Inter-locality variation in reproductive success of the citril finch Serinus citrinella

Habitat quality is generally thought to affect breeding success. We tested this effect comparing differences in clutch size and reproductive success between citril finch Serinus citrinella sub-populations closely located (<5 km) but differing in habitat quality, within the Port del Comte mountain, in the Catalonian Pre-Pyrenees. We found that birds in the low quality area (Bofia) showed significantly lower hatching, breeding and nesting success than finches in the high quality area (Vansa). These differences in reproductive success fit well with recently found differences in citril finch body mass, fat score, diet, survival rate and speed of moult between these two localities.     

Plasticity in moult speed and timing in an arctic‐nesting goose species

Environmental constraints are strong in migratory species that breed in the Arctic. In addition to breeding, Anatidae have to renew all their flight feathers during the short arctic summer. We examine how temporal constraints and climate affect the phenology of flight feather moult in the greater snow goose Chen caerulescens atlantica, a High Arctic nesting species. We used a database of 1412 moulting adult females measured over 15 yr on Bylot Island, Nunavut. Ninth (9th) primary length was used to determine the moult stage and speed of feather growth. We found a positive relationship between median annual hatching and moult initiation dates and the slope did not differ from 1. The interval between hatching and moult initiation was thus rather fixed and geese did not initiate moult earlier when reproductive phenology was delayed. Nonetheless, there was no relationship between median hatching date and the date at which birds regained flight capacity, suggesting that date of end of moult is independent of the reproductive phenology. There was a trend for an increase in the speed of flight feather growth in years with delayed hatching date. This is the most likely mechanism that could explain moult phenology adjustment in this species. Finally, we found a positive relationship between 9th primary length (corrected for inter‐annual variations) and body condition, suggesting a delay in moulting for individuals in poor condition. These results suggest that moult plasticity is primarily governed by variations in feather growth speed. This phenotypic plasticity could be necessary to complete flight feather renewal before the end of the arctic summer, independently of reproductive phenology and spring environmental conditions. Our novel results suggest possible phenological adjustments through moult speed, which was considered constant in geese until now.     

Carotenoid plumage hue and chroma signal different aspects of individual and habitat quality in tits

We hypothesized that Blue Tits Cyanistes caeruleus and Great Tits Parus major from low quality habitat (small woods) would have less yellow ventral plumage than those from high quality habitat (large woods) because they moult faster and/or their diet contains fewer carotenoids. They moult faster because they moult later in the season and are subject to more rapidly shortening daylengths. We tested this using a database of the plumage coloration (chroma, hue and lightness) of birds breeding in woods of different sizes, by manipulating the speed of moult in captive Blue Tits, and by counting the abundance and size of caterpillars (the major source of dietary carotenoids) in the diet of nestlings. In accordance with our hypothesis, juveniles of both species (which moult about three weeks later than adults) were about 8% less saturated in colour (lower chroma) than adults, but there was no significant difference in chroma between habitats. However, both species did differ significantly in hue between large and small woods. Blue Tits forced to moult faster in captivity, at a rate similar to that caused by a month's delay in the start of moult, had yellow flank feathers that were 32% less saturated in colour than those allowed to moult more slowly. Blue Tit nestlings in large woods consumed 47% more caterpillar flesh (per gram of faecal material voided) than those in small woods, and Great Tit pulli 81% more. When habitat effects were controlled for in ANOVAs, Blue Tits mated assortatively on the basis of flank hue and Great Tits on the basis of flank lightness. Flank colour therefore has the capacity to provide information about the potential quality of both habitats, and individual birds, to potential colonists and sexual partners.     

The timing, duration and pattern of moult and its relationship to breeding in a population of the European Greenfinch Carduelis chloris

Moult was studied in 1 year among Greenfinches trapped in a garden in east‐central England. Over the period June–December 2003, 333 captures of 179 individual adults provided information on breeding condition, moult, body weight, sex and age (yearling or older adult, equivalent to birds in their second or later calendar years, respectively). About 95% of all birds (sex and age groups combined) started primary feather moult from 2 July to 14 August, and finished from 10 October to 22 November. The mean date of moult onset in the population as a whole was 24 July. On average, males began 8 days before females, and yearlings began 6 days before older birds. The mean duration of moult was 100 days, whether the figure was calculated for the population as a whole or just for the 36 individual birds that were caught more than once during moult. However, moult rate was slightly slower, and moult duration slightly longer, in yearlings than in older adults of both sexes. No evidence was found for any systematic relationship between moult onset date and rate (duration). Breeding and moult overlapped by up to 5 weeks or more in individual birds, and some birds probably started to moult as early as the incubation stage of their last clutch of the season. The cloacal protuberance (taken as indicative of breeding condition) had regressed in all males by the time the fifth primary was shed, and the brood patch had regressed and re‐feathered in all females by the time the fourth primary was shed. The bulk of feather replacement in the secondary, tail and body tracts occurred in the second half of primary moult, and after cloacal protuberances and brood patches were completely regressed. In all birds examined near the end of primary moult the secondaries were still growing, and would have continued growth for up to another 19 days or more, extending the end of the moulting season into December. Body mass during moult was affected significantly by sex and age, as well as by time of day, amount of food in gullet, reproductive condition and date. No firm evidence emerged that body mass was affected by moult stage, after allowing for effects of date and other variables (although there was a non‐significant negative relationship between moult stage and body mass in males). In the population as a whole, the breeding season (from first egg‐laying to independence of last young) was spread over 21 weeks and moult over 24 weeks. With an overlap between the two events at the population level of up to 9 weeks, the two processes together took up to 36 weeks, some 69% of the year.     

SEASONALITY, DENSITY AND DIVERSITY OF BIRDS OF A PAPYRUS SWAMP IN WESTERN KENYA

The commoner birds of a western Kenya papyrus swamp are listed. This avifauna is probably as rich as in any papyrus habitat, dominated by warblers (Sylviinae) in which interspecific competition between species of similar size is reduced by preference for swamp-edge rather than interior habitats, preference for papyrus over standing water, or vertical habitat partitioning. Comparisons with other west Kenyan habitats show that it is a specialized avifauna with low species diversity indices and few species. Density figures for common species are higher than in forest undergrowth or thicket. There is little ecological diversity of habitat in uniform stands of papyrus which form ecological islands, and this high density may be interpreted as a density compensation on a speciespoor ‘island’ compared to a species-rich ‘mainland’. Rainfall is the most seasonally variable climatic factor in west Kenyan papyrus habitats. In this climatic area of Uganda and western Kenya there is a modal egg-laying period from March to June coinciding with the long rains, and a postnuptial primary moult period from June to November, which extends into the short rains of October and November. On average, a complete moult of the remiges takes six or seven months. In general the moult of immatures begins and ends about two months later than adult moult, but birds reared during the short rains had primary moult only half complete at the beginning of the following long rains. There is very little evidence of interrupted moult. The 1969 rainfall pattern was exceptional, with the heaviest rainfall in February, and there is evidence of a correspondingly early onset of postnuptial moult in that year. Females moulted significantly earlier than males in 1969 whereas males moulted marginally earlier in other years, suggesting that female moult schedules are more flexible.     

Behavioural and morphological correlates of variation in the extent of postjuvenile moult in the Siskin Carduelis spinus

Siskins Carduelis spinus show great variation in the acquisition of adult plumage, so that yearling birds can be classified as either "delayed" (i.e. still showing yearling plumage) or "advanced" (i.e. with an adult plumaged appearance). The extent of moult in males is related to the size of their black bib, which in turn is highly correlated with their social dominance rank. Autumn male body mass is higher in advanced than in delayed moult birds, but by winter the relationship is reversed, suggesting a trade-off between investment in moult and subsequent body condition. Results were similar in Spain and Britain. A possible cost of advancing moult is suggested by an analysis of aggressive interactions at bird feeding tables which showed that adult males discriminate between delayed and advanced birds, directing most aggression towards adult-looking yearling males. The results suggest that the variation in the extent of postjuvenile moult is not only related to energetic constraints but has other important behavioural and ecological implications.     

Carry-Over Effects of Nonbreeding Habitat on Start-to-Finish Spring Migration Performance of a Songbird

For migratory animals, conditions during the nonbreeding period may carry-over to influence spring migration performance. Animals in low-quality habitats are predicted to be in poorer condition, show later migration timing, and travel at slower speeds. This can result in subsequent negative effects on fitness. We tested the hypothesis that nonbreeding season body condition and habitat quality carry-over to affect spring migration performance of a long-distance migratory songbird, the Wood Thrush (Hylocichla mustelina). We tracked individual birds between multiple breeding sites in North America and nonbreeding sites in Central America. First, we compared body condition of nonbreeding birds migrating to the same general region of the breeding range with spring migration performance (timing, speed, and duration) obtained from light-level geolocators. Second, we assessed the Normalized Difference Vegetation Index (NDVI) as a proxy for nonbreeding habitat quality, and predicted that birds from wetter habitat or in wetter years (higher NDVI) would show improved migration performance relative to birds from drier sites. We found no evidence of individual-level carry-over effects of nonbreeding season body condition on spring migration performance. Lower NDVI of nonbreeding habitat resulted in delayed spring migration departure, but this effect disappeared by arrival at breeding sites. Birds occupying drier nonbreeding sites migrated faster and for fewer days, compensating for their relatively late departure. We also documented a broader pattern in NDVI and migration timing and distance, in that birds that occupied the wettest areas in the southern part of the nonbreeding range departed significantly later and migrated farther. Our results suggest that individual carry-over effects of nonbreeding habitat quality may be compensated for by a faster and shorter migration strategy. At a broad scale, consistently later spring timing and longer migration distances were associated with the wettest areas (the highest quality habitats) of the Wood Thrush non-breeding range. This supports the theory that high-quality habitats offset the costs of farther migration, resulting in a leap-frog migration pattern.     

Moult speed constrains the expression of a carotenoid-based sexual ornament

We investigated the effect of moult speed on the expression of a sexually selected, carotenoid-based feather ornament in the rock sparrow (Petronia petronia). We experimentally accelerated the moult speed of a group of birds by exposing them to a rapidly decreasing photoperiod and compared the area and the spectral characteristics of their ornaments with those of control birds. Birds with accelerated moulting rate showed a smaller yellow patch with lower yellow reflectance compared to their slow-moulting counterparts. Considering that the time available for moulting is usually constrained between the end of the breeding season and migration or wintering, carotenoid feather ornaments, whose expression is mediated by moult speed, may convey long term information about an individual's condition, potentially encompassing the previous breeding season. Furthermore, the observed trade-off between moult speed and ornament expression may represent a previously unrecognized selective advantage for early breeding birds.     

Body weight, gonad development and moult in the Tawny owl (Strix alum)

Gonad development, moult and seasonal changes in body weight and composition in the Tawny owl Strix aluco were studied by examining the carcasses of 369 owls (mostly road casualties) supplemented by 112 weights of live birds. In breeding females laying was preceded by the accumulation of fat and to a lesser extent protein which meant that they weighed more at this time (February/March) than at any other. Females declined in weight after laying but were still heavy during incubation. In contrast, males and non-breeding females did not increase in weight before the start of the breeding season. Juveniles reached or even exceeded adult weight well before independence due to the deposition of fat. Even after the exclusion of diseased or contaminated individuals, 9·4% of the birds examined were identified as starving; most of these were in the autumn and were probably newly-independent young wandering in search of territories. In both sexes gonad maturation was of brief duration coinciding with the period (mid-March to mid-April) in which eggs are normally laid. Ovarian growth was biphasic. In the three months prior to the breeding season ovarian condition in different birds was positively correlated with body weight and it appeared that the largest ovarian follicles of females in poor condition failed to attain the size from which rapid growth to final ovulation occurs. in males testis size in the breeding season was correlated with pectoral muscle weight (an index to protein condition) but not body weight. The majority of adults commenced wing moult in June. The average duration of primary moult was estimated to be 77 days. Healthy birds replaced the primaries of both wings at the same rate but most diseased birds moulted asymmetrically and/or out of season. First-year birds renewed their body feathers between September and November. In the Tawny owl territory establishment, breeding and moult are temporally separated.     

Experimental test of a trade‐off between moult and immune response in house sparrows Passer domesticus

A trade‐off between immune system and moulting is predicted in birds, given that both functions compete for resources. However, it is unclear whether such a trade‐off exists during post‐breeding moult. This study tests such a trade‐off in the house sparrow (Passer domesticus). Males injected with an antigen (lipopolysaccharide) significantly moulted slower than sham‐injected males. Moreover, males whose seventh primaries were plucked to simulate moult showed smaller immune response to phytohaemagglutinin than control males, in which seventh primaries were clipped. A trade‐off between moult speed and body mass was also found. The results show a clear trade‐off between moult and immune response in the house sparrow: immune response negatively affected moult and moult negatively affected immune response. These findings suggest that only individuals in good condition may have an efficient moult and simultaneously respond effectively in terms of immunity to pathogens, which could explain how plumage traits honestly indicate parasite resistance in birds.     

Half a World Apart? Overlap in Nonbreeding Distributions of Atlantic and Indian Ocean Thin-Billed Prions

Distant populations of animals may share their non-breeding grounds or migrate to distinct areas, and this may have important consequences for population differentiation and dynamics. Small burrow-nesting seabirds provide a suitable case study, as they are often restricted to safe breeding sites on islands, resulting in a patchy breeding distribution. For example, Thin-billed prions Pachyptila belcheri have two major breeding colonies more than 8,000 km apart, on the Falkland Islands in the south-western Atlantic and in the Kerguelen Archipelago in the Indian Ocean. We used geolocators and stable isotopes to compare at-sea movements and trophic levels of these two populations during their non-breeding season, and applied ecological niche models to compare environmental conditions in the habitat. Over three winters, birds breeding in the Atlantic showed a high consistency in their migration routes. Most individuals migrated more than 3000 km eastwards, while very few remained over the Patagonian Shelf. In contrast, all Indian Ocean birds migrated westwards, resulting in an overlapping nonbreeding area in the eastern Atlantic sector of the Southern Ocean. Geolocators and isotopic signature of feathers indicated that prions from the Falklands moulted at slightly higher latitudes than those from Kerguelen Islands. All birds fed on low trophic level prey, most probably crustaceans. The phenology differed notably between the two populations. Falkland birds returned to the Patagonian Shelf after 2-3 months, while Kerguelen birds remained in the nonbreeding area for seven months, before returning to nesting grounds highly synchronously and at high speed. Habitat models identified sea surface temperature and chlorophyll a concentration as important environmental parameters. In summary, we show that even though the two very distant populations migrate to roughly the same area to moult, they have distinct wintering strategies: They had significantly different realized niches and timing which may contribute to spatial niche partitioning.     

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.     

The moult of the Little Stint Calidris minuta in the Kenyan rift valley

Moult data were collected during 1967–80 from some 6900 Little Stints in the southern Kenyan rift valley.
Adults typically moulted from summer to winter body and head plumage during September and early October, soon after arrival. The complete pre-winter wing and tail moult began in most adults between mid-September and early October. Some birds finished by December, but others continued until February and March. Individual duration was usually between 100 and 150 days. Adults which completed this moult early often remoulted outer primaries between January and early April.
Young birds acquired first-winter body plumage during October and early November. Some 90% had a complete pre-winter wing and tail moult. This usually began between December and early February, and finished during March or early April, taking about 70–100 days. In about 10% of young birds, flight feather moult was restricted to the outer primaries and inner secondaries. Birds adopting this strategy typically began moult late, during January or February. Short periods of suspension were common during pre-winter wing moult, particularly in adults. The difference in moult speed between adult arid first-winter birds was attributable in the primary, secondary and tail tracts to differences in numbers of growing feathers.
Practically all birds completed a pre-summer moult involving the entire body and head plumage, most of the tertials, some or all of the tail feathers and many wing coverts. Most birds began this moult between early February and late March, and finished between mid-April and early May. It was typically later and more rapid in first-year birds than adults. In late birds, the onset of pre-summer moult was linked to the final stages of pre-winter moult.
The wing moult of the Little Stint in different wintering areas is discussed. First-winter moult strategy is compared with that in other small Calidris species.     

