Plumage Variation Research Articles

Epaulet Brightness and Condition in Female Red-Winged Blackbirds

Epaulets of female Red-winged Blackbirds (Agelaius phoeniceus) vary in bright- ness from brown to bright red-orange. We test predictions of the hypothesis that condition at the time of molt determines female epaulet brightness and that females in superior con- dition produce brighter epaulets. We compared each female's epaulet with a series of color photographs ranked from 1 (dull brown) to 12 (bright red-orange) and considered females to have increased in brightness between years if their color increased by at least two ranks. More first-year females than older females increased in brightness, more older females in- creased in brightness after low reproductive effort than after high effort, and more first-year females increased in brightness after a year of superabundant food (an emergence of periodical cicadas, Magicicada spp.) than after other years. In each case, we expected an improvement in condition. We estimated female condition and regressed condition index on day of the breeding season. During the breeding season, females that later increased in brightness improved in condition relative to females that did not increase in brightness. We confirm a previously reported correlation between age and epaulet brightness, but age does not explain the relationship between change in brightness and either reproductive effort or the emergence of cicadas. We conclude that the most likely explanation for our results is that condition, at least in part, determines epaulet brightness in female Red-winged Blackbirds and that superior condition is reflected by brighter epaulets. Our results support assumptions of the status- signaling hypothesis and mate-choice hypotheses for the evolution of variable plumage. The best explanation for the evolution of variable plumage among female Red-winged Blackbirds is that brightness signals status in female-female aggressive encounters. Received 21 November

Variation in Male Plumage and Behavior of the Hawaii Akepa

-The sexually dichromatic and endangered Island of Hawaii subspecies of Akepa (Loxops coccineus coccineus) is a 10to 12-g Hawaiian honeycreeper that shows remarkable variation in male plumage coloration, ranging from dull gray to bright orange. We found that this variation is primarily due to a two-year delay in plumage maturation by young males. Second-year males possess a mainly grayish-green plumage that is similar to that of females, and rarely try to breed. Third-year males have a partially orange plumage that is intermediate between that of females and adult males, and competently breed in small numbers. In addition, there are variations within age classes that reflect alternative life histories and perhaps diet. The existence of both femalelike and malelike subadult plumage in a population is unlike North American passerines with delayed plumage maturation, especially cardueline finches, which are considered to be the closest relatives of the Hawaiian honeycreepers. The extreme delay is associated with high survivorship, strong philopatry, and a varied prebreeding competition among males that includes group displays and which lasts for six months or more each year. These characteristics are common in lekking or cooperatively breeding species, but are unusual for a small, monogamous passerine with biparental care. Received 1 October 1993, accepted 11 January 1994. FEW PHENOTYPIC CHARACTERS SO closely track the life history and social system of birds as do color and brightness of plumage (Baker and Parker 1979, Rohwer and Butcher 1988, Butcher and Rohwer 1989). Plumage can make an individual more or less conspicuous to predators, ecological competitors, sexual rivals, and potential mates, and may reflect a genotype that has superior tolerance of or resistance to diseases and parasites (Hamilton and Zuk 1982). The relation between plumage and reproductive maturity also has been identified as an example of paedomorphosis or heterochrony in birds (Lawton and Lawton 1986). Whereas birds typically reach adult size within a year after fledging, individuals may become sexually mature before acquiring terminal adult plumage. Delayed maturation of plumage, appropriately identified as a neotenic character, has been documented in numerous avian orders and families and has been shown to be related to complexity of social organization (Lawton and Lawton 1986) and to intensity of sexual selection (Selander 1965, Rohwer et al. 1980, Studd and Robertson

Mitochondrial Analysis of Gene Flow between New Zealand Mallards (Anas platyrhynchos) and Grey Ducks (A. superciliosa)

