Increase of feather quality during moult: a possible implication of feather deformities in the evolution of partial moult in the great tit Parus major

Here we investigate the change in feather quality during partial post‐juvenile and complete post‐breeding moult in great tit Parus major by measuring the change in the number of fault bars and feather holes on wing and tail feathers. Feathers grown during ontogeny usually are of lower quality than feathers grown following subsequent moults at independence. This is reflected by higher number of fault bars and feather holes on juveniles compared to adults. Fault bars are significantly more common on tail and proximal wing feathers than on the distal remiges, indicating a mechanism of adaptive allocation of stress induced abnormalities during ontogeny into the aerodynamically less important flight feathers. On the contrary, feather holes produced probably by chewing lice have a more uniform distribution on wing and tail feathers, which may reflect the inability of birds to control their distribution, or the weak natural selection imposed by them. The adaptive value of the differential allocation of fault bar between groups of feathers seems to be supported by the significantly higher recapture probability of those juvenile great tits which have fewer fault bars at fledging on the aerodynamically most important primaries, but not on other groups of flight feathers. The selection imposed by feather holes seems to be smaller, since except for the positive association between hatching date, brood size and the number of feather holes at fledging, great tits' survival was not affected by the number of feather holes. During post‐juvenile moult, the intensity of fault bars drops significantly through the replacement of tail feathers and tertials, resulting in disproportional reduction of the total number of fault bars on flight feathers related to the number of feathers replaced. The reduction in the number of fault bars during post‐juvenile moult associated with their adaptive allocation to proximal wing feathers and rectrices may explain the evolution of partial post‐juvenile moult in the great tit, since the quality of flight feathers can be increased significantly at a relatively small cost. Our results may explain the widespread phenomenon of partial post‐juvenile moult of flight feathers among Palearctic passerines. During the next complete post‐breeding moult, the total number of fault bars on flight feathers has remained unchanged, indicating the effectiveness of partial post‐juvenile moult in reducing the number of adaptively allocated fault bars. The number of feather holes has also decreased on groups of feathers replaced during partial post‐juvenile moult, but the reduction is proportional with the number of feathers moulted. In line with this observation, the number of feather holes is further reduced during post‐breeding moult on primaries and secondaries, resulting in an increase in feather quality of adult great tits.     

Late‐moulting Black‐necked Grebes Podiceps nigricollis show greater body mass in the face of failing food supply

From August to December, thousands of Black‐necked Grebes Podiceps nigricollis concentrate during the flightless moult period in salt ponds in the Odiel Marshes, southern Spain, where they feed on the brine shrimp Artemia parthenogenetica. We predicted that because Black‐necked Grebes moulted in a food‐rich, predator‐free environment, there would be no net loss of body mass caused by the use of fat stored to meet energy needs during remigial feather replacement (as is the case for some other diving waterbirds). However, because the food resource disappears in winter, we predicted that grebes moulting later in the season would put on more body mass prior to moult because of the increasing risk of an Artemia population crash before the moult period is completed. Body mass determinations of thousands of birds captured during 2000–2010 showed that grebes in active wing‐moult showed greater mass with date of capture. Early‐moulting grebes were significantly lighter at all stages than late‐moulting birds. Grebes captured with new feathers post‐moult were significantly lighter than those in moult. This is the first study to support the hypothesis that individual waterbirds adopt different strategies in body mass accumulation according to timing of moult: early‐season grebes were able to acquire an excess of energy over expenditure and accumulate fat stores while moulting. Delayed moulters acquired greater fat stores in advance of moult to contribute to energy expenditure for feather replacement and retained extra stores later, most likely as a bet hedge against the increasing probability of failing food supply and higher thermoregulatory demands late in the season. An alternative hypothesis, that mass change is affected by a trophically transmitted cestode using brine shrimps as an intermediate host and Black‐necked Grebes as final host, was not supported by the data.     

Adventitious feather replacement favours a more rapid regeneration of primaries over rectrices in two passerine bird species

There is increasing evidence of adaptive preferential investment during moult in those feather tracts that are more advantageous for fitness. In this study, we assessed whether, after the manual removal of two functionally different flight feathers (one primary and one rectrix), birds from two common passerine species (Eurasian Blackcap Sylvia atricapilla and European Robin Erithacus rubecula) favoured the regeneration of primary (supposedly the most functionally important feathers) over rectrix feathers. Our results did not show differences between replaced primary and rectrix feathers in their final length, but demonstrated that the gap left by the loss of the primary feather was filled earlier, suggesting that a rapid repair of the most essential feather tracts is also evolutionarily advantageous during the adventitious replacement of plumage.     

