats, implying that exposure to predators and the simultaneous need for social signalling may favour the expression of partially obscured ornaments in the non-breeding season. The combined occurrence of prebreeding moult and feather abrasion was associated with the polygynous mating system, suggesting that species under strong sexual selection may employ both strategies of colour change to ensure the full expression of breeding coloration.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 711–721.     

Non-migratory stonechats show seasonal changes in the hormonal regulation of non-seasonal territorial aggression

In many birds and mammals, male territorial aggression is modulated by elevated circulating concentrations of the steroid hormone testosterone (T) during the breeding season. However, many species are territorial also during the non-breeding season, when plasma T levels are basal. The endocrine control of non-breeding territorial aggression differs considerably between species, and previous studies on wintering birds suggest differences between migratory and resident species. We investigated the endocrine modulation of territorial aggression during the breeding and non-breeding season in a resident population of European stonechats (Saxicola torquata rubicola). We recorded the aggressive response to a simulated territorial intrusion in spring and winter. Then, we compared the territorial aggression between seasons and in an experiment in which we blocked the androgenic and estrogenic action of T. We found no difference in the aggressive response between the breeding and the non-breeding season. However, similarly to what is found in migratory stonechats, the hormonal treatment decreased aggressive behaviors in resident males in the breeding season, whereas no effects were recorded in the non-breeding season. When we compared the aggressive responses of untreated birds with those obtained from migratory populations in a previous study, we found that territorial aggression of resident males was lower than that of migratory males during the breeding season. Our results show that in a resident population of stonechats T and/or its metabolites control territorial aggression in the breeding but not in the non-breeding season. In addition, our study supports the hypothesis that migratory status does modulate the intensity of aggressive behavior.     

Different means to the same end: long-distance migrant seabirds from two colonies differ in behaviour, despite common wintering grounds

Although seabirds that are trans-equatorial migrants show apparently broad overlap among populations in the non-breeding season, such large-scale pattern may conceal subtle but nevertheless key differences in migratory behaviour. These specializations could reflect adaptation to different environments during the breeding season, carry-over effects from the breeding to the nonbreeding period, or asymmetries in competitive ability of birds of different origin. We compared the migratory and wintering behaviour of Cory's shearwaters Calonectris diomedea nesting in Berlengas and in the Selvagens, two colonies in contrasting oceanographic environments, separated by ca. 1200 km. Although no differences were found in winter distribution, there was a marked divergence in timing, route and the use of staging areas during the postbreeding (autumn) migration. Birds from Berlengas typically travelled to oceanic waters in the North Atlantic for an extended stopover, whereas those from Selvagens rarely did so. In the South Atlantic, birds from Selvagens spent more time in flight, perhaps because they had higher energy and nutrient requirements for feather replacement compared to birds from Berlengas, which moult more flight feathers during breeding. Stable isotope analyses of feathers suggested that this variation in activity patterns was unrelated to trophic ecology. Differences in migration routes and stopovers may expose populations to distinct threats, and should be taken into consideration when defining units for conservation purposes and developing appropriate management strategies.     

Life history varies with migratory distance in western sandpipers Calidris mauri

The propensity of migratory waders to remain on the non-breeding grounds during the arctic breeding season ("oversummer") in their first biological year of life ("juveniles") may be latitude, and thus migratory distance dependent. We compared the extent of preparation for northward migration of western sandpipers Calidris mauri spending the non-breeding season in México and Panamá during 1995–1998. During winter residency and premigratory periods, we measured body mass and scored the extent of dull basic versus bright alternate breeding plumage of captured juveniles and adults (second biological year or older), and obtained additional plumage scores from observations of uniquely colour banded birds. Nearly all western sandpipers in México prepared for northward migration by increasing body mass and moulting into breeding plumage. In Panamá, most adults prepared for migration, but few, if any, juveniles did so. Patterns of body mass and breeding plumage development do not generally support the hypothesis that oversummering by juveniles results directly from less efficient foraging or from resource competition with adults. We suggest instead that costs directly associated with migratory distance per se influence the life history strategies of sandpipers spending the non-breeding seasons at different latitudes. This latitudinal difference should interact with the well documented sex-ratio cline in non-breeding distribution (male western sandpipers predominating in northern parts of the range and females in southern parts). This suggests that females have more conservative life histories, prioritizing first year survivorship, relative to males that instead weight first-year breeding opportunities.     