ABSTP,CT.--One of the more well-known examples of hybridization in birds is the frequently documented occurrence between sexually dimorphic Mallards (Anas platyrhynchos) and several closely related nondimorphic species in the mallard complex. In New Zealand, the Grey Duck (Anas superciliosa superciliosa) is the indigenous, nondimorphic Mallardlike species, and extensive hybridization with introduced Mallards has been implicated in the population decline of Grey Ducks. Individuals from throughout the country were classified phenotypically as parentals or hybrids based on variation in plumage, bill color, and leg color. We confirmed species-specific mitochondrial DNA haplotypes by comparing restrictionenzyme fragment patterns in Grey Ducks and New Zealand Mallards to those of Pacific Black Ducks (A. superciliosa rogersi) from Australia and Mallards from North America, respectively. Our data indicate that hybridization has led not only to introgression of Grey Duck mtDNA into Mallard populations (the predicted direction of gene flow), but also to significant introgression of Mallard mtDNA into Grey Duck populations. Thus, the contention that hybridization between Mallards and nondimorphic species involves primarily Mallard males with females of the other species is not upheld for this example from New Zealand. The speciation process appears to be undergoing reversal. Received I April 1993, accepted 2 July 1993. THE INCIDENCE OF interspecific and intergeneric hybridization in the order Anseriformes is higher than in any other order of birds, reaching 30 to 40% by some estimates (Grant and Grant 1992). In addition, a substantial proportion of interspecific hybrids (20%) in this order have been reported to be fertile (Scherer and Hilsberg 1982), so there is potential for extensive gene flow and introgression between some species. Among the more well-known examples is the frequently documented incidence of hybridization between sexually dimorphic Mallards (Anas platyrhynchos) and several closely related, nondimorphic species. For instance, in North America, hybridization with Mallards has been implicated as one factor in the population decline of American Black Ducks (A. rubripes; Johnsgard 1967, Heusmann 1974, Ankney et al. 1987), Hawaiian Ducks (A. wyvilliana; Griffin et al. 1989), and Mexican Ducks (A. platyrhynchos diazi; Hubbard 1977). Increasing numbers of

Geographic variation in size and sexual dimorphism across a hybrid zone between Carrion Crows (Corvus corone corone) and Hooded Crows (C. c. cornix)

Sexual size dimorphism was analysed across a hybrid zone existing between allopatric populations of Carrion Crows and Hooded Crows (Corvus corone corone and C. c. cornix) in northwestern Italy. Twenty-five morphological (osteological and plumage) variables were measured in a sample of 1599 specimens obtained from allopatric parental areas and from the hybrid zone. For each morphological variable considered, sexual size dimorphism was measured as the ratio of males/females or the absolute difference between mean sizes of males and females within each subpopulation studied. Overall sexual size dimorphism was described by discriminant function analysis. All the sexual size dimorphism measures adopted showed variation across the hybrid zone according to elevation. Male/female ratios and male–female differences significantly differed between the parental allopatric "operational taxonomic units," Carrion Crows being more dimorphic than Hooded Crows. Across the hybrid zone, sexual size dimorphism was correlated with the phenotypic composition of the crow subpopulations and with size of males but not size of females. The data presented show that sexual size dimorphism is correlated with an ecological gradient and that its geographical variation is determined by variation in size of males only.

Plumage Variation, Plasma Steroids and Social Dominance in Male House Finches

In male House Finches (Carpodacus mexicanus), the extent and color of plumage varies depending on access to carotenoid pigments. Colorful males exhibit extensive red pigmentation, while less colorful (i.e., drab) males exhibit carotenoid pigmentation over a smaller percentage of their plumage, pigmentation of a color besides red (e.g., yellow, gold, orange, or pink), or both. One explanation for maintenance of plumage variation is that it reliably reflects social status, allowing males to correctly assess their status in relation to others and avoid or minimize costly fights. Social relationships may also be related to endogenous factors, such as circulating levels of the hormones testosterone and corticosterone. High levels of testosterone may promote or facilitate increased aggression, and stress associated with receiving aggression from individuals of higher status may increase adrenal activity and secretion of corticosterone. We examined the relationship between plumage variability, steroid hormones, and social status in captive male House Finches during the non-breeding period in: (1) groups of males in which individuals varied by age, size, and plumage, and (2) pairs (dyads) of males matched for several measurable parameters except plumage. Testosterone and social status were not related in males competing in either groups or dyads, and levels of testosterone were routinely low. Corticosterone and status were not related in groups but, in dyads where subordinate individuals had little chance of escaping aggression from more dominant birds, subordinates exhibited significantly greater levels of corticosterone. Although drab males tended to achieve higher status than colorful males in both experiments, which is consistent with previous studies on free-living individuals, we could not reject the null hypothesis that plumage and status were unrelated. We conclude that dominance relationships among male House Finches during the non-breeding season may not be related to testosterone, but they are reflected by levels of corticosterone in some circumstances. Additionally, colorful plumage appears to be a poor predictor of high social status among male House Finches during the non-breeding season.