Experimental evidence that a large raptor can detect and replace heavily damaged flight feathers long before their scheduled moult dates

Because many species of large birds must remain capable of flight during moult and breeding, complete replacement of all flight feathers often takes two or more years, with the result that their plumage normally includes many faded, worn and sometimes even broken feathers. It seems adaptive for such birds to have the ability to quickly replace severely damaged feathers. In search of such a feather replacement mechanism, we cut rectrices on a captive Golden Eagle Aquila chrysaetos and found that feathers cut in their first year of use were replaced, on average, after 11.4 months, whereas uncut feathers before and during the experiment were moulted, on average, after 24 months of use. Feather cutting advanced moult, on average, in excess of a year and thereby demonstrates the existence of a previously undescribed neurophysiological mechanism for preferentially replacing damaged feathers.     

Age‐specific variation in relationship between moult and pre‐migratory fuelling in Wood Sandpipers Tringa glareola in southern Africa

Trans‐equatorial avian migrants tend to breed, moult and migrate – the main energy‐requiring events in their lifecycle – at different times. Little is known about the relationship between wing moult and pre‐migratory fuelling in waders on their non‐breeding grounds, where time is less constrained than during their brief high‐latitude breeding season. We determined age‐related strategies of Wood Sandpipers Tringa glareola to balance the energetic demands of primary moult against pre‐migratory fuelling in southern Africa by analysing body mass and primary moult at first capture of 1721 birds mist‐netted in 1972–96 at waterbodies in Zimbabwe. Adults moulted all their primaries in August–December, but immatures underwent a supplemental moult of varying numbers of outer primaries in December–April, close to departure. We used locally weighted linear regression to estimate trends in Wood Sandpiper body mass from 1 July to 1 May. They maintained low mass from arrival in July–September to February–early March. Adults fuelled from 10 February to 1 May at a mean rate of 0.25 g/day (sd = 0.16). Most adults (98%) began fuelling 10–75 days after completing primary moult. Immatures fuelled from 4 March to 13 April at 0.24 g/day (sd = 0.14). They used varying strategies depending on their condition: a brief gap between moult and fuelling; an overlap of these processes near departure, leading to slower fuelling; or skipping fuelling altogether and staying in southern Africa for a ‘gap year’. Immatures moulting three or five outer primaries fuelled more slowly than post‐moult birds. Immatures moulting four outer primaries started fuelling 3 weeks later but at a higher rate than did post‐moult birds of this group. In post‐moult immatures, the later they ended moult, the later and faster they fuelled. The heaviest adults and immatures using all moult patterns accumulated fuel loads of c. 50% of lean body mass, and could potentially cross 2397–4490 km to reach the Great Rift Valley in one non‐stop flight. Immatures were more flexible in the timing and extent of moult and in the timing and rate of fuelling than adults. This flexibility enables inexperienced Wood Sandpipers to cope with inter‐annual differences in feeding conditions at Africa's ephemeral inland waterbodies.     

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.     

Mechanical and structural adaptations to migration in the flight feathers of a Palaearctic passerine

Current avian migration patterns in temperate regions have been developed during the glacial retreat and subsequent colonization of the ice‐free areas during the Holocene. This process resulted in a geographic gradient of greater seasonality as latitude increased that favoured migration‐related morphological and physiological (co)adaptations. Most evidence of avian morphological adaptations to migration comes from the analysis of variation in the length and shape of the wings, but the existence of intra‐feather structural adjustments has been greatly overlooked despite their potential to be under natural selection. To shed some light on this question, we used data from European robins Erithacus rubecula overwintering in Campo de Gibraltar (Southern Iberia), where sedentary robins coexist during winter with conspecifics showing a broad range of breeding origins and, hence, migration distances. We explicitly explored how wing length and shape, as well as several functional (bending stiffness), developmental (feather growth rate) and structural (size and complexity of feather components) characteristics of flight feathers, varied in relation to migration distance, which was estimated from the hydrogen stable isotope ratios of the summer‐produced tail feathers. Our results revealed that migration distance not only favoured longer and more concave wings, but also promoted primaries with a thicker dorsoventral rachis and shorter barb lengths, which, in turn, conferred more bending stiffness to these feathers. We suggest that these intra‐feather structural adjustments could be an additional, largely unnoticed, adaptation within the avian migratory syndrome that might have the potential to evolve relatively quickly to facilitate the occupation of seasonal environments.     

Using stable isotope analysis to determine the winter moult extent in migratory birds: the complex moult of Savi's warblers Locustella luscinioides

Patterns of feather wear in birds captured in spring have traditionally been analysed to describe the extent of winter moult in long‐distance migrants. However, the interpretation of feather wear may be rendered extremely difficult due to long moult periods, by the progress of the season, and by the existence of complex moult patterns. Here, stable isotope analysis is used to determine the origin of the wing feather generations present in Savi's warblers Locustella luscinioides captured in Portugal. Carbon, nitrogen and hydrogen isotope ratios of feathers of known European origin differed significantly from those known to have grown in Africa. A discriminant analysis, in which 91.1% of the cross validated samples were correctly classified, was used to determine the origin of tail and wing feathers collected from birds caught when they returned to the breeding quarters. The interpretation of feather‐wear generally agreed with the stable isotope analysis, but some inconsistencies were identified. The extent of winter moult in Savi's warblers is described and its moult strategy discussed.     

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.     

Moult in the Loggerhead Shrike Lanius ludovicianus is influenced by sex,latitude and migration

We investigated moult strategies in Loggerhead Shrikes by examining first prebasic or preformative moult patterns and by assessing the general location where individual feathers were grown using stable hydrogen isotope (δ²H) analysis. We tested the relative importance of factors known to impact moult timing and pattern, including age, sex, body size, food availability and migration. Migratory Shrikes showed evidence of suspended moult, in which feathers are moulted on both the breeding and the non‐breeding grounds with a suspension of moult during migration. Extent of moult was best explained by sex, longitude, migratory behaviour and breeding‐ground latitude. Male Hatch Year (HY) Shrikes replaced more feathers on the breeding grounds prior to migration than did HY females and moulted more extensively on the breeding grounds than did females. Non‐migratory HY Shrikes underwent a more extensive preformative moult than migratory HY Shrikes. Individuals in more southerly migratory populations moulted more extensively on the breeding grounds than did those breeding further north. Our data also indicate that individuals in the northeastern populations moulted more extensively on the breeding grounds than did those in the north and southwest. Our study underlines the complex structure and variation in moult possible within species, revealing surprising levels of differentiation between sexes and age cohorts, linked to environmental factors on the breeding grounds. Our study highlights the utility of an intrinsic marker, specifically δ²H analysis, to test hypotheses regarding the evolutionary and ecological forces driving moult. Although the methodology has not commonly been applied to this area of research, our results indicate that it can provide unprecedented insight into inter‐ and intra‐specific adaptive response to constraints, whereby individuals maximize fitness.     

THE MOULT OF THE WHITE-BACKED AND RÜPPELL'S GRIFFON VULTURES GYPS AFRICANUS AND G. RUEPPELLII

Moult is continuous throughout the life of the White-backed Vulture and Rüppell's Griffon Vulture. Primary feather moult starts about 10 months after the bird leaves the nest, and the first feather to be shed is the innermost primary. From this position primary moult proceeds in an orderly sequence outwards towards the tip of the wing. Secondary feather replacement does not occur by the progression of moult waves, but by the irregular growth of feathers. It probably takes about 3 years of moult activity to complete the first feather replacement. Subsequent feather replacements occur by a slow but continuous process of feather replacement. Birds in adult plumage do show variations in the speed of moult, but this could not be related to breeding or body condition.     

Factors influencing the evolution of moult in the non‐breeding season: insights from the family Motacillidae

The number of moults per annual cycle and their final spatial pattern (i.e. topography) show high interspecific variation in the order Passeriformes. Factors behind this variability remain obscure, especially for variability in spatial pattern among species. Here, we explored the relative influence of ten ecological, ontogenetic, social and sexual factors on the evolution of autumn moult (feather replacement largely undertaken by migratory species, which is not necessarily an independent episode within their moult cycle) and prealternate moult among Northern Hemisphere species of the family Motacillidae using phylogenetically controlled analyses, ancestral state reconstruction and analyses of correlated evolution. The results strongly support the presence of prealternate moult and absence of autumn moult as ancestral states in this family. A high rate of change between related species indicates phylogenetic independence among prealternate moult patterns and examined factors. Migration distance and gregariousness are the most important factors influencing prealternate moult evolution, and point toward natural selection and sociality as the most important evolutionary drivers of prealternate moult in Motacillidae. Breeding latitude, seasonal plumage change, winter plumage conspicuousness, sexual dichromatism, plumage maturation and extent of preformative moult show a minor influence, and suggest that ontogeny and sexual selection may have played a limited role in shaping prealternate moult in Motacillidae.     

Contrasting strategies for wing‐moult and pre‐migratory fuelling in western and eastern populations of Common Whitethroat Sylvia communis

Trade‐offs between moult and fuelling in migrant birds vary with migration distance and the environmental conditions they encounter. We compared wing moult and fuelling at the northern and southern ends of migration in two populations of adult Common Whitethroats Sylvia communis. The western population moults most remiges at the breeding grounds in Europe (e.g. Poland) and migrates 4000–5000 km to western Africa (e.g. Nigeria). The eastern population moults all remiges at the non‐breeding grounds and migrates 7000–10 000 km from western Asia (e.g. southwestern Siberia) to eastern and southern Africa. We tested the hypotheses that: (1) Whitethroats moult their wing feathers slowly in South Africa, where they face fewer time constraints than in Poland, and (2) fuelling is slower when it coincides with moulting (Poland, South Africa) than when it occurs alone (Siberia, Nigeria). We estimated moult timing of primaries, secondaries and tertials from moult records of Polish and South African Whitethroats ringed in 1987–2017 and determined fuelling patterns from the body mass of Whitethroats ringed in all four regions. The western population moulted wing feathers in Poland over 55 days (2 July–26 August) at a varying rate, up to 13 feathers simultaneously, but fuelled slowly until departure in August–mid‐September. In Nigeria, during the drier period of mid‐February–March they fuelled slowly, but the fuelling rate increased three‐fold in April–May after the rains before mid‐April–May departure. The eastern population did not moult in Siberia but fuelled three times faster before mid‐July–early August departure than did the western birds moulting in Poland. In South Africa, the Whitethroats moulted over 57 days (2 January–28 February) at a constant rate of up to nine feathers simultaneously and fuelled slowly from mid‐December until mid‐April–May departure. These results suggest the two populations use contrasting strategies to capitalize on food supplies before departure from breeding and non‐breeding grounds.     

Chronic coccidian infestation compromises flight feather quality in house sparrows Passer domesticus

Parasites usurp indispensable resources for birds during a moult, and this is particularly relevant for those parasites residing in host intestines. This might compromise the nutritionally demanding moult and, thus, feather functionality. Although lower feather quality has profound and multifaceted adverse effects on residual fitness, surprisingly, little is known about parasites' effect on feather traits, especially over the longer term. We conducted an aviary experiment by medicating half of a group of naturally infested house sparrows Passer domesticus against intestinal coccidians for 15 months, spanning two consecutive postnuptial moults, whereas the other half was kept infested (i.e. without medication). Coccidian infestation significantly and negatively affected the size of the uropygial gland during the second moulting period compared to the medicated group. Furthermore, wing length was significantly shorter after the second moulting in the non‐medicated compared to the medicated female birds, which indicates that the negative effects of coccidians emerge only after a prolonged exposure to parasite infestation. Non‐medicated birds grew poorer quality flight feathers detected in a large number of feather traits both after the first and second moults. In the case of non‐medicated birds, the primaries were lighter and shorter, and had a smaller vane area, thinner rachis and decreased stiffness, although a higher barb and barbule density, which may have various consequences for fitness through reducing flight performance. Our findings demonstrate that, besides the well‐known immediate consequences for host breeding success, parasites might also have serious, long‐lasting effects through influencing feather quality and, ultimately, fitness of the host. © 2013 The Linnean Society of London     

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.     

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.     

Migratory behaviour affects the trade-off between feather growth rate and feather quality in a passerine bird

Migratory birds have less time for moulting than sedentary birds, which may force them to produce their feathers faster at the expense of reducing feather quality. However, the effects of migration on the trade-off between moult speed and plumage quality remain to be studied in natural populations. We analysed the relationship between growth rate and quality of individual feathers, taking advantage of natural variation between migratory and sedentary populations of blackcaps Sylvia atricapilla . As predicted by life-history theory, individual blackcaps showed variable individual quality, which was revealed by positive correlations between feather growth rate and feather mass within populations. However, migrants grew up their feathers faster, producing lighter feathers than sedentary blackcaps. These results support the idea that feather growth rate and feather quality are traded against each other in blackcaps. Such a trade-off is apparently caused by different selection associated to migratory and sedentary life styles, which opens new insights into the diversification of moult patterns in birds.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 98–105.     

Non‐breeding Cackling,Ross's and Snow Geese on Baffin Island show no loss of body mass during wing moult

Non‐breeding Cackling Branta hutchinsii, Ross's Anser rossii and Lesser Snow Geese Anser caerulescens caerulescens captured during remigial moult on Baffin Island in 2015 showed no loss of body mass with moult stage, and individual variation in mass was largely explained by sex and measures of body size (tarsus length). Exceptional conditions in 2015 resulted in almost no reproductive effort or success in that year, so captured geese of all three species were likely to have been non‐breeding individuals that initiated moult early, whereas there were almost no failed or successful breeders, which would normally moult later. This suggests that in a non‐breeding year (i.e. in the absence of competition from large numbers of goslings), locally moulting geese can obtain sufficient exogenous energy to meet their needs during the flightless wing moult period without losing body mass. This also is consistent with the hypothesis that in other species of geese, accumulation of fat stores prior to, and depletion of such stores during, wing moult is adaptive and likely to be a feature of individual plasticity to meet particular needs, such as undertaking moult migration to remote sites where precise foraging and predation conditions cannot be anticipated, or where competition from more dominant individuals may restrict their access to a reliable food supply.     

Wing moult and mass change in free‐living mallard Anas platyrhynchos

Captured free‐living male mallard Anas platyrhynchos at Abberton in southern Britain showed peak mass gain immediately prior to simultaneous remex moult. Individuals of both sexes were heavier before shedding wing feathers than when flightless confirming literature accounts that show mallard accumulate fat stores in anticipation of moult to contribute to meeting energy needs during remex re‐growth. Over the course of four seasons, males lost 13 17% of initial body mass on average during re‐growth of flight feathers, females 13 23%. Based on energy expenditure of 1.3 times BMR, male mallard were estimated to be able to fulfil 42 60% and females 41 82% of their energy needs throughout moult from stores. Free‐flying male mallard fed ad libitum in a predator‐free environment did not differ in starting body mass or rate of mass loss during wing moult compared to free‐living Abberton birds, suggesting depletion of fat stores, irrespective of available sources of exogenous energy. Based on this evidence, we reject that the hypotheses that mass loss in moulting mallard is due to 1) simple energy stress and 2) restrictions on feeding and consider that 3) attaining the ability to fly at an earlier stage on incompletely grown flight feathers is not the primary factor shaping this trait. Rather, we consider the accumulation and subsequent depletion of fat stores, together with reductions in energy expenditure, enable mallard to re‐grow feathers as rapidly as possible by exploiting habitats that offer safety from predators, but do not necessarily enable them to balance energy budgets during the flightless period of remex feather re‐growth.     

Winter body condition in relation to age,sex and plumage ornamentation in a migratory songbird

Winter body condition may play important roles in the life history of migratory birds, but it is difficult to estimate. We used the growth rate of winter‐grown tail feathers of Collared Flycatchers Ficedula albicollis as an indicator of winter body condition, comparing this trait between age classes and sexes and relating it to plumage ornamentation (forehead and wing patch sizes). Adults and males were in better nutritional condition during winter, as indicated by their faster tail feather growth rates, than were yearlings and females, respectively, which could indicate differences in individual quality and foraging ability with age, or age‐ and sex‐related winter habitat segregation. However, feather growth rate was related neither to the size of the winter‐grown forehead patch nor to the size of the summer‐grown wing patch, suggesting weak condition‐dependence for the winter‐grown ornament and complex life‐history consequences for the summer‐grown ornament.