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.     

Phenotypic flexibility of a southern African duck Alopochen aegyptiaca during moult: do northern hemisphere paradigms apply?

Phenotypic flexibility during moult has never been explored in austral nomadic ducks. We investigated whether the body condition, organ (pectoral muscle, gizzard, liver and heart) mass and flight‐feather growth Egyptian geese Alopochen aegyptiaca in southern Africa show phenotypic flexibility over their 53‐day period of flightless moult. Changes in body mass and condition were examined in Egyptian geese caught at Barberspan and Strandfontein in South Africa. Mean daily change in primary feather length was calculated for moulting geese and birds were dissected for pectoral muscle and internal organ assessment. Mean body mass and condition varied significantly during moult. Body mass and condition started to decrease soon after flight feathers were dropped and continued to do so until the new feathers were at least two‐thirds grown, after which birds started to regain body mass and condition. Non‐moulting geese had large pectoral muscles, accounting for at least 26% of total body mass. Once moult started, pectoral muscle mass decreased and continued to do so until the flight feathers were at least one‐third grown, after which pectoral muscle mass started to increase. The regeneration of pectoral muscles during moult started before birds started to gain overall body mass. Gizzard mass started to increase soon after the onset of moult, reaching a maximum when the flight feathers were two‐thirds grown, after which gizzard mass again decreased. Liver mass increased significantly as moult progressed, but heart mass remained constant throughout moult. Flight feather growth was initially rapid, but slowed towards the completion of moult. Our results show that Egyptian geese exhibit a significant level of phenotypic flexibility when they moult. We interpret the phenotypic changes that we observed as an adaptive strategy to minimize the duration of the flightless period. Moulting Egyptian geese in South Africa undergo more substantial phenotypic changes than those reported for ducks in the northern hemisphere.     

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.     

The scaling of primary flight feather length and mass in relation to wing shape, function and habitat

The mass and length of each primary flight feather was measured in 120 species of birds (347 individuals) representing 37 families and 15 orders. The scaling relationship between mass and length was determined using the mass of each primary as a proportion of total primary feather mass for that individual and, similarly, length as a proportion of total length. This eliminated errors due to intra- and interspecific differences in absolute size. In every species there was a highly significant constant scaling relationship (log mass/log length) for all of the primary feathers proximal to the feather that formed the wing tip. This relationship was allometric and varied between 1.80 in Rooks Corvus frugilegus and 4.87 in Winter Wrens Troglodytes troglodytes . The mean scaling relationship for 120 species was 2.41 ± 0.42 sd, which was significantly less ( P  < 0.0001) than isometry (i.e. 3.00). In most species (117 of 120) the primary feather forming the wing tip and all feathers distal to it had a different scaling relationship, and had a greater mass than expected from their length. The greater relative mass of the outer primaries may reflect a protective role against physical abrasion, or an aerodynamic role in that each of these feathers provides a leading edge to the wing. Thus, there were two scaling relationships that pivoted about the feather forming the wing tip, resulting in a characteristic 'signature' for each species. Scaling relationships can be related to flight characteristics and habitat, rather than to phylogeny. Closely related species often had widely varying scaling relationships. In general, species exploiting dense vegetation had greater scaling relationships than more aerial species. However, species with a high scaling relationship did not have a greater mean feather mass, so the increased relative mass of the distal primaries was at the expense of proximal primary feather mass.     

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.     