Extraordinary Sex Roles in the Eurasian Dotterel: Female Mating Arenas, Female-Female Competition, and Female Mate Choice

The mating system of the Eurasian dotterel, Charadrius morinellus, is compared with what would be expected in sex-role-reversed lekking (i.e., female-female competition and mate choice by males). Female dotterel are potentially polyandrous and, in this study, compete for access to males on mating arenas. Males provide all parental care. Intrasexual plumage variation is prominent in both sexes. Bright females win more of their fights than do dull females because bright females are more likely to initiate fights, and all females are unlikely to attack females brighter than themselves. Also, compared with dull females, bright females do more courting, pair earlier in the season, and are more likely to pair with a bright male. Since bright males are apparently in better physical condition than dull males, we suggest that females prefer males that will be good parents. Thus, as no evidence was found of any active mate choice by males, it seems that females are the more active sex in mate choice. Hence, although competition among females on the mating arenas of the dotterel resembles competition among males on leks, the direction of mate choice does not appear to match the analogy of sex-role-reversed lekking. This observation suggests that competition and mate choice are not simply opposite sex roles-individuals of one sex can both compete for mates and exert mate choice.

Color Variation and Hybridization among Nesospiza Buntings on Inaccessible Island, Tristan da Cunha

Nesospiza buntings have speciated at the Tristan da Cunha archipelago in the central South Atlantic Ocean. Two species, the Tristan Bunting (N. acunhae) and Wilkins' Bunting (N. wilkinsi), differ markedly in size and co-occur without interbreeding on Night- ingale Island. Nearby Inaccessible Island supports two altitudinally segregated color morphs of N. acunhae, as well as a hybrid complex involving acunhae and wilkinsi. Plumage variation was evaluated for 581 buntings, most of which were caught on Inaccessible Island. Nesospiza plumages vary with age and sex; immature plumage is retained for at least two years. Despite age and sex differences, there is no overlap in coloration between the upland and lowland morphs of N. acunhae on Inaccessible Island. The two morphs are distinct from the time of hatching; chicks of lowland acunhae are pinkish, whereas upland acunhae are yellow. Color differences between acunhae morphs were quantitative rather than qualitative; their feathers contain the same suite of carotenoid pigments, but at three times greater concentration in upland birds. Dispersion of different bunting populations on Inaccessible Island is closely related to vegetation types. Individually marked individuals were largely sedentary; only immature birds moved more than 400 m. The parapatric dispersion of acunhae morphs prob- ably results from habitat-specific dietary differences. Nertera fruits are likely sources of ca- rotenoid pigments in the diets of buntings, but feeding experiments on captive birds are needed to elucidate fully the basis of color variation between morphs. Whatever the proximate cause, plumage-color variation may allow population differentiation if birds mate assortatively on the basis of color. A review of previous visits to the islands suggests that the diversity of

Geographic Variation in Morphology and Allozymes of South American Imperial Shags

To evaluate the hypothesis that Pleistocene glaciations in southern South America effected differentiation in the Imperial Shag (Phalacrocorax atriceps), I analyzed geographic variation in plumage, skeletal size and proportions, and allozymes in populations from seven South American localities. Alar bar size, crest length, and the size of the white dorsal patch vary geographically among juveniles but not adults, and the alar bar and white dorsal patch are both present all year in adults. Geographic variation in osteology is marked, with males showing more interpopulational differentiation than females. Coastal populations follow Bergmann's rule, while freshwater Fuegian lake shags are smaller than coastal populations even though the geographically nearest coastal population is the largest one in body size. Shags from the lowest latitude, in central Chile, have relatively long culmens, conforming to Allen's rule. All populations except that from Chubut Province are very similar in allozyme frequencies, and the very low genetic distances between populations are noncongruent with the greater degree of morphological differentiation, particularly between lake and coastal populations. The genetically differentiated Chubut population was probably somewhat isolated on the Patagonian Massif, a circumstance unrelated to Pleistocene glaciations. Chilean shags were probably not long reduced during glaciations to a small isolate, because they can form colonies on unglaciated headlands; they are only slightly differentiated from Atlantic populations. The treatment of the Falkland Islands population as a distinct subspecies is supported by plumage characters. The freshwater Fuegian shags must have differentiated since glacial recession. The populations from the southern Atlantic coast and coastal Tierra del Fuego, which were probably contiguous throughout the Pleistocene, differ from each other only clinally in size. Unlike the cases of other Fuego-Patagonian species studied, Pleistocene vicariance events appear to have had little influence on the evolutionary history of the Imperial Shag. This is probably related to life-history traits of this species such as coloniality, vagility, longevity, trophic generalism, and cold tolerance.

