A Quantitative Analysis of Flight Feather Replacement in the Moustached Tree Swift Hemiprocne mystacea,a Tropical Aerial Forager

The functional life span of feathers is always much less than the potential life span of birds, so feathers must be renewed regularly. But feather renewal entails important energetic, time and performance costs that must be integrated into the annual cycle. Across species the time required to replace flight feather increases disproportionately with body size, resulting in complex, multiple waves of feather replacement in the primaries of many large birds. We describe the rules of flight feather replacement for Hemiprocne mystacea, a small, 60g tree swift from the New Guinea region. This species breeds and molts in all months of the year, and flight feather molt occurs during breeding in some individuals. H. mystacea is one to be the smallest species for which stepwise replacement of the primaries and secondaries has been documented; yet, primary replacement is extremely slow in this aerial forager, requiring more than 300 days if molt is not interrupted. We used growth bands to show that primaries grow at an average rate of 2.86 mm/d. The 10 primaries are a single molt series, while the 11 secondaries and five rectrices are each broken into two molt series. In large birds stepwise replacement of the primaries serves to increase the rate of primary replacement while minimizing gaps in the wing. But stepwise replacement of the wing quills in H. mystacea proceeds so slowly that it may be a consequence of the ontogeny of stepwise molting, rather than an adaptation, because the average number of growing primaries is probably lower than 1.14 feathers per wing.     

The ‘chaotic’ flight feather moult of the Steppe Buzzard Buteo buteo vulpinus

Steppe Buzzards breed in Eurasia and spend the non-breeding season in Africa. Adults moult some flight feathers during the breeding season and some during the non-breeding season. Moult is arrested during migration. The extent of moult of flight feathers in adults is highly variable between individuals in southern Africa, with the renewal of two primaries, three secondaries and five rectrices as the most frequently encountered pattern. Time spent on the non-breeding grounds in South Africa is too short to allow for a sequential moult. Moult of flight feathers is restricted to the almost synchronous dropping of a number of feathers upon arrival, with few being replaced subsequently. Any of the flight feathers can be replaced in southern Africa, and the pattern of renewal in primaries and secondaries cannot be distinguished from random. Tail feathers are replaced in an alternating (transilient) pattern. Moult in the non-breeding areas may primarily be complementary to moult on the breeding grounds, but these two partial moults per year are insufficient to renew all flight feathers annually. Middle secondaries and central tail feathers are regularly carried over to a third moult, but this is rare for primaries.     

The effects of chronic psychological and physical stress on feather replacement in European starlings (Sturnus vulgaris)

Corticosterone (CORT) is seasonally modulated in many passerines, with plasma CORT concentrations lowest during the prebasic molt, when all feathers are replaced. Recent evidence indicating that CORT implants slow the rate of feather regrowth in molting birds suggests that plasma CORT concentrations are downregulated during molt in order to avoid the inhibition of feather growth caused by the protein catabolic activity of CORT. To further test this hypothesis, we examined whether endogenous CORT release, stimulated by exposure to either psychological stress or physical stress (food restriction), could inhibit feather regrowth rates or decrease feather quality in birds undergoing an induced molt (feather replacement after plucking). European starlings (Sturnus vulgaris) were exposed to chronic psychological stress or food restriction for three weeks of the feather regrowth period. Throughout this time, the length of growing primary, secondary, and tail feathers was measured and blood samples were collected to measure baseline and stress-induced CORT concentrations. Upon completion of growth, feather quality was analyzed via measurements of mass, rachis length, feather area, and presence of fault bars. Both psychological and physical stress protocols elevated circulating plasma CORT but significantly less than implants from an earlier study did. Psychological stress had no effect on feather regrowth rates or feather quality. Food restriction had no effect on feather growth rate but caused asynchronous feather replacement. When combined with psychological stress, physical stress also resulted in smaller feather area. Results indicate that CORT implants may not accurately represent chronic stress physiology. Additionally, the purpose for downregulating CORT concentrations during molt appears to be more complicated than simply protecting feather production from CORT's catabolic effects.     

