Molt strategy and delayed plumage maturation in the Lined Seedeater
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Abstract:
Lined Seedeaters Sporophila lineola, an intra-tropical migratory songbird, exhibit extensive phenotypic variation, with characteristic black-and-white male and brownish female plumages. In this study, we investigated whether variation in male plumage represents delayed plumage maturation, as reported for many other Sporophila seedeaters. We used data on molt and plumage from a seven-year-long study of color-banded Lined Seedeaters in southeastern Brazil. We also gathered molt and plumage data from museum collections and citizen-science platforms to identify which molts occur outside the breeding grounds. Our findings show that Lined Seedeaters follow a complex basic strategy, but the possibility that some individuals exhibit a complex alternate strategy, which is a common strategy among congeners, cannot be ruled out. Preformative molt and fresh formative plumage were recorded within the breeding grounds in the last months of the breeding season. Prebasic molt also start on the breeding grounds and probably continue during migration to the wintering grounds. Observed phenotypic variation in plumage of Lined Seedeater males is a product of delayed plumage maturation. Breeding males in female-like plumage are formative individuals in their first breeding season. All monitored males acquired black-and-white definitive plumage after their first breeding season, during the second pre-basic molt, but we found limited evidence that some individuals may retain the brownish plumage for more than one cycle. Descriptions presented here advance our understanding of Sporophila molt strategies that can be used in future studies focusing on the evolutionary and ecological underpinnings of plumage variation.Keywords:
Plumage
We investigated mating patterns of the least auklet, a small monogamous seabird, at St. Paul Island, Alaska, during three breeding seasons. Least auklets mated assortatively with respect to both plumage color, a trait important in status signaling, and tarsus length, an index of body size. Least auklets mated disassortatively with respect to the extent of facial plumes, but neither assortatively nor disassortatively for any other ornamental trait (bill color, bill ornament size). Mate fidelity was lower in least auklets than in some long-lived seabird species; when both members survived to a following year, only about two-thirds of pairs reunited. Nearly half of the auklets paired in 1 year obtained a new mate in the following year, either because of mate disappearance or divorce. Interyear fidelity to mates was related only to male ornamentation; males with larger facial plumes were more likely to reunite with their mates the next year than males with smaller plumes. There were no significant differences in the ornaments of females in reunited and divorced pairs. Pairs that reunited also had significantly lighter plumage than pairs that divorced, and the plumage of males reuniting with their mates was significantly paler than that of divorced males. We conclude that the probability of both divorce and remating in this species is influenced by ornamental traits. Our finding that remating was related to male plumage color and ornaments is consistent with the idea that remating is influenced by female choice. Pairs that reunited also bred earlier in the season and had higher reproductive success than pairs with experienced individuals breeding together for the first time. We also found evidence that failure to breed in a given year increased the probability of subsequent divorce.
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An examination of feather replacement and plumage wear in study skins of Aimophila cassinii and A. aestivalis showed a sequence of molts and plumages for both as follows: Juvenal body plumage is replaced soon after fledging by a partial molt that produces plumage of adult-like body feathers combined with juvenal remiges, rectrices and greater primary and secondary coverts. This plumage has a spotted breast pattern intermediate between the streaked juvenal and spotless adult patterns, and is completely replaced in the bird's first autumn by a molt of all body, wing and tail feathers. A prolonged body molt of low intensity lasts through the spring-autumn breeding season, replacing feathers in all areas of the body. During autumn, adults have a complete molt coinciding with the second molt of the young birds. The replacement of all pennaceous body plumage twice within a bird's first six months of age, and a molt of body feathers in adults throughout the breeding season have not been reported before for a North American passerine, nor was this pattern described in an earlier study of the molt of these species. It is suggested that these partial molts renew plumage that otherwise would become severely worn in the birds' abrasive habitats.
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In birds, both males and females can exhibit socially selected traits, but relatively few studies address the role of female ornaments despite their potential importance in competitive female–female interactions and male mate choice. We investigated the melanized plumage pattern of male and female Spotted Sandpipers (Actitis macularius), a species with sex-role reversal and a polyandrous mating system. While the sexes overlap in the spottiness metrics, females had fewer, but larger and more irregularly shaped spots that covered a greater percentage of their plumage than did males. Feather mite load best explained the first principal component of plumage pattern (i.e. spot size) in females as well as in males. Sandpipers with lower mite loads had larger spots, but this relationship was less strong in males. Considering the second principal component (i.e. spot shape and percent cover), mass, hematocrit levels, and day captured best explained variation across females. Heavier females with higher hematocrit levels were caught later in the season and had more irregular spots and a higher percentage of melanized plumage cover. Spot pattern in recaptured individuals changed with capture year, indicating that spottiness varies within an individual's life. Overall, these results show that although the differences between the sexes are subtle, spottiness in Spotted Sandpipers is a measurably sexually dimorphic trait with females as the more ornamented sex, and that melanized ornaments can be indicators of female, and possibly male, condition.
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Cuckoo
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Psittaciformes
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Abstract Male signals may express the capacity to sustain environmental challenges. In some migratory birds like the Pied Flycatcher Ficedula hypoleuca , plumage ornaments are molted in the winter quarters shortly before spring migration while most feathers are replaced shortly after the breeding season in the breeding areas. The concentration of corticosterone in feathers (CORTf) may relate to baseline CORT levels at the time of molt which could be expressed through plumage signals. Male Pied Flycatchers present white patches on forehead feathers and tertials which are molted before spring migration and on secondaries and primaries replaced after breeding. They also express a variable degree of melanisation of head and back feathers molted in the wintering areas. All these plumage traits have been previously shown to function in social contests and/or mate attraction. Here we have collected tertials on the two wings and two tail feathers, molted in wintering and breeding areas respectively, of males in a Spanish montane population and analysed CORTf in the laboratory with standard enzyme immunoassays. There is no correlation within individuals between CORTf in the two types of feathers, although levels are similar. The size of the forehead patch is negatively associated with CORTf in tail feathers, mainly in small males, while the blackness of head and back is negatively related to CORTf in tertials, mainly in large males. The size of the wing patch composed of patches on feathers molted both in wintering (tertials) and breeding areas (primaries and secondaries) is not related to CORTf in any type of feather. Different male plumage traits thus may reflect circulating CORT levels during molt processes occurring in the wintering respectively breeding range as expressed by CORTf in different types of feathers.
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Abstract Immaculateness, a novel measure of bird plumage quality, defined as the regularity of the borders of a coloured patch of feathers, and the uniformity of the colour within the patch, tends to decline as a result of feather wear and damage. If it declines more quickly amongst birds in poor condition, it has the potential to act as an honest signal of individual quality and therefore be subject to social and sexual selection. We scored plumage immaculateness in shelducks Tadorna tadorna , based on the absence of white feathers in the red‐brown chest band and the evenness of the band's border. We monitored body condition and plumage quality in birds at feeding sites in the Severn Estuary (UK) during the early breeding season when females were forming eggs, and later in the season when chicks arrived. Drakes had more immaculate chest bands than ducks. At preferred feeding sites, drakes were more immaculate, and birds of both sexes were in better body condition. Birds with more immaculate plumage tended to mate assortatively at preferred sites and were more likely to produce a brood that survived the journey to the feeding areas. Immaculateness could therefore be an honest signal of parental quality. Although our evidence is only correlational, we suggest that plumage immaculateness indicates the ability to establish and maintain control over the best breeding sites and feeding territories in the face of competition with other shelducks.
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Summary Laycock, H. T. 1982. Moulting and plumage changes in the Thickbilled Weaver. Ostrich 53:91-101. Thickoilled Weavers were studied in captivity, in the wild and as museum specimens. Moulting follows the normal passerine pattern, but a difference from related species is that there is no post-fledging moult of the flight feathers. Methods were devised for identifying isolated feathers and for aging trapped birds, this being easier in the male. After the breeding season the male undergoes eclipse, which has apparently not been described before, and loses his white forehead patches. Adult males and females moult about the same time, but second-year males moult six or eight weeks earlier. The duration of post-nuptial moult is about four months and is timed to occur during the season when there is maximum food availability. The use of a “moult score” is avoided in this account and the timing of feather loss substituted as having more real meaning.
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Fledge
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Molting is an important process in which old and worn feathers are exchanged for new ones. Plumage color is determined by pigments such as carotenes, melanin and by the ultrastructure of the feather. The importance of plumage coloration has been widely studied in different groups of birds, generally at a particular time of the year. However, plumage coloration is not static and few studies have addressed the change in plumage color over time and its relationship to reproductive tasks. The Eared Dove (Zenaida auriculata, Des Murs, 1847) has a melanistic coloration with sexual dichromatism in different body regions. The Eared Dove´s crown is the most exposed body region during the bowing display. Our objective was therefore to accurately determine the molting period of the crown feathers and study the seasonal variation in their coloration in females and males. Our findings indicate a molting period of 6 months (January to June). The new feathers are undergoing changes in their coloration from July to December. During that period we apply an avian vision model then enabled us to reveal a seasonal variation in the coloration of the crown feathers in both sexes, as given by a change in the chromatic distances. The highest values in the chromatic distances towards the reproductive period are given by a change in the UV-violet component of the spectrum, indicating changes in the microstructure of the feather. This change in crown coloration towards the breeding season could be linked to reproductive behaviors.
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Streptopelia
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