Social status signalling in white-crowned sparrows: an experimental test of the social control hypothesis

Abstract. Some winter flocking passerines possess variable plumage that functions to signal social status. The social control hypothesis has been proposed to explain why subordinate birds do not cheat by displaying the brighter signal of dominant birds. This hypothesis assumes like-versus-like aggression between dominants and suggests that cheating is prevented by an increase in the number of interactions that cheaters encounter with legitimately dominant birds. The presence of like-versus-like aggression in white-crowned sparrows, Zonotrichia leucophrys, was assessed by simultaneously introducing an adult and immature male, members of the highest and next to lowest ranking age-sex classes, respectively, into four aviaries containing resident adult and immature males. Contrary to the social control hypothesis there was no difference in the amount of aggression resident adults directed against introduced adults and immatures. Furthermore, resident adult males did not initiate aggression against other resident adult males more often than against resident immature males. Adult residents behaved the same regardless of whether they were the more or less common age class among residents. Social control is unlikely to be responsible for the evolutionary stability of social status signalling in white-crowned sparrows, and a review of other studies reveals little evidence that it controls cheating in any species.

Variation in Black Bib of the Eurasian Siskin (Carduelis spinus) and Its Role as a Reliable Badge of Dominance

Rohwer (1975, 1982) proposed that the variation and extent of color patches in the plumage of wintering birds could work as badges of social status. The major advantage of these signals would be that individuals of unequal status competing for limited resources would not need to risk accidental injury or waste energy assessing the relative fighting ability of potential opponents (Rohwer 1982). The status-signalling hypothesis has been tested in several species with variable plumage (reviewed by Whitfield 1987; see also Amat 1986, Watt 1986a, b, Fugle and Rothstein 1987, Moller 1987a, b,1989, Jackson et al. 1988). These studies have, however, produced contradictory results. For plumage differences to act as true badges of dominance, they should correlate within and not just between sex and age classes. This has been demonstrated in only a few species (Great Tit [Parus major], Jarvi and Bakken 1984; Yellow Warbler [Dendroica petechia], Studd and Robertson 1985; House Sparrow [Passer domesticus], Meller 1987a; Whitfield 1987; see however Ritchison 1985, Poysa 1988, Wilson 1992). The Eurasian Siskin (Carduelis spinus) shows great variability in the extent of blackish plumage in the bib (Newton 1972). This chin patch, as in House Sparrows (Moller 1987a), is present only in males, which are dominant over females. Dominance, however, is unaffected by age (Senar 1985). This lack of a relationship between age and dominance, and the absence of the badge in females simplifies analysis of the significance of the chin patch in status signalling. Other features in the Eurasian Siskin plumage also could be used for dominance signalling. For instance, yellow wing stripes have been found to work as a badge of status in its American counterpart, the Pine Siskin (Carduelis pinus; Balph and Balph unpubl. paper); they could have an important role. However, since wings are displayed in only 25% of the agonistic displays used by the Eurasian Siskin (Senar 1990), the chin is always visible, and most of the encounters between unfamiliar birds in wild flocks are between males (i.e. the badged individuals; Senar et al. 1990b), we restricted this analysis to the black bib. We describe variation in the size of the chin patch in male Eurasian Siskins and test (both in captivity and in the field) whether this variation is related to dominance status. Methods.-Plumage variability and dominance relations in the field were studied in a suburban area of Barcelona (NE Spain) during the 1990-1991 winter. Birds were trapped at baited feeders using platform traps and clap nets, and were marked with numbered aluminium bands. Trapping was carried out at least twice weekly, but the food was available continually so that Eurasian Siskins used the area heavily. For each male siskin we recorded, whenever possible, age and the maximum length and breadth of the badge. Badge size was measured by tilting the bird's head back in line with the body. Following the procedure of Moller (1987a), we determined the relationship between badge area, length (L, mm) and breadth (B, mm) from 12 museum skins. Thus, badge area (A, mm) was calculated as:

