Wing moult in relation to autumn migration in adult Common Whitethroats Sylvia communis communis

Most long-distance passerine migrants in Sweden moult on breeding grounds before leaving on autumn migration to winter quarters. However, birds laying second or replacement clutches, or just breeding late, have too little time for a normal moult on the breeding grounds. When time is limited the birds may respond by making various adjustments to the moult, for example by moulting more quickly or by suspending the moult. In this study, the relationship between the performance of post-nuptial remex moult in Common Whitethroats breeding on Gotland, southeast Sweden, and autumn migration departure was investigated. The majority (77%) of the birds had interrupted moult in either the primaries or secondaries. Interruption of moult was more common among birds with a later onset date, as was asymmetry in moult between wings. The interruption of moult led to a significant time gain and moult completion was, consequently, more synchronized than moult onset. The results from this study indicate, in accordance with other data, that an early start of autumn migration is important. An early start may be crucial to facilitate the crossing of the Sahara Desert once the dry season has begun.     

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.     

Notes on the moult of red-backed shrikes ( Lanius collurio ) in their non-breeding range

Moult data from 302 museum skins and 11 trapped birds from sub-Saharan Africa show the course of flight feather moult. Most birds seem to start flight-feather moult soon after arrival in their southern African non-breeding ranges. About 75% of the birds had started before mid-December, i.e., during the main arrival time of the species. The mode of moult scores 1 and 2 was reached on 7 December; the last birds with a score of zero occurred in the first days of January. The mode of moult scores 5 and 6 was reached on 27 February. Thus, the time elapsed between the days when 50% of the population had reached the first and last stages of recorded moult was about 82 days; nine days later 75% had reached this last stage before moult was completed. Thus, individual moult may be estimated to cover about 80–90 days. The main moulting period is between mid-November and mid-March, thus covering about four months. No temporal difference was detected between males and females. A tendency for an advancement of adults compared to young birds was not statistically significant. According to the progress of the moult, sexing of young birds in the field is possible for 50% of the birds towards the end of January and for most birds before mid-February.     

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.     

Greater energy stores enable flightless moulting geese to increase resting behaviour

Many species of waterfowl undergo a post‐breeding simultaneous flight feather moult (wing moult) which renders them flightless and vulnerable to predation for up to 4 weeks. Here we present an analysis of the correlations between individual time‐budgets and body mass states in 13 captive Barnacle Geese Branta leucopsis throughout an entire wing moult. The daily percentage of time spent resting was positively correlated with initial body mass at the start of wing moult. Behaviour of individual birds during wing moult is dependent on initial physiological state, which may in turn be dependent on foraging ability; the storage of energy before the start of wing moult will help birds to reduce exposure to the dangers of predation.     

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.     

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.     

Edward Grey Institute of Field Ornithology

Suspended moult of the remiges is a feature of many long-distance migrant species; the authors, after examination of a large sample of birds trapped in Iberia, consider that it has adaptive significance and may help us better to understand how different moult patterns have evolved. They describe the various moult suspension strategies which permit birds to migrate with an unimpaired flight facility, and give particular attention to two remarkable departures from the normal, namely Savi's Warbler and Spotted Flycatcher.     

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 OF BUDGERIGARS MELOPSZTTACUS UNDULATUS

In captive Budgerigars Melopsitticus undulatus moult of primaries started in the middle of the tract and moved progressively inwards and outwards, the inner feathers being replaced faster than the outer ones. Full replacement of primaries took six to eight months and a new cycle of moult usually started before completion of the old cycle. Moult of secondaries followed no clear pattern and occurred less frequently than moult of primaries. Moult of rectrices started with the middle pair and moved progressively outwards on both sides. Complete moult of rectrices took about six months and a new cycle often started before completion of the old. Moult of the head and body occurred intermittently throughout the year. Birds fledged in juvenal plumage, they passed into first basic plumage with a partial moult (head and body feathers) and into definitive basic plumage with a moult of all contour feathers.
In the field in inland mid-eastern Australia, there were some birds replacing feathers and some with complete plumage in most months of the year. Birds with complete plumage may have been between moults or within a moult and between replacement of feathers. The proportion of birds in moult did not increase in intensity after breeding, or cease during breeding or before movements. Some birds of both sexes with gonads in a reproductive condition were replacing feathers. Rirds that were replacing feathers had similar lipid deposits to birds that had a complete plumage.     

Juvenile wing shape, wing moult and weight in the family Sylviidae

A study of 56 species of Sylviidae occurring in the western Palaearctic showed a significantly less extensive post-juvenile moult in those species which incur longer migrations to winter quarters than in species that migrate short distances. Species with the more extensive post-juvenile moult also undertook their first full moult in summer compared with the less extensive post-juvenile moult in species with a full moult in the winter. In 11 species, young birds had shorter wings and lower body mass than adults. These differences produced significantly lower wing loadings in young birds compared with adults. Those species undertaking a full moult in the winter had significantly more pointed wings than species with their full moult in the summer. I suggest that this difference is the result of winter-moulting species evolving from the probably basic strategy of a full post-breeding (summer) moult. Some species, such as the Barred Warbler Sylvia nisoria , may be in the process of changing the full-moult season from summer to winter.     

Of squeezers and skippers: factors determining the age at moult of immature African Penguins Spheniscus demersus in Namibia

We used banding and resighting records of 391 African Penguins Spheniscus demersus banded as chicks and later resighted during immature moult to explain the roles of date of fledging and age at moult in determining the season of moult and its timing within the season. Breeding was continuous, but immature moult occurred mainly during spring and summer. Age at immature moult extended over 11 months, from 12 to 23 months after hatching. Birds that fledged during summer and early autumn generally moulted during the next moult season (squeezers), whereas birds that fledged in late autumn, winter and spring skipped the next moult season to moult only the following season (skippers). There was a significant relationship between age at moult and moult date, with young birds moulting later in the season than older birds. The age at moult of immature birds appears to be constrained by minimum age, moult seasonality and plumage wear. Birds that fledged over nearly 2 years moult during one season. Counts of moulting immature African Penguins have not been used to estimate year-class strength and post-fledging survival owing to the wide range of ages at immature moult. Our results provide the means of assigning recruits to specific age groups.     

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.     

Flexibility in the timing of post-nuptial moult among Red-billed Queleas Quelea quelea in Botswana in relation to the timing of breeding

The timing of primary moult of adult Red-billed Queleas Quelea quelea, captured as they were completing an unusually late breeding attempt at Francistown, northern Botswana, in June 2004, was compared with the timing of moult of birds breeding earlier in the season in north-west Botswana during two earlier years, 1971 and 1972. Differences between years in the dates when local colonies finished breeding (mid-March to late June) and between two localities in the same year (mid-March and late May) were matched by corresponding differences in the estimated dates of moult onset, ranging from mid-April to mid-June. Flexibility in the timing of moult among Red-billed Queleas in southern Africa evidently enables birds to take advantage of unusually late breeding opportunities by delaying moult onset and overlapping moult and breeding at the end of the nesting cycle. Such flexibility may also include moult interruption to permit late breeding, although its incidence in southern Africa is apparently low.     

The effects of daylength and testosterone on the initiation and progress of moult in Starlings Sturnus vulgaris

The effects of daylength and of testosterone implants, before and after the beginning of moult, on the timing and rate of primary moult have been quantified. Female Starlings Sturnus vulgaris were moved from natural daylength in February to 13 h or 18 h of light per day (13L: 11D or 18L: 6D). Some of the birds on 18L: 6D were left on 18L: 6D throughout the experiment and others were transferred to 13L: 11D after 6 weeks, before moult had begun, or after 12 weeks, after moult had begun. Birds kept on 18L: 6D began to moult before birds kept on 13L: 11D, but the subsequent rate of moult was the same in both groups. A decrease in daylength before moult started slightly advanced the onset of moult. A decrease after moult had begun increased the speed of moult. Castrated male Starlings on 18L: 6D were given testosterone implants for different periods before or after the beginning of moult. Testosterone treatment which ended before moult would normally have started had little effect. Treatment extending beyond the normal start of moult considerably delayed or even prevented the onset of moult. Moult was arrested in birds which received testosterone after moult had begun. On removal of testosterone implants, moult began again from the point where it had stopped, but in some birds, all of the feathers which had been regrown recently were dropped again and regrown. These results are discussed in relation to the different patterns of moult seen amongst different species.     

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.     

Uropygial gland size,feather holes and moult performance in the House Sparrow Passer domesticus

Feather holes represent damage to the plumage of birds and are correlated with delayed moult. Uropygial gland size is negatively correlated with feather holes. Consequently, it was predicted that birds with smaller uropygial glands would have more feather holes, and that this would affect moult performance. I examined this prediction in the House Sparrow Passer domesticus. Individuals with smaller uropygial glands had more feather holes, and those with more feather holes moulted later and faster. Therefore, uropygial gland size seemed to affect moult performance via its effect on feather holes. Uropygial gland size may have a positive effect on plumage quality, through a negative effect on feather holes, and therefore on moult timing and speed.     

Timing and duration of moult in three populations of Purple Sandpipers Calidris maritima with different moult/migration patterns

Timing and duration of primary moult in three populations of Purple Sandpipers Calidris maritima were described and discussed in relation to the birds’ need to complete moult before the onset of winter, when resources are required for survival. We predicted that moult would be completed earlier by birds wintering at higher latitudes. The south Norwegian breeding population, which moults and winters along the coast of east Britain (54–57°N) had a mean starting date of 21 July for primary moult (16 July for females and 24 July for males), a mean duration of 61 days, and completed on 20 September. Resident Icelandic (64–65°N) birds had a mean starting date of 22 July for primary moult (17 July for females and 25 July for males), a mean duration of 51 days, and completed on 11 September. Birds moulting in north Norway (70°N) arrived in north Norway in suspended primary moult or without having started moult, and completed it there. They had a mean completion date of 2 November for primary moult (31 October for females and 3 November for males). Starting date and duration could not be estimated because some suspended moult for an undetermined period, but it was thought that they started in late August. It is likely that most originated from Russia. The onset of moult appears to be set by the end of breeding and there is little overlap in these two events. The earlier start of moult by females in all three populations may be because they abandon the males when the chicks hatch, leaving the males to attend the chicks. Although the duration of primary moult followed the expected trend, being fastest in north Norway and slowest in Britain, the onset of moult was so late in north Norway that they had an unexpectedly late completion date, despite their rapid moult. The late completion of primary moult in north Norway suggests that wintering in the far north may not pose the energetic constraints on Purple Sandpipers that had previously been supposed.     

Balancing moult data by subsampling non-moulting birds prior to regression analysis

During the analysis of moult records from the SAFRING database it was found that for some datasets the records were not evenly distributed temporally and the proportion of moulting to non-moulting birds was not what would be expected from random sampling. In an attempt to balance these data, the records of non-moulting birds were subsampled with different sample sizes prior to moult regression analysis, and the resulting moult estimates were then compared. The results suggest that subsampling non-moulting birds such that they occur in the expected proportion to actively moulting birds, based on the duration of moult, provides the best estimates of moult.     

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.