MOULT IN FIVE SPECIES OF CORVIDAE IN BRITAIN

This paper presents objective methods for measuring moult and uses them to describe the pattern and rate of the complete moult as a component of the annual cycle in Corvus corone, C. frugilegus, C. monedula, Pica pica and Garrulus glandarius in Britain. The basis of the methods used to measure the rate of moult was the dry weight of the whole plumage and its component tracts and feathers. Within whole tracts of flight feathers showing diversity of size, the longer feathers grew in length a little faster than the others by accumulating feather material very much faster. Thus, for the flight feathers at least length by itself was a poor indicator of size, but, if first related to weight, could be used to predict weight. Hence, to enable realistic comparisons to be made between different flight feathers and tracts of flight feathers on a given individual bird or on individuals of different species, a ‘units’ system was created which would take account of such variations in size. This information provided a standard against which the growth of new flight feathers in a specimen collected in the field could be measured. The progress of moult in each tract was indicated by the sum of the units. In addition, for both the flight feathers and all other tracts, the duration of moult was measured from the start and finish in each tract as indicated by the proportion of birds having either growing or entirely fully-grown feathers in each tract. In the annual cycle body weight and abdominal fat weight were at a maximum in mid-winter and at a minimum in mid-summer in Corvus; variations in these items were apparently absent in G. glandarius. In Corvus probably only post-second-year birds breed, but in P. pica some second-year individuals do so as well; also, increase in testes size in second-year males was greatest in P. pica. The patterns of the relative seasonal timing of the start and finish of moult in each tract were most similar in the three Corvus species, in which moult in the whole plumage began in the primary tract and finished in tracts on the body; P. pica differed principally in the extended growth of the secondary tract; G. glandarius differed in that moult began in the dorsal tract. By summing the data from individual tracts, a measure of the rate of growth in the whole plumage was obtained: all five species moulted at essentially the same time of year. In the primary, secondary, tertiary and rectricial tracts the seasonal accumulation of dry weight of feather material in each tract followed a sigmoid pattern; in the alula tract dry weight increased most rapidly at the beginning. These patterns were correlated with the numbers of feathers growing at different stages in each tract. The primary tract accumulated dry matter at the highest relative rate, while the rectricial, secondary, tertiary and alula tracts did so at successively lower rates. The maximum relative rate of increase in dry weight in any given tract of flight feathers was fairly similar in all five species, but was possibly related inversely to body weight. Maximum absolute rates of increase in dry tract weight were also calculated. During the springtime period when non-moulting and moulting birds were present simultaneously in the population, no difference could be detected between these groups in any species in body and fat weights; in individuals obtained together with evidence of reproductive activity, few had begun primary moult, but in post-second-year C. frugilegus with branchers, males began before females; in C. corone and C. frugilegus testes weight was lower in moulting than in non-moulting birds. In conclusion, some aspects of moult for further research are suggested.     

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.     

Relationships among timing of moult,moult duration and feather mass in long‐distance migratory passerines

Moult is a costly but necessary process in avian life, which displays two main temporal patterns within the annual cycle of birds (summer and winter moult). Timing of moult can affect its duration and consequently the amount of material invested in feathers, which could have a considerable influence on feather structure and functionality. In this study, we used two complementary approaches to test whether moult duration and feather mass vary in relation to the timing of moult. Firstly, we conducted a comparative study between a sample of long‐distance migratory passerine species which differ in moult pattern. Secondly, we took advantage of the willow warbler's Phylloscopus trochilus biannual moult, for which it is well‐known that winter moult takes longer than summer moult, to assess between‐moult variation in feather mass. Our comparative analysis showed that summer moulting species performed significantly shorter moults than winter moulters. We also detected that feathers produced in winter were comparatively heavier than those produced in summer, both in between‐species comparison and between moults of the willow warbler. These results suggest the existence of a trade‐off between moult speed and feather mass mediated by timing of moult, which could contribute to explain the diversity of moult patterns in passerines.     

Annual survival of Gurney's Sugarbird,Promerops gurneyi

Seasonal variation in body mass and wing length, and the onset and duration of primary moult, were investigated for Chestnut Weavers from northern Namibia. Body mass of adult males was 31.2g (SD 2.6), and adult females weighed 27.4g (SD 1.9). Body mass declined from March to April, and started increasing after August (i.e. near the end of moult) in males and females. Wing length in adult males with new primaries (Oct–Feb) was 80.7mm (SD 2.7) and for adult females (Oct–Feb) 76.8mm (SD 2.6). For both sexes wing length declined during and after the breeding season, due to extensive feather wear. Adult males started primary moult significantly earlier than females (9 April vs 30 April) and moult lasted longer (206 days vs 189 days). The peak summer rainfall and the start of primary moult was earliest in 2000 and latest in 2004 for males and females. Individual primary feathers took 11–18 days to grow.     