Carry‐over effects and compensation: late arrival on non‐breeding grounds affects wing moult but not plumage or schedules of departing bar‐tailed godwits Limosa lapponica baueri

In the annual cycle of migratory birds, temporal and energetic constraints can lead to carry‐over effects, in which performance in one life history stage affects later stages. Bar‐tailed godwits Limosa lapponica baueri, which achieve remarkably high pre‐migratory fuel loads, undertake the longest non‐stop migratory flights yet recorded, and breed during brief high‐latitude summers, may be particularly vulnerable to persistent effects of disruptions to their rigidly‐timed annual routines. Using three years of non‐breeding data in New Zealand, we asked how arrival timing after a non‐stop flight from Alaska (>11 000 km) affected an individual godwit's performance in subsequent flight feather moult, contour feather moults, and migratory departure. Late arrival led to later wing moult, but godwits partially compensated for delayed moult initiation by increasing moult rate and decreasing the total duration of moult. Delays in arrival and wing moult up to 34–37 d had no apparent effect on an individual's migratory departure or extent of breeding plumage at departure, both of which were extraordinarily consistent between years. Thus, ‘errors’ in timing early in the non‐breeding season were essentially corrected in New Zealand prior to spring migration. Variation in migration timing also had no apparent effect on an individual's likelihood of returning the following season. The bar‐tailed godwits’ rigid maintenance of plumage and spring migration schedules, coupled with high annual survival, imply a surprising degree of flexibility to address unforeseen circumstances in the annual cycle.     

Primary moult, body mass and migration of Grey Plovers Pluvialis squatarola in Britain

Long-distance migrants have evolved complex strategies for the timing of their annual moult, fattening and migration cycles. These strategies are likely to vary at different stages of a bird's life. Ringing data on 6079 Grey Plovers Pluvialis squatarola , caught on the Wash, England, between 1959 and 1996, were analysed to relate migratory strategies to patterns of primary moult and body mass changes. Adults returning from breeding grounds had a shorter and delayed primary moult (duration 90 days, starting date 19 August) in comparison with over-summering birds (duration 109 days, starting date 5 June). Three categories of migrant adults were identified on the basis of primary moult and body mass: (1) birds which did not moult, but increased body mass and migrated further south; (2) birds which moulted 1–3 inner primaries, suspended moult, increased body mass and migrated; and (3) birds which completed or suspended moult and wintered locally. In birds of the second category, timing of primary moult and body mass increase overlapped. Among wintering birds, 38% were in suspended moult. Ninety-six per cent of birds that suspended moult at the beginning of winter were males and almost all completed moult in spring. Grey Plovers which left Britain in autumn had an average body mass of 280 g, enough to reach southern Morocco without refuelling. Both wintering adults and first-year birds showed a prewinter body mass increase, peaking in December. Adults had a synchronized premigratory body mass increase in May, which suggested a negligible presence of African migrants. The average departure mass for spring migration, estimated at 316 g, would allow birds to fly non-stop to the Siberian breeding grounds in western Taymyr.     

Endogenous control of migration and calendar effects in an intratropical migrant, the yellow-green vireo

Endogenous circannual rhythms control the time course for moult, migratory fattening and autumn migration in juveniles of several bird species that breed in the temperate zone. Exogenous factors, such as daylength, can also exert a measure of control: photoperiodic cues detected by birds that hatch late in the season induce accelerated juvenile development, assuring that late-hatched young migrate at the same time as early-hatched young. Whether these same mechanisms of control also apply to birds that migrate between breeding and nonbreeding areas entirely within the tropics at latitudes characterized by little seasonal variation in photoperiod is unknown. We conducted a common-garden experiment in Panama (9°N) in which we hand-reared wild-caught nestling yellow-green vireos, Vireo flavoviridis, under a constant photoperiod and monitored them for the expression of juvenile moult, migratory fattening and migratory activity. Even in the absence of a seasonal photoperiodic cue, juveniles moulted, accumulated fat reserves and initiated migratory activity, suggesting endogenous control of these processes. Age at the onset of moult, migratory fattening and migratory activity were each significantly negatively correlated with hatch date, however, so that the expression of these three processes was synchronized among juveniles with respect to the time of the season. We suggest that the slight differences in daylength perceived either by the nestlings themselves in the short time before they were collected (at 6-8 days of age) or by the adult females during egg production influenced rate of nestling development, thus allowing later-hatched young to moult, accumulate fat and migrate at a younger age than early-hatched young. Remarkably, photoperiod differed between the earliest and latest hatch dates in this study by only 33 min.     

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.     

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.     

Fat reserves of migrating passerines at arrival on the breeding grounds in Swedish Lapland

Mist-net capture data taken during 6 years (1988–1990 and 1992–1994) of field work were used to describe the arrival sequences and fat loads of nine species of migratory passerines which breed in a near-Arctic environment in Swedish Lapland. Long-distance migrants arrived with significantly larger mean fat reserves than did medium- and short-distance migrants. Long-distance migrants carried fat loads at arrival which corresponded to potential remaining flight distances between 242 and 500 km. When females and males arrived on the breeding grounds simultaneously, females carried significantly larger energy reserves than did males in seven out of nine species. In contrast, when the sexes showed a significant difference in median arrival date (two out of nine species), there was no difference in mean fat load carried into the breeding area. A relationship was found between the migratory habits and foraging ecology of each species and the amount of fat reserves at arrival, suggesting that species-specific migratory distances and feeding habits determine the amount of fat that is needed during the transition period between migration and onset of breeding. The short growing season in the study area restricts the time available for breeding and moult, and large energy reserves at arrival may speed up the breeding schedule to counteract possible time constraints. Overloading at the last stopover site during spring migration may be an adaptation allowing birds to cope with a restricted time frame for breeding and moult at high latitudes.     

Range-wide migration corridors and non-breeding areas of a northward expanding Afro-Palaearctic migrant,the European Bee-eater Merops apiaster

Across their ranges, different populations of migratory species often use separate routes to migrate between breeding and non-breeding grounds. Recent changes in climate and land-use have led to breeding range expansions in many species but it is unclear whether these populations also establish new migratory routes, non-breeding sites and migration phenology. Thus, we compared the migration patterns of European Bee-eaters Merops apiaster from two established western (n = 5) and eastern (n = 6) breeding populations in Europe, with those from a newly founded northern population (n = 19). We aimed to relate the breeding populations to the two known non-breeding clusters in Africa, and to test for similarities of migration routes and timing between the old and new populations. Western Bee-eaters used the western flyway to destinations in West Africa; the eastern birds uniformly headed south to southern African non-breeding sites, confirming a complete separation in time and space between these long-established populations. The recently founded northern population, however, also used a western corridor, but crossed the Mediterranean further east than the western population and overwintered mainly in a new non-breeding area in southern Congo/northern Angola. The migration routes and the new non-breeding range overlapped only slightly with the western, but not with the eastern, population. In contrast, migration phenology appeared to differ between the western and both the northern and the eastern populations, with tracked birds from the western population migrating 2–4 weeks earlier. The northern population thus shares some spatial traits with western Bee-eaters, but similar phenology only with eastern population. This divergence highlights the adjustments in the timing of migration to local environmental conditions in newly founded populations, and a parallel establishment of new breeding and non-breeding sites.     