Moult speed affects structural feather ornaments in the blue tit

Growing evidence suggests that structural feather colours honestly reflect individual quality or body condition but, contrary to pigment‐based colours, it is not clear what mechanism links condition to reflectance in structural feather colours. We experimentally accelerated the moult speed of a group of blue tits (Cyanistes caeruleus) by exposing them to a rapidly decreasing photoperiod and compared the spectral characteristics of their structural feather colours with those of control birds. Blue tits were sexually dimorphic on the UV/blue crown and on the white cheek feathers. Moult speed, however, dramatically reduced brightness and the saturation only on the UV/blue crown feathers, whereas structural white on the cheek feathers was basically unaffected by moult speed. Given that the time available for moulting is usually confined to the period between the end of the breeding season and migration or wintering, UV/blue colours, but not structural white, may convey long‐term information about an individual’s performance during the previous breeding season. The trade‐off between fast moulting and structural colour expression may represent a previously unrecognized selective advantage for early‐breeding 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.     

The effects of delaying the start of moult on the duration of moult, primary feather growth rates and feather mass in Common Starlings Sturnus vulgaris

In many species of birds there is a close relationship between the end of breeding and the start of moult. Late-breeding birds therefore often start to moult late, but then moult more rapidly. This is an adaptive mechanism mediated by decreasing day lengths that allows late-breeding birds to complete moult in time. This study asked how these birds complete moult of the primary feathers more rapidly, and the consequences of this on the mass of primary feathers. Common Starlings Sturnus vulgaris were induced to moult rapidly in one of two ways. In the first experiment, one group was exposed to artificially decreasing photoperiods from the start of moult, whereas the control group remained on a constant long photoperiod. The second experiment was a more realistic simulation. Two groups were allowed to moult in an outdoor aviary. One group started to moult at the normal time. In the other, the start of moult was delayed by 3 weeks with an implant of testosterone. The duration of moult was significantly reduced in both the group experiencing artificially decreasing photoperiods and the group in which the start of moult was delayed. The faster moult rate was achieved by moulting more feathers concurrently. The rate of increase in length of each of the primary feathers, and their final length, did not differ between groups. The rate at which total new primary feather mass was accumulated was greater in more rapidly moulting birds, but this was insufficient to compensate for the greater numbers of feathers being grown concurrently. Consequently, the rate of increase in mass of individual feathers, and the final feather mass, were less in the rapidly moulting birds. A 3-week delay in the start of moult is not an unrealistic scenario. That this caused a measurable decrease in feather mass suggests that late-breeding birds are indeed likely to suffer a real decrease in the quality of plumage grown during the subsequent moult.     

Breeding ecology and nest site selection in allopatric mainland Citril Finches Carduelis[citrinella] citrinella and insular Corsican Finches Carduelis[citrinella] corsicanus

The breeding ecology and nest site selection of mainland Citril Finches and insular Corsican Finches have been studied throughout their limited range. For many years both endemic forms were considered to be two sub-species; however, based on evidence from more recent molecular studies they have been split into two species. This study provides data on the variations in breeding ecology and nest site selection in the different sub-populations of these little studied species. A secondary aim was to search out evidence of ecological differentiation between mainland Citril Finches and insular Corsican Finches. We found that the studied sub-populations of both species largely overlapped in breeding ecology. Our data confirms the close similarity of Citril Finches and Corsican Finches, both which are, similar to mountain birds, well adapted to the local habitat conditions of their different mountain systems. Several differences were identified within the studied sub-populations of the two (sub-) species with respect to nest site selection, probably caused by environmental conditions and local predators. One of the main differences between the two species is that Citril Finches breed mainly in half-open conifer forests (especially pine forests), while Corsican Finches breed in the more open scrubby mountains of the Mediterranean islands dominated mainly by the Tree Heath as an adaptation to the different landscapes on the islands. In contrast to Citril Finches, this preference of the Corsican Finches for Tree Heath as nesting plants – even if suitable pines are available – is typical of the species. These behavioural changes result in a niche expansion into open habitats at lower altitudes. We suggest that the observed niche expansion and behavioural variations are not suitable criteria for taxonomic status, a proposal in contrast to that of Sangster [Ibis 142:487–490 (2000)]. We further suggest that the few ecological differences found in this study between the two (sub-)species are the result of the so-called insular syndrome, which includes changes in life history traits such as morphology, demography and behaviour.     