Co‐infections by malaria parasites decrease feather growth but not feather quality in house martin

During moult, stressors such as malaria and related haemosporidian parasites (e.g. Plasmodium and Haemoproteus) could affect the growth rate and quality of feathers, which in turn may compromise future reproduction and survival. Recent advances in molecular methods to study parasites have revealed that co‐infections with multiple parasites are frequent in bird–malaria parasite systems. However, there is no study of the consequences of co‐infections on the moult of birds. In house martins Delichon urbica captured and studied at a breeding site in Europe during 11 yr, we measured the quality and the growth rate of tail feathers moulted in the African winter quarters in parallel with the infection status of blood parasites that are also transmitted on the wintering ground. Here we tested if the infection with two haemosporidian parasite lineages has more negative effects than a single lineage infection. We found that birds with haemosporidian infection had lower body condition. We also found that birds co‐infected with two haemosporidian lineages had the lowest inferred growth rate of their tail feathers as compared with uninfected and single infected individuals, but co‐infections had no effect on feather quality. In addition, feather quality was negatively correlated with feather growth rate, suggesting that these two traits are traded‐off against each other. We encourage the study of haemosporidian parasite infection as potential mechanism driving this trade‐off in wild populations of birds.     

两种山鹪莺的春季换羽及尾羽变化

换羽是鸟类为保证持续生存的重要过程。换羽策略与鸟类进化及对环境的适应紧密相关,研究鸟类换羽特征,对于了解鸟类的分类、系统发育、进化历史及其对环境的适应性等方面都有重要意义。2007年3月至9月,在广东肇庆市江溪村对黄腹山鹪莺(Prinia flaviventris)和纯色山鹪莺(P.inornata)的春季换羽进行了研究。通过设置雾网捕捉2种山鹪莺,对捕捉到的成体进行体重及身体量度的测量;对飞羽及尾羽进行标记:初级飞羽以翅尖的第一枚羽毛标记为"P1",次级飞羽以翅中部最外一枚标记为"S1",向内依次递增标记;尾羽以中央两根最长尾羽为"T1",分别向两侧递增标记为"T2~T5"。采用单因素方差分析(One way ANOVA)对不同月份山鹪莺的体重值进行差异性检验,对体重与月份进行Pearson相关分析,对尾羽的长度和宽度进行Pearson偏相关分析(控制变量:体长)。研究结果表明:1)两种山鹪莺换羽期为3至5月,持续时间约为60 d;2)两种山鹪莺春季换羽仅更换尾羽,换羽模式均为离心型,即中央一对尾羽最先开始替换,然后向两侧由内到外逐次更替;3)两种山鹪莺的尾羽长度和宽度同步变化,但绝大部分山鹪莺非繁殖期尾羽长度与繁殖期尾羽长度之比大于非繁殖期尾羽宽度与繁殖期尾羽宽度之比,即繁殖期尾羽相对较宽;4)两种山鹪莺换羽期间体重大致呈现下降趋势,但变化不显著(P0.05)。推测两种山鹪莺通过增加食物的摄入来抵抗换羽期和繁殖期重叠而导致的能量消耗,这可能与该地区丰富的食物资源有关,并在一定程度上体现了两种山鹪莺换羽策略对环境的适应性。     

Body mass and latitude both correlate with primary moult duration in shorebirds

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.     

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.     

Large‐scale longitudinal climate gradient across the Palearctic region affects passerine feather moult extent

Large‐scale spatial gradients of environmental conditions shape organisms, populations and ecosystems. Even though environmental gradients are a key research theme in macro‐ecology and biogeography, the effects of large‐scale, east–west, environmental gradients are largely overlooked compared with north–south gradients. Our study focused on feather moult, an important and energy demanding process in birds. By comparing Western and Eastern Palearctic populations of 21 species, we found that juvenile passerines in the Western and Eastern Palearctic differ in the number of feathers moulted as part of their post‐juvenile moult. This difference is most likely the result of a large‐scale climatic gradient in cold season duration and consequent differences in the time available for moulting. Eastern populations were characterized by a limited extent of feather moult that was additionally affected by migration distance and body mass. The longer migration distance in the Eastern Palearctic caused a generally less extensive moult while high body mass was correlated with a low difference in moult extent between the Western and Eastern Palearctic regions. These results highlight the importance of linking annual cycle processes at the organismal level to the specific environmental conditions within the distribution range of each species.     

Ptilochronology proves unreliable in studies of nestling Pied Flycatchers

Ptilochronology does not appear to be a reliable measure of the daily growth rate of contour feathers or the nutritional state of nestling Pied Flycatchers Ficedula hypoleuca . Growth bars on primary remiges, which according to ptilochronology represent a day's increment of feather growth, are only about half as wide as the actual daily increase in the length of these feathers while they are growing. The average width of the growth bars on primaries was also uncorrelated with other commonly used measures of growth or nutritional status (increase in body mass or in the size of the wing or tarsus), although these were highly correlated with each other. In adult flycatchers, the average width of the growth bars on tertials was unrelated to the average bar width on greater coverts, although both feathers are replaced during the winter (prenuptial) moult. This suggests that the growth bars either do not reflect the nutritional status of adults during normal periods of moult or that contour feathers in different tracts vary in their sensitivity to the nutritional status of the moulting bird. To our knowledge, this is the first time that anyone has attempted to apply ptilochronology to nestlings. It is noteworthy that a method of measuring growth and nutritional state that has shown promise when applied to induced feathers of adult birds seems to be unreliable when applied to the developing plumage of nestlings, and perhaps the normal (not-induced) replacement plumage of adults.     

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.     

Of 11 candidate steroids,corticosterone concentration standardized for mass is the most reliable steroid biomarker of nutritional stress across different feather types

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Effect of manipulating feathers of laying hens on the incidence of feather pecking and cannibalism

Feather pecking is a problem in commercial laying hens, particularly in loose-housing systems, where many hens can be affected by only a few feather peckers. In addition, feather pecking can become an even larger problem if it spreads throughout the flock. There are several possible ways that feather pecking may spread. The simplest way is that one hen may damage the feathers of a hen, and another hen may find the damaged feathers an attractive pecking target. The aim of this experiment was to determine if damaged feathers were feather-pecked more than undamaged feathers on the same body area, and to determine whether some types of feather-body area manipulations were preferred over others as pecking stimuli. Manipulations involved damaging the feathers on the rump, tail or belly of different hens, with two or three levels of severity of manipulation at each body area. Sixteen groups of 11 Lohmann Brown hens between 26 and 28 weeks were observed with the recipient, the feather pecker and the body area that was pecked all being recorded. The feather pecks were classified separately as either gentle or severe. Damaged feathers received significantly more severe feather pecks than undamaged feathers. There were also more gentle feather pecks to damaged feathers, although this did not reach statistical significance. The feather-body area manipulations that received the greatest number of severe feather pecks were the tail feathers when they were cut very short, the rump feathers when they were trimmed, and the rump when feathers were removed. These results support the suggestion that feather pecking does indeed spread through flocks by damaged feathers becoming an attractive target for feather-pecking behaviour. An unexpected result of performing the feather manipulations was an outbreak of cannibalism in half of the experimental groups. Even though there was no visible damage to the skin of the hens after having the feathers manipulated, 13 of the 16 attacked hens were wounded on the part of the body where the feathers had been damaged in some way.     

Moulting strategies of a long-distance migratory seabird, the Mediterranean Cory's Shearwater Calonectris diomedea diomedea

Seabird moult is poorly understood because most species undergo moult at sea during the non-breeding season. We scored moult of wings, tail and body feathers on 102 Mediterranean Cory's Shearwaters Calonectris diomedea diomedea accidentally caught by longliners throughout the year. Primary renewal was found to be simple and descendant from the most proximal (P1) to the most distal (P10) feather. Secondaries showed a more complex moulting pattern, with three different asynchronous foci: the first starting on the innermost secondaries (S21), the second on the middle secondaries (S5) and the latest on the outermost secondaries (S1). Rectrix moult started at a later stage and was simple and descendant from the most proximal feather (R1) expanding distally. Although a few body feathers can be moulted from prelaying to hatching, moult of ventral and dorsal feathers clearly intensified during chick rearing. Different moulting sequences and uncoupled phenology between primary and secondary renewal suggest that flight efficiency is a strong constraint factor in the evolution of moulting strategies. Moreover, moult of Cory's Shearwaters was synchronous between wings and largely asynchronous between tail halves, with no more than one rectrix moulted at once. This result is probably related to the differential sensitivity of wings and the tail on flight performance, ultimately derived from different aerodynamic functions. Finally, Cory's Shearwater females renewed feathers earlier and faster than males, which may be related to the lower chick attendance of females.