A Previously Unknown Plumage of First-Year Indigo Buntings and Theories of Delayed Plumage Maturation
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Abstract First-year, but not adult, Indigo Buntings (Passerina cyanea) have a previously unknown supplemental plumage. The presupplemental molt includes all of the rectrices, the outermost but not the innermost primaries, and, typically, the three innermost secondaries and all body feathers. In this molt, young females exchange one adult-femalelike plumage for another, while young males exchange an adult-femalelike plumage for one that matches that of adult males in winter. Thus, in their first year Indigo Buntings wear: first, the juvenile plumage, the body feathers of which begin replacement before the tail is fully grown; second, the first basic plumage, which in both sexes is entirely femalelike in coloration and includes the juvenile remiges and rectrices; third, the supplemental plumage, assumed either prior to fall migration (<10% of individuals) or on the wintering ground (>90% of individuals) and in which obvious sexual dichromatism is first achieved; and fourth, the first alternate plumage, acquired in a prolonged and often incomplete prealternate molt of body feathers that occurs during February, March, and April on the wintering ground and during the spring in the United States. Because almost all of the femalelike first basic plumage of young males is lost in the presupplemental molt, this plumage almost certainly is an adaptation to conditions encountered either in the fall or early in the first winter. Furthermore, the ensuing supplemental plumage cannot be compromised by color requirements of the first breeding season because of the intervening prealternate molt; thus, the adult-malelike plumage produced by the presupplemental molt likely evolved to meet a change in signaling requirements that occurs in early winter. The signaling function of this plumage is unknown. Because this supplemental plumage of young males resembles the winter plumage of adult males and because all feathers grown by young males in their first prealternate molt resemble those of the adult male breeding plumage, the female mimicry hypothesis of Rohwer et al. (1980) is untenable for the subadult breeding plumage of yearling male Indigo Buntings.Keywords:
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We describe the sequence and extent of the complex and little understood post‐juvenile and post‐breeding moults of Savi's Warblers Locustella luscinioides . In contrast to previous studies, the post‐juvenile moult occurred in at least 44% of the birds, 5% of which moulted some or all tertials and greater coverts. The timing of overlap between the filling and the post‐juvenile moults, and the fact that later‐moulting birds had no post‐juvenile moult, strongly suggests that the moult extent is dependent on fledging date. From July onwards, all adult males overlapped breeding and moult, whereas only 11% of the females did so. The start of moult varied from 6 June to 25 August, and was significantly earlier in males. Only 18% of the birds completed the moult, whereas the remaining individuals retained a variable number of inner primaries and/or secondaries. Interestingly, not only was the number of retained primaries positively associated with the date of moult, but so too was the primary number of birds in which the moult started. We view this as an adaptation allowing the replacement of the most important feathers for flight when the time available for moult is short. Body condition did not vary with the progress of moult when date was taken into account, but fat reserves still tended to decrease and then increase. The body condition was correlated positively with the wing raggedness, so Savi's Warblers do not compensate for an increasing wing load during moult.
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Temporal and energetic constraints associated with migration may compromise plumage quality and, ultimately, flight ability in migratory birds. As a consequence, migrants may invest more resources in parts of the plumage that are essential for long, sustained flight (such as the primary wing feathers) than in less important feather tracts. We used migratory and sedentary Blackcaps (Sylvia atricapilla) to analyze within- and between-individual variation in the mass and quality of wing and tail feathers. Migratory Blackcaps in both adult and juvenile plumage had lighter tail feathers than sedentary Blackcaps, but the primary feathers were of similar mass. Interestingly, the quality of primary and tail feathers (estimated from the mass of the feather in relation to its size) were positively correlated within individuals. However, migratory individuals had higher-quality primary feathers than sedentary individuals, given the quality of their tail feathers. Therefore, migratory Blackcaps appeared to preferentially allocate limited resources to primary feathers at the expense of the quality of the less important tail feathers. We suggest that this represents an adaptive mechanism to reduce the costs of migration constraints on plumage functionality.
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Summary 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.
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Great Grey Owls start flight feather moult when in their second year. Moult was studied on outspread wings of 58 individuals in the collections at Naturhistoriska Riksmuseet in Stockholm. The owls always moulted the innermost secondaries in their first moult, and usually at least two primaries, most often P5 and P6. After this moult, birds had 11–17 juvenile feathers left in each wing, of a total of 21 flight feathers. In their second flight feather moult, birds shed primaries outwards and inwards from the primaries moulted during the first moult. A variable number of secondaries outwards from S10 and S11 were moulted. All birds retained at least one juvenile feather, always P1. The number of juvenile flight feathers after the second moult was 1–6. The collection held no individuals known to be in their third flight feather moult. Thus it was not possible to determine whether birds in this age group could be aged by the wing moult pattern. Great Grey Owls with no juvenile flight feathers should thus be classified as 4C+ in autumn, and 5C+ in spring.
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Moulting is an essential rite of passage for chicks across the globe, disposing of their downy fluff in favour of majestic flight feathers that bear them aloft. But no one knew how these juvenile aviators orchestrate their transformation. As the ubiquitous hormone insulin-like growth factor 1 (IGF-1) is key to growth in many organisms, Ádám Lendvai and colleagues from the University of Debrecen, Hungary, with collaborators from the Institute of Pharmaceutical Sciences, Switzerland, collected juvenile bearded reedlings (Panurus biarmicus) from the Hortobágy-Halastó wetland reserve in Hungary to find out whether a dose of the hormone would help their moult along.Impressively, the youngsters that received an injection of microscopic particles that gradually released IGF-1 into their blood replaced their feathers faster than the birds that had not received the injection. In addition, the injected birds produced more new feathers; their moult was further along. The new feathers were also in better condition and had fewer blemishes than those of the untreated birds. However, when the team compared how fast the young adults’ individual feathers grew, the hormone hadn't increased their growth rate; the feathers of the untreated birds were growing just as fast.‘These results suggest that an increase in IGF-1 does not speed up feather growth, but may alter moult intensity by initiating the renewal of several feathers simultaneously’, says Lendvai. However, the team suspects that IGF-1 isn't the only hormone involved in restoring birds’ plumage. Explaining that stress can suddenly reduce the amount of IGF-1 in a bird's blood – potentially placing them in peril if the drop occurred at a critical point in the moult – Lendvai suspects that other hormones also play an essential role coordinating the transformation of the bearded reedling youngsters from scruffy balls of fluff to perky adult reed bed residents.
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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.
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Yellowhammers caught in North Yorks and Cleveland were photographed concentrating on tail feathers. A plumage feature on the outer tail feathers allowed 97% (n=100) of birds to be aged correctly. During March 5% of birds were noted moulting some tail feathers.
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SummaryThe development of the tail plumage of the female and male Superb Lyrebird Menura novaehollandiae proceeds through a number of moults during which the feathers formed undergo structural changes. The number of barbs in successive 50 mm lengths of the main rectrices (plain and filamentary feathers) (designated ‘barb density’) were counted, starting at the distal end. As the bird grows older, the relevant barb densities decrease. The paper identifies the changes in structure of a feather during the growing process. The case histories of several identifiable subjects are given, illustrating the independent behaviour of the individual follicles within the tail plumage of particular birds and between different birds.
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