White tail spots in breeding Barn Swallows Hirundo rustica signal body condition during winter moult

The determinants and function of pigmentation of feathers and other tissues have been the focus of a large number of studies, particularly with respect to socio‐sexual communication. However, many birds exhibit depigmented white spots or bars on their feathers whose function is poorly understood. Here we assess whether white feather spots reflect phenotypic condition at the time of moult by investigating the covariation between spot size or shape and condition‐dependent feather growth rate, as gauged by width of the growth bars on the tail feathers of Barn Swallows. We found that feathers with higher growth rates had larger, less rounded white spots. In addition, variance in spot perimeter for a given spot area was larger in males than in females. This study is the first to provide evidence that features of white markings on feathers directly reflect body condition at the time of moult and can therefore reliably signal phenotypic quality in the context of socio‐sexual communication. In addition, the study highlights the potential communication function of the shape and not just the size of colour signals.     

Sex differences in settlement behaviour and condition of chiffchaffs Phylloscopus collybita at a wintering site in Portugal. Are females doing better?

In passerine birds, males are generally larger and dominant over females. In line with the dominance theory, in all known differential migrant passerines, females migrate further than males. However, there are alternative explanations to the dominance hypothesis, including the specialisation hypothesis, predicting that females should do better than males in habitats and/or regions to which they are specially adapted, and where they predominate in numbers. Few studies have aimed at comparing the behaviour and condition of males and females wintering in locations largely dominated by female birds. We studied a partly nomadic species, the common chiffchaff Phylloscopus collybita, at a wintering site in Portugal. Most individuals caught at this site were transients. The only consistent and relatively powerful predictor of settlement behaviour was sex. Almost all the birds that settled in the study area were female, while there was an almost even sex ratio in the transient sample. Females had higher muscle and post-juvenile moult scores when first captured. In addition, there was a significant sex-based difference in mass trajectories, with females maintaining body mass and males losing body mass when settled at the study site. Results from this study suggest that the poor performance of males was either due to inferior male competitive ability in a region/habitat where females predominate and/or it resulted from the fact that males that reach these wintering grounds are of inferior individual quality.     

Large‐scale geographic variation in iridescent structural ornaments of a long‐distance migratory bird

Iridescent colours produced during moult likely play an important role in pair formation in birds. We sought to quantify geographic variation in such colouration in a duck species, Eurasian teal Anas crecca, in winter (when mating occurs) to evaluate whether this variation reflects birds’ breeding origins or differential individual migration strategies in both males and females. We combined information on feather production region and individual attributes (body size, sex and age) of Eurasian teal from 82 wintering sites in France. Feather production region (moult site or natal origin) was inferred using feather deuterium values (δD_f). We performed spectral measurements to evaluate speculum colour and brightness contrasts for 1052 teal collected over four years. Colouration differed strongly among wintering regions, with birds wintering in eastern France exhibiting higher colour contrast than those wintering in the west. Body size and colouration were positively related. There were no differences in cohort‐specific δD_f values between separate wintering regions in France, indicating that within a winter quarter teal originated from areas across the entire breeding range. Overall, patterns of spatial variation in feather colouration were related most closely to body size which was consistent with predictions of a differential migration hypothesis, with larger and more colour‐contrasting birds wintering closer to their breeding grounds. Because moult speed is also known to affect colour production, early breeders or individuals that skipped reproduction may have invested more or earlier in their feather quality to gain potential advantages in monopolizing future mates.