THE MIGRATION SYSTEM OF THE CURLEW SANDPIPER CALIDRIS FERRUGINEA IN AFRICA

Elliot, C: C. H., Waltner, M., Underhill. L. G., Pringle, J. S. & Dick, W. J. A. 1976. The migration system of the Curlew Sandpiper Calidris ferruginea in Africa. Ostrich 47:191-213. Data on ringing and recoveries of Curlew Sandpiper, mainly from the Cape, South Africa are presented. Possible migration routes to the breeding grounds are considered in the light of these and other recoveries from the rest of Africa. Retraps show that the species exhibits ortstreue and some evidence is presented which suggests that some birds may travel together and stay in the south in the same flock during one and subsequent migrations. Sex ratio statistics show an excess of females. Adults complete a full primary moult in the Cape between September and February, taking about 140 days but there is a lot of individual variation. Data from Mauritania show primary moult starting faster, a month earlier than in the Cape, and arrested moult in a few adults. The difference may be because Mauritanian birds move on further south while the Cape is the end point of the migration. Kenyan moult records from the Rift Valley follow the Cape pattern except that some birds arrest moult and finish later. Juvenile moult is shown to be different from that of adults, involving only a moult of the outer primaries and taking place during the overwintering period, April to August. All juveniles in the Cape are thought to overwinter and the modified moult to be an adaptation to this behaviour. The weight of adults but not juveniles increases markedly in the six weeks before migration. Fat and protein analyses suggest that the increase is entirely due to deposition of migratory fat. Kenyan birds have lower mean weights and deposit fat about two weeks later than those at the Cape. The nearer the non-breeding quarters are to the breeding grounds, the earlier moult starts and the later fat deposition takes place.     

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.     

Transition between moult and migration in a long-distance migratory passerine: organ flexibility in the African wintering area

Phenotypic flexibility of organs in migratory birds has been documented for a variety of species of different genera during the migratory period. However, very little is known about phenotypic mass changes of organs with respect to other events within the annual cycle. This seems particularly interesting when birds face different physiological challenges in quick succession. We investigated mass changes of 13 organs from garden warblers (Sylvia borin) during the transition from moult to migration. These long-distance migratory birds perform a complete moult within their wintering area just shortly before the onset of spring migration. Birds were sampled in three successive stages according to their moult status: group I consisted of birds with growing primary or secondary wing feathers, group II consisted of birds with completed wing moult but with still moulting body feathers, and group III consisted of birds that had completed wing moult and body moult. Size-corrected flight muscle, kidney mass, and pancreas mass differed significantly among the three groups. Flight muscle was heaviest in birds that were about to leave their wintering area (group III) compared with birds still in body moult (group II). Kidney and pancreas showed a pattern similar to each other, with the heaviest mass occurring in birds with moulting wing feathers (group I) and significantly reduced mass in birds that had completed wing moult (group II) or both wing and body moult (group III). Mass reductions of kidney and pancreas during the transition from moult to migration are considered to be related to the demands of moult, while increased flight muscle may be due to moult, migration, or both. Phenotypic mass changes of organs in birds occur during their migration, but they also occur during the transition between other phases of the annual cycle such as moult and migration and are not restricted to the flight muscle.     

Lesser Whitethroats under time-constraint moult more rapidly and grow shorter wing feathers

Migrating passerines moulting in the breeding quarters before autumn migration sometimes end up with less time than needed for a normal moult. To deal with this the birds could for example suspend moult or moult faster. In this paper we investigate the effect of an induced time-constraint on the moult of Lesser Whitethroats Sylvia curruca . The time-constraint was induced through a shift in light regime large enough to transfer the birds to a date when, under normal conditions, they already should have started moulting. Time-constrained birds moulted faster and also grew shorter wing feathers, resulting in a shorter wing, compared to control birds. Only one individual responded by interrupting moult and retained a number of inner primaries unmoulted. The observed adjustments of moult, and the higher fuel loads towards the end of moult, are consistent with the ideas that time is an important factor in bird migration, affecting not only migration but also the events preceding it.