The effects of chronic psychological and physical stress on feather replacement in European starlings (Sturnus vulgaris).

Corticosterone (CORT) is seasonally modulated in many passerines, with plasma CORT concentrations lowest during the prebasic molt, when all feathers are replaced. Recent evidence indicating that CORT implants slow the rate of feather regrowth in molting birds suggests that plasma CORT concentrations are downregulated during molt in order to avoid the inhibition of feather growth caused by the protein catabolic activity of CORT. To further test this hypothesis, we examined whether endogenous CORT release, stimulated by exposure to either psychological stress or physical stress (food restriction), could inhibit feather regrowth rates or decrease feather quality in birds undergoing an induced molt (feather replacement after plucking). European starlings (Sturnus vulgaris) were exposed to chronic psychological stress or food restriction for three weeks of the feather regrowth period. Throughout this time, the length of growing primary, secondary, and tail feathers was measured and blood samples were collected to measure baseline and stress-induced CORT concentrations. Upon completion of growth, feather quality was analyzed via measurements of mass, rachis length, feather area, and presence of fault bars. Both psychological and physical stress protocols elevated circulating plasma CORT but significantly less than implants from an earlier study did. Psychological stress had no effect on feather regrowth rates or feather quality. Food restriction had no effect on feather growth rate but caused asynchronous feather replacement. When combined with psychological stress, physical stress also resulted in smaller feather area. Results indicate that CORT implants may not accurately represent chronic stress physiology. Additionally, the purpose for downregulating CORT concentrations during molt appears to be more complicated than simply protecting feather production from CORT's catabolic effects.     

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.     

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.     

THE MOULT OF REMIGES AND RECTRICES IN GREAT BLACK-BACKED GULLS LARUS MARZNUS AND GLAUCOUS GULLS L. HYPERBOREUS IN ICELAND

The moult of primaries, secondaries, and rectrices in two closely-related gulls, the Great Black-backed Gull Larus mavinus and the Glaucous Gull L. hyperboreus, was studied in Iceland. Both gulls moult their primaries in an extremely regular sequence, starting with the 1st (innermost) and ending with the 10th (oiltermost) feather. Usually two, less often one or three, primaries are growing per wing during the primary moult, which lasts for about six or seven months. Growlng primaries were estimated to lengthen on the average by 8.7 mm per day in marinus and 7.8 mm per day in hyperboreus. The secondaries, usually 24 in number, are shed in two moult waves, one starting with the innermost feather soon after the start of the primary moult and then progressing slowly outwards, the other beginning with the outermost secondary after the primary moult is about half completed and then progressing rapidly inwards. The moult is completed just before the end of the primary moult as the two moult waves meet at about the 16th secondary. There are no marked differences between the two gulls in the moult of secondaries. The moult of rectrices shows large variations in both species, some feathers being much more irregular than others in their time of shedding. In both species, indications of an obscured centrifugal pattern of replacement are seen, although the 5th (next to the outermost) rectrix is usually the last one to be shed. Significant differences were observed between the two species in the degree of regularity of shedding of some feathers and in the average position in the moulting sequence of others. The moult of rectrices starts soon after the moult of primaries is half completed. The feathers are then shed in rapid succession, and the moult is completed some time before the end of the primary moult. The need for good powers of flight at all times is undoubtedly the reason for the protracted primary moult. This in turn causes the moult to start early, in adults sotnetimes before the eggs are laid; immatures moult even earlier than this. The rectrix moult and the main part of the secondary moult do not begin in adults until the young have fledged, but then progress very rapidly. Presumably, the loss of some of these feathers would impair the flying ability to an extent sufficient to make it difficult for the gulls to care for their young, while the rapid moult is necessary in order for the replacement of these feathers to be completed by the time the primary moult is over.     

Temporal and spatial patterns of flight and body feather molt of Bank,Barn, and Cliff swallows in North and South America

Molt is energetically demanding and various molt strategies (i.e., molt series, duration, intensity, timing, and location) have evolved to reduce the negative fitness consequences of this process. As such, molt varies considerably among species. Identifying where and when specific feathers are molted is also crucial to inform species‐specific studies using stable isotope markers to assign individuals to geographical regions where they molt. Using museum specimens, we examined the molt of three species of migratory swallows in the Americas: Bank Swallows (Riparia riparia), Barn Swallows (Hirundo rustica), and Cliff Swallows (Petrochelidon pyrrhonota). All three species have one primary and two secondary molt series. Bank and Cliff swallows had one rectrix molt series, and Barn Swallows molted the outer rectrix (R6) separately from the inner five rectrices (R1‐5). All three species have a relatively long flight feather molt duration (i.e., 140–183 days) and low molt intensity. Barn Swallows initiated flight feather molt in the fall, about 2 months later than Bank and Cliff swallows. Barn Swallows likely delay molt because of constraints associated with double brooding. For all three species, molt started with the primaries and inner secondaries and was closely followed by the rectrices and, finally, the outer secondaries. For those that began and then interrupted molt either in breeding areas or during fall migration, the first feathers molted were predominantly S8 and P1. All three species underwent body molt throughout the year, but most individuals molted their body plumage in wintering areas. We recommend that the most appropriate feathers for stable isotope research examining migratory connectivity and habitat use are either R2‐R4 or S2‐S4.     

Adaptive fault bar distribution in a long‐distance migratory,aerial forager passerine?

Fault bars are translucent bands produced by stressful events during feather formation. They weaken feathers and increase their probability of breakage, and thus could compromise bird fitness by lowering flight performance. It has been recently suggested ('fault bar allocation hypothesis') that birds could have evolved adaptive mechanisms for reducing fault bar load on the feathers with the highest function during flight. We tested this hypothesis by studying first-year individuals of the long-distance migratory, aerial forager barn swallow Hirundo rustica . We predicted that fault bars should be less abundant on the outermost wing and tail feathers, but more frequent on the tail than on the outermost wing feathers. Accordingly, we found that fault bars occurred more often in tertials than in primaries or secondaries. Tail feathers had fewer fault bars than tertials, but more than primaries. Within the tail, the distribution pattern of fault bars was W-shaped, with the highest fault bar load occurring on the streamers and on the two central feathers. Because streamers are the most important tail feathers for flight performance, this finding seems to contradict the 'fault bar allocation hypothesis'. However, flight performance is much less sensitive to changes in the shape of the tail than of the wings, which could explain why evolutionary forces have not counteracted the increase of fault bars associated with feather elongation during the recent evolution of streamers in the tail of hirundines.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 455–461.     

Isotopic evidence for endogenous protein contributions to greylag goose Anser anser flight feathers

Feather stable isotope composition may not reflect local isoscapes in which they were grown if supplemented with protein of endogenous origin. Thus, feather isotope analysis, combined with knowledge of local isoscapes can be used to infer endogenous nutrient composition to feathers in cases where birds travel to moult. We investigated this possibility in a study of flightless moulting greylag geese Anser anser on the Danish island of Saltholm, which are known to mobilise endogenous protein stores (acquired at previous terrestrial staging locations in Sweden) to reconstitute muscle blocks and organs whilst feeding on a saltmarsh (i.e. marine-influenced) diet with contrasting stable isotope ratios. We used stable isotope (δ¹³C, δ¹⁵N) measurements to test the prediction that new-grown flight feathers would have stable isotope values intermediate between those derived from a purely terrestrial C₃ diet and one composed purely of saltmarsh plants. Feather δ¹³C and δ¹⁵N values were intermediate between those expected for feather material derived from local saltmarsh (i.e. exogenous) food items and Swedish terrestrial (endogenous muscle) sources, suggesting a mixing of endogenous and exogenous sources. These results confirm that moult migrant Anatidae exploit body stores to meet specific protein needs during the flightless period of remige regrowth and caution against the use of feather stable isotope ratios as direct indicators of the isotopic environment in which they were regrown, where endogenous contributions may occur.     

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.     

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.     