Plumage Variability in Redpolls from Churchill, Manitoba

-Redpolls (Carduelis flammea and C. hornemanni) are well known for their extensive phenotypic variability. Various explanations have been proposed for the phenomenon, ranging from extreme variability within a single inclusive taxon, to more modest variation within frequently hybridizing or strictly isolated taxa. The predominant view favors the recognition of two largely sympatric and only slightly differentiated species: the Common Redpoll (C. flammea), comprised of the four subspecies flammea, cabaret, islandica, and rostrata; and the Hoary Redpoll (C. hornemanni) comprised of the two subspecies hornemanni and exilipes. We investigated the possible existence of sympatric redpoll forms in a large sample (n = 209) of breeding individuals from Churchill, Manitoba, where the putative forms flammea and exilipes were reported to co-occur. Groups of individuals of specific age and sex were analyzed independently. The sample was not divided a priori into flammea and exilipes subgroups. The pattern of variation within each age-and-sex group is described, and the differences between these groups are analyzed. We show that several pigmentation characters in specific age-andsex groups are not distributed normally, and that pale and dark subgroups of second-year (SY) and after-second-year (ASY) males can be identified in a principal-components analysis (PCA) of seven characters reflecting the extent of melanin and carotenoid pigmentation. The pinkand red-breasted subgroups of ASY males match almost perfectly the pale and dark groups found in the PCA analysis. Further, when ASY males of different breast color (pink vs. red) are analyzed independently, all plumage characters are distributed normally. The analyses of SY and ASY females failed to provide good evidence for a plumage polymorphism. Our results support the idea that two relatively distinct redpoll forms breed at Churchill, which differ in several plumage characteristics involving both melanin and carotenoid pigmentations. These forms are more clearly differentiated in males than in females. They may be specifically distinct (C. f. flammea and C. hornemanni exilipes), as has frequently been suggested, but they also could be the product of different types of intraspecific genetic or ecophenotypic polymorphisms. Preliminary observations are presented that support the idea that plumage variants are largely genetically determined, but experimental work is needed to confirm this suggestion. Received 28 May 1991, accepted 19 February 1992. ORNITHOLOGISTS HAVE long been intrigued by the extensive plumage variability seen in redpolls (Carduelis [flammea] spp.). Based roughly on the same type of data and analytical approach (i.e. colorimetric and morphometric studies), different investigators have described that variation as continuous (e.g. Harris et al. 1965, Troy 1985) or dimorphic (e.g. Todd 1963, Molau 1985, Knox 1988), and have divided the complex into one to four species (see Knox 1988:table 1). The taxonomic disagreement comes mainly from the different interpretations given to the origin of birds having intermediate attributes in sympatric populations. Some re1 Present addresses: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA; and Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002, USA. searchers hold that intermediate birds are common in many populations and represent either hybrids and backcross individuals (e.g. Williamson 1961, Harris et al. 1965), or merely central points in a homogeneous distribution of phenotypic variants within a single highly variable species (Troy 1985). Other investigators (e.g. Molau 1985, Knox 1988) have suggested that, when sexual and age dimorphisms are carefully taken into account, very few redpolls qualify as intermediate, and these probably are convergent variants of distinct sympatric species. The most commonly encountered classification of redpolls is one in which two polytypic species are recognized, the Common Redpoll (C. flammea) comprised of the subspecies cabaret, flammea, and rostrata, and the Hoary Redpoll (C. hornemanni) comprised of the subspecies exilipes and hornemanni (Knox 1988). The taxonomic affinities of redpolls breeding in Iceland are un-

Widespread polychromatism in female sunangel hummingbirds (Heliangelus: Trochilidae)

In hummingbirds, a showy gorget of iridescent throat feathers is a characteristic male ornament in many sexually dichromatic species. Given that polygynous breeding systems are the only ones observed in hummingbirds, