Primary moult in the annual cycle of adult African Oystercatchers Haematopus moquini

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.

Across all bird species, latitude plays an important role in determining patterns in timing, duration, and synchronisation of primary moult but, apart from Africa, moult studies at the southernmost limits of the continents and islands in the southern hemisphere are lacking. The focus of this study is the self-introduced silvereye (tauhou, Zosterops lateralis) in New Zealand, one of the most southern countries in the world. Moult data collected by bird banders during the period 1978–2022 were analysed using the Underhill-Zucchini moult model. Silvereyes had an estimated primary moult duration of 74 days, with a mean population start date of 3 February and a mean completion date of 19 April. Post-breeding primary moult in adult silvereyes starts soon after the breeding season and ends shortly before some of the more southern birds embark on their seasonal northward migratory movements. Juvenile primary moult is estimated to start approximately two weeks after the start of post-breeding moult in adults. A literature review suggested that primary moult duration for Zosterops species is similar regardless of latitude, but the timing of moult is variable and adjusted to local conditions.

The onset and duration of primary moult were investigated for adult Red-billed Queleas (Quelea quelea) in southern Africa. The duration of moult was shortest in Namibia (75 days), intermediate in Botswana (83 days) and longest in Gauteng Province (101 days) and the Eastern Cape (124 days), South Africa. The timing of the onset of moult was similar in Namibia and Botswana (21 and 31 May respectively), but considerably earlier in the Eastern Cape and Gauteng Province (6 and 23 April respectively). Completion of primary moult was well synchronised, ending in August in all sub-regions. Production of feather mass was uniform and speed of moult was controlled by the rate of growth of individual primaries. When moult was faster, fewer feathers grew simultaneously, possibly to reduce the aerodynamic effect of the wing-gap. Red-billed Queleas are thought to migrate relative to the movement of rain fronts, allowing possible multiple breeding events in one season. In southern Africa, Queleas are present throughout their range all year, and a proportion of the population moves short distances in apparently random directions. The large differences in timing and duration of moult in this study only support the short-distance ‘rainfall-migration’ model.

The primary moult of the Brambling Fringilla montifringilla was studied between 1988 and 1991 at Ånnsjön (63°15'N; 12°28'E) in the Swedish mountain region. The duration of primary moult was estimated in four different ways: 1) By linear regression of population data; 2) By calculating the mean duration of moult of 34 recaptured birds, assuming a linear relationship between time and moult progression; 3) By using data from the same recaptured birds but correcting for the non-linear progression of moult; 4) By using field data on the rate of shedding of different primaries and the growth rate of individual feathers to construct a moult score versus time curve. Linear regression of population data gave results varying from 32 to 70 days depending on population and method of analysis. The other three methods all resulted in a primary moult duration of 58–60 days. The recaptured birds often showed a weight decrease between captures but this seemed not to affect the moult speed. The mean starting date of moult of the population varied from 8 July to 18 July in the four years. The males tended to start a little earlier than the females, but the difference is not significant. The estimated duration of primary moult (ca 59 days) is considerably longer than the result (46.5 days) of another recently published study. The difference is probably due to different methods of analysis.

We describe the migration, biometrics and moult of Red Knot Calidris canutus canutus in southern Africa and compare them with the biometrics and moult of Calidris canutus islandica in northern Europe to examine possible adaptations to different environments during the non‐breeding season. Northward and southward migration of C. c. canutus took place along the coast of Western Europe and there was one recovery in West Africa (Mauritania), suggesting a coastal migration round West Africa rather than migration across the Sahara, as recorded in other waders. Adult Knots in South Africa had no additional fattening in November–January (fat index of 7%), in contrast to C. c. islandica wintering in Britain. This is consistent with the theory that extra fat is required only where food shortages are likely. The bills of canutus were longer than those of islandica but their wings were shorter, confirming the sub‐specific assignments and origin of this population. The average duration of primary moult in South Africa was 95 days, shorter than that of other Arctic‐breeding waders that moult in South Africa, but longer than of islandica moulting in Scotland (77 days). Mean starting and completion dates were 20 July and 5 October for islandica and 25 October and 28 January for canutus. The timing and duration of primary moult for these two subspecies suggest that waders need to complete moult before the northern winter when food supplies are limited, whilst waders in benign climates face no such pressures. First‐year canutus either retained old primaries for much of their first year or had a partial moult of inner or other primaries. Adults departed on northward migration in mid‐April, having attained a mean departure mass of c. 190 g (maximum 232 g). The mean fat index at this time was 24% (maximum 29%) and the fat‐free flight muscle mass increased. The predicted flight range of 4000 km falls short of the distance to the first likely refuelling site in West Africa, suggesting that birds rely on assistance from favourable winds.

We compared the primary molt of the 4 species of skuas and jaegers (Stercorariidae) that breed in the Northern Hemisphere: Long-tailed Jaeger (Stercorarius longicaudus), Parasitic Jaeger (S. parasiticus), Pomarine Jaeger (S. pomarinus), and Great Skua (S. skua). We analyzed primary molt data of 1,573 individuals of multiple age classes, mostly collected from photographs taken at sea but also from museum specimens and beached individuals. Whereas molt duration generally increased with species' size, molt duration in Parasitic and Pomarine jaegers was surprisingly similar given their size difference. Larger species started primary molt earlier and showed more overlap with postbreeding migration, such that there was complete overlap in Great Skua but no overlap in Long-tailed Jaeger. Within jaeger species, the first primary molt cycle took longer than later molt cycles. We suggest that, unlike birds in their first primary molt cycle, birds in their second or subsequent primary molt cycles are time-c...

The grassland biome in South Africa has a summer rainfall and Southern Red Bishops Euplectes orix, Fan-tailed Widows E. axillaris, White-winged Widow E. albonotatus, Red-collared Widow E. ardens and Long-tailed Widow E. progne breed from October or November to March. Primary moult starts in late March or early April. The widows with long tails (Long-tailed and Red-collared Widows) have moult durations of two months, while the widows with shorter tails (White-winged and Fan-tailed Widows) had moult durations of 1.5–1.7 months. Moult ends in late May or early June. Long-tailed Widows have rounder wings than other weaver species, possibly because their larger size affects flight aerodynamics. In the winter rainfall region, Southern Red Bishops and Yellow Bishops E. capensis start breeding after the winter rains, from August–November, and moult starts in early December. Primary moult duration in Yellow Bishops is relatively long, at 3.4 months. Yellow Bishops grow individual primary feathers at an average rate of 21.3 days per feather, while the other species moult primaries more quickly: White-winged Widow 8.1 days, Fan-tailed Widow 11.3 days, and Red-collared Widow 14.4 days. The number of primaries growing simultaneously is similar in the different species. The longer duration of primary moult of the Yellow Bishop may be related to food.

Flight feather moult is an energetically expensive stage of the annual cycle of birds. Its timing is adjusted to other important time- and energy-demanding activities, including migration. In the vast majority of migratory birds, primary moult occurs before or after migration or moulting is suspended during migration. The Black-headed Gull is an exception: it starts moulting flight feathers at the onset of the autumn migration. The course of primary moult in this species is still poorly understood due to the difficulty in obtaining sufficient data from the entire period of flight feather replacement. In this paper, we employed digital photos taken in the field to estimate the start, variation in the start date and duration of primary moult in adult and immature Black-headed Gulls, by using the Underhill–Zucchini likelihood moult model. On average, immatures started their moult on 7 June, 25 days earlier than adults, but their moult lasted 5 days longer. Consequently, there was a 20-day difference in the end of moult – that is, on average it occurred on 16 September and 6 October in immature and adult gulls, respectively. Adults showed greater variability in the mean primary moult start date than immatures, as the beginning of flight feather replacement may depend on breeding success (earlier after breeding failure) and on breeding phenology. The overlap of primary moult and migration produces a trade-off in resource allocation between those two processes, which leads to a low number of simultaneously growing primaries and a decrease in the growth rate of the two external, heaviest flight feathers. Existing reports of a later completion of primary moult in the first half of November in this species are based on the faulty assumption that the outermost primary is always the longest, which is not the case in 34% of individuals.

Feather moult is an important and energy‐demanding avian life‐history trait that is necessary to maintain the function of the plumage by replacing abraded feathers with new ones. However, during moult, aerodynamic capacity is temporarily impaired by the reduction and shape change of the flight surface. Therefore, among aerial birds, adaptations may evolve to reduce this impairment. Here, we studied the timing, duration and sequence of the annual complete moult of adult Little Swifts Apus affinis in northern Israel by examining the plumage of 55 individuals monthly in their colony. Primary moult occurs over 191.7 ± 24.0 days, representing 52.5 ± 6.6% of the annual cycle, and overlaps with the breeding season, a rare occurrence among small Palaearctic bird species. In addition, primary moult duration was significantly affected by its timing such that individuals that started to moult later had a shorter moult duration than those that started to moult earlier. This relationship is most likely to be a result of the time available for moult, which is limited by breeding and also by the cold season and the expected decline in food availability. Moult overlap with breeding or cold seasons may involve energetic and functional costs. Our results indicate two strategies that appear sequentially: (1) a slow and long moult that largely overlaps with breeding, and (2) a shorter moult that overlaps less with breeding (both strategies avoid moulting during the cold season). Most Little Swifts (85.7%) moulted their rectrices in a centripetal sequence starting with the outermost pair of rectrices inward. This moult was later in relation to wing feather renewal and had almost no overlap with primary moult. Finally, we tested a method for non‐invasively monitoring moult of small species by collecting and sampling shed feathers without the need to capture the birds themselves, as has been successfully used for larger bird species. This work demonstrates the importance of aerodynamic considerations in the evolution of life‐history traits. Moult‐related aerodynamic costs may be an important evolutionary factor shaping moult strategy, including timing, duration and sequence, mainly among species, like swifts, that are highly dependent on their aerodynamic ability.

Feather wear is the natural degradation and breakage of feather structure during the interval between moults. Different rates of feather wear have been observed for primaries of free‐living populations of several species of passerines and waders, and this variability has been linked to different concentrations of melanins. In this study primary moult duration explained 59% of the variation in annual rates of primary abrasion (percentage wing length loss) of seven Grey Plover wintering populations, while migration distance explained 14%. The analysis suggests that primary moult duration plays a key role in determining primary durability and hence primary quality. Long distance migrants might evolve more durable primaries, despite the higher predation risks and energetic costs of a prolonged moult. Partial or complete pre‐breeding primary moults of first‐year waders and complete biannual moults of some passerines might have evolved under selective forces favouring migration with unabraded primaries.

Examination of 8,141 adult mourning doves (Zenaida macroura) in North and South Carolina revealed that substantial numbers complete primary feather molt in September. Adult mourning doves shed primaries at the rate of 1 per 14 days. No difference was found in this rate between sexes or among years, 1969-74. The initiation of molt differed from year to year, and female molt always preceded male molt. Available data show that southern doves complete primary molt a month earlier than northern doves. Therefore, age based on primary molt can be biased upward if all molt-complete wings from southern hunting samples are considered immature. J. WILDL. MANAGE. 43(1):202-207 Indices of mourning dove reproductive success can be derived from age ratios obtained through hunter bag surveys. This information combined with indices of breeding population size allows biologists to evaluate trends in both population size and annual production. Biologists segregate immature and adult doves by wing plumage characteristics. After the completion of annual wing molt, such identification becomes impossible. Currently, molt-complete doves are considered to be immatures in September, because in a Missouri study of adult mourning dove primary feather molt, 97.5% of the adults had not completed primary molt until October (Sadler et al. 1970). The number of molt-complete doves averaged 6.2% in the Eastern Management Unit Dove Wing Collection Survey for the 1967-70 September hunting seasons (J. L. Rous, pers. comm.). If the Missouri findings do not apply to the entire range of the mourning dove, the possibility of age ratio error exists. This study was undertaken to document adult primary molt in North and South Carolina, examine variability in rate of molt among years and between sexes, predict the earliest dates at which adults complete primary molt, and compare this study's findings with the earlier Missouri study (Sadler et al. 1970). We express our gratitude to R. A. Coon, D. H. Johnson, and R. E. Tomlinson, U.S. Fish and Wildlife Service, and K. C. Sadler, Missouri Department of Conservation, for many helpful suggestions regarding data analysis and manuscript preparation.

Migrant waders using freshwater habitats are hypothesized to have slower primary moult than waders using coastal habitats. We chose the Wood Sandpiper Tringa glareola as a representative species using the freshwater habitats and compare its moult pattern with a range of fresh-water and coastal wader species to test the habitat hypothesis. Only fragmentary descriptions of Wood Sandpipers' primary moult in their sub-Saharan non-breeding quarters had existed. We analysed the primary moult formulae of 1496 adult Wood Sandpipers obtained in southern Africa. The Underhill & Zucchini moult model was used to estimate the timing and duration of moult for all 10 primaries combined and for each primary individually. We also estimated the rate of production of feather material during moult. Adult Wood Sandpipers arrive in southern Africa between late July and November, and depart from mid-March to April. Suspension of moult was observed in 56 birds (7.5%) after two to nine primaries had been replaced. The remaining birds performed a continuous complete primary moult, with average start and completion dates of 21 August and 30 December, respectively; estimated duration was 131 days. The overall rate of production of primary feather material was uniform, achieved by growing up to five small inner primaries simultaneously at the beginning of the moult but only one or two simultaneously while the large outer primaries were growing. Primary moult of adult Wood Sandpipers took longer but ended earlier than in similar-sized waders using coastal habitats. Compared with waders using coastal habitats, Wood Sandpipers prolonged moult by shedding their primaries at longer intervals and by extending the growth period of each primary. The longer primary moult and its earlier ending compared with coastal waders are probably adaptations to Wood Sandpipers' use of freshwater habitats, which in southern Africa provide unpredictable food supplies and might require nomadic movements between ephemeral inland wetlands.

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 biometric and primary moult data housed at the South African Bird Ringing Unit (SAFRING) were analysed for the Sociable Weaver Philetairus socius. The average body mass and wing length was 27.9g (SD = 2.2) and 74.1mm (SD = 2.5), respectively. Variation in these parameters is not clearly correlated with region, season or climate, other than a negative correlation of body mass with average annual water deficiency. Body mass of Sociable Weavers near Kimberley showed a longterm decrease of 2.9g, probably due to stabilising selection on mass. Primary moult duration varied from 152 days to 169 days and started between 26 January and 31 December in two populations (socius and South African eremnus respectively). Individual primaries moulted mainly one at a time, each taking 20–28 days to grow fully. Prolonged moult duration in this species is probably an adaptation to reduce energy expenditure, and to grow more durable feathers due to abrasion in entering the nest. The lack of clear patterns of geographical variation in biometrics indicates that the contiguous populations of Sociable Weaver should belong to the nominate species. The biometric and primary moult data housed at the South African Bird Ringing Unit (SAFRING) were analysed for the Sociable Weaver Philetairus socius. The average body mass and wing length was 27.9g (SD = 2.2) and 74.1mm (SD = 2.5), respectively. Variation in these parameters is not clearly correlated with region, season or climate, other than a negative correlation of body mass with average annual water deficiency. Body mass of Sociable Weavers near Kimberley showed a longterm decrease of 2.9g, probably due to stabilising selection on mass. Primary moult duration varied from 152 days to 169 days and started between 26 January and 31 December in two populations (socius and South African eremnus respectively). Individual primaries moulted mainly one at a time, each taking 20–28 days to grow fully. Prolonged moult duration in this species is probably an adaptation to reduce energy expenditure, and to grow more durable feathers due to abrasion in entering the nest. The lack of clear patterns of geographical variation in biometrics indicates that the contiguous populations of Sociable Weaver should belong to the nominate species.

We investigated the effects of body mass and latitude on primary moult duration from published data of migrating shorebirds that moult exclusively on the wintering grounds. Non‐phylogenetic and phylogenetic models demonstrated that body mass and latitude correlate with moult duration in a non‐additive way: the models predict different latitudinal relationships for smaller and larger shorebirds, and in the northern hemisphere, primary moult duration increased allometrically with body mass (exponent = 0.17), whereas in the southern hemisphere, primary moult duration was not correlated with body mass. If birds optimize feather quality and if slower moult yields sturdier feathers, the fast primary moult of northerly wintering shorebirds indicates additional selection pressures at work.