Exogenous and endogenous corticosterone in feathers

In birds, the steroid hormone corticosterone (CORT) increases in response to real or perceived threats to homeostasis. A long‐term record of CORT exposure is recorded in feathers when the hormone is incorporated into the keratinized tissue, and then preserved when the mature feather is cut off from the blood supply. The opportunity to retrospectively assess the exposure of an individual to stressors by measuring the amount of CORT in a feather has generated excitement amongst avian ecologists. However, this technique is relatively new and requires additional validations. In this study, we performed experiments in wild caught European starlings Sturnus vulgaris to test whether: 1) CORT deposition in the feather depends on time of day and 2) whether an ecologically relevant stressor (unpredictable food access) causes a change in feather CORT. We found that exogenous CORT was incorporated into feathers during the day and the night. However, there was no difference in feather CORT between birds with unpredictable access to food and those with continuous access, indicating that feather CORT might not always detect ecologically relevant stressors.     

House sparrows offset the physiological trade‐off between immune response and feather growth by adjusting foraging behavior

Growing feathers and mounting immune responses are both energetically costly for birds. According to the life history trade‐off hypothesis, it has been posited that the costs of feather growth lead to temporal isolation between molt and other expensive activities, reproduction for example. In contrast to life cycle events, the need to mount an immune response can occur at any time, including during feather growth. Thus, we hypothesized that mounting an immune response during feather growth may divert energy and resources from feather growth and impair feather renewal. To test this hypothesis, we clipped or plucked the same feathers of male house sparrows Passer domesticus biblicus. In the clipped group (n = 16), the feathers were absent with no regrowth; in the plucked group (n = 14), feathers were absent and regrowth was initiated. We also had an intact control group of 15 sparrows. We then initiated an inflammatory immune response by subcutaneous injection over the left breast muscle of the birds with a lipopolysaccharide (LPS) and quantified behavioral and physiological responses. We predicted that sparrows with plucked feathers would incur the highest energetic costs while mounting an immune response, and would increase their foraging effort to offset this cost. We found no difference in body mass and resting metabolic rates among sparrows subjected to the different feather and immune treatments. However, we did find that while sparrows with plucked feathers increased foraging efficiency following the immune challenge by paying fewer but longer visits to the food tray, allowing them to maintain food consumption. Foraging efficiency in sparrows with clipped feathers was reduced. We also found that quality of newly grown feathers after the immune challenge was poorer in the plucked group, suggesting that mounting an immune response competes with feather growth for resources.     

The moult of Barred Warblers Sylvia nisoria in Kenya—evidence for a split wing-moult pattern initiated during the birds' first winter*

The moult of Barred Warblers Sylvia nisoria was studied during three winter seasons in southeastern Kenya at a southward passage site (Ngulia) and a wintering site (Mtito Andei). Most Barred Warblers migrating through Ngulia in November had yet to commence winter moult. These birds probably moulted subsequently in winter in northern Tanzania. In December, birds were found in heavy moult at Mtito Andei, and some of these birds were known to stay throughout the winter. By contrast, most birds reaching southeastern Kenya from late December onwards had already completed part or all of their winter moult, presumably at stopover sites in northern and eastern Kenya or in Ethiopia. Thus, winter moult in Barred Warblers takes place mainly in late November and December, either just before or soon after the final leg of autumn migration. In general, first-year birds renewed all tertials and tail feathers, about three to five secondaries per wing and commonly also the outer one to four large primaries per wing. Adults renewed all tertials and tail feathers, almost all secondaries and only occasionally an outer primary. The replacement of relatively fresh juvenile secondaries during the birds' first winter implies that the split moult pattern of this species (secondaries, tertials and tail moulted in winter; primaries and tertials in summer) is endogenously controlled.     

Moult in Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma

We recorded the age of individual wing and tail feathers of Black-browed and Grey-headed Albatrosses Diomedea melanophris and D. chrysostoma of known age and breeding status at Bird Island, South Georgia. Breeders and non-breeders of both species moult their rectrices annually. Non-breeders moult primaries biennially. In the first year of a cycle, the outer three and some inner primaries are moulted descendantly; in the next year the inner primaries are moulted ascendantly, starting from primary seven. There is a general progression to moulting equal numbers of primaries in each half of the cycle by the time breeding starts at about 10 years of age. Grey-headed Albatrosses usually moult fewer primaries than Black-browed Albatrosses, particularly as 3-year-olds, when they undertake substantial plumage change in body moult. Most secondaries in Black-browed Albatrosses have been replaced once by age 4 years. Breeding Black-browed Albatrosses continue the moult pattern established as immatures whether they fail or not, as do failed Grey-headed Albatrosses. Successful Grey-headed Albatrosses, which breed again 16 months later, moult their three innermost primaries after breeding in the remainder of the current year and, after a period when moult is interrupted, renew the remaining primaries the following year. Comparisons between species and between failed and successful birds within species indicate that moult rate is not closely linked to the length of the interval between breeding attempts. Interspecies differences are better explained by breeding latitude, with tropical albatrosses moulting twice as fast as sub-Antarctic species, possibly reflecting food availability outside the breeding season.     

Sex-dependent frequency and consequences of natural handicaps in American Kestrels

Natural selection theory suggests that there should be fitness consequences for animals that possess morphological abnormalities such as missing or deformed appendages and other structures. As these characters are expected to be detrimental, morphological abnormalities could be considered “handicaps”. However, little information exists about the nature, prevalence or consequences of naturally occurring handicaps in birds, even though experimental handicapping has been used in some behavioural studies. Here, we document and describe the frequency of natural handicaps in American Kestrels Falco sparverius, and investigate their influence on condition and survival. We considered three different categories of handicap that should negatively impact falcons: missing remiges and rectrices, broken remiges and rectrices, and foot handicaps. Broken feathers, followed by missing feathers, were the most common handicaps detected in kestrels and their prevalence increased throughout the breeding season. Foot handicaps were relatively rare and showed no seasonal trends. There was no effect of any handicap type on body condition or return rates of male kestrels. In contrast, females with either foot handicaps or broken feathers were in significantly poorer condition than control females, and females with broken feathers were less likely than control females to return to the study area in years following initial capture. Given that female kestrels with broken feathers have more fault bars than those without broken feathers, and fault bar formation is related to stresses in a bird's past, we suggest that female kestrels that had broken feathers were of poorer quality than those without broken feathers or those with missing feathers. Females with broken feathers may therefore have been in poorer condition initially than other birds, or if broken feathers are indicative of poor quality, then females with broken feathers may have been less able to cope with the negative impacts of feather loss on flight performance compared to birds with missing feathers.     

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.     

Measuring corticosterone in feathers using an acetonitrile/hexane extraction and enzyme immunoassay: feather corticosterone levels of food‐supplemented Atlantic Puffin chicks

Glucocorticoid levels measured in the blood of animals reflect hypothalamic‐pituitary‐adrenal (HPA) activity in response to predictable and unpredictable changes. In birds, circulating corticosterone is incorporated into growing feathers and provides an integrated measure of HPA activity over the period of feather growth. Measuring corticosterone in feathers can provide insight into the physiological state of birds during times when they are unavailable for blood sampling (e.g., during migratory or non‐breeding periods of the annual cycle). Building upon studies that used radioimmunoassay or liquid chromatography, we used a commercially available enzyme immunoassay kit to measure corticosterone in feathers of nestling Atlantic Puffins (Fratercula arctica) on Gull Island, Newfoundland, Canada, in 2012, and demonstrate the benefits of sample preparation via acetonitrile/hexane purification. We used this method to measure corticosterone in feathers of Atlantic Puffin chicks that experienced differences in mass gain in a supplementary feeding study. We found a positive relationship between feather corticosterone and mass gain, and a negative relationship between feather corticosterone and pre‐treatment body condition. Because feathers were growing prior to and during the supplementary feeding period, our results also suggest that extracting seabird feather samples with acetonitrile/hexane (in addition to methanol) prior to measuring corticosterone with enzyme immunoassay is beneficial, and, as reported in previous studies, blood and feather corticosterone values reflect different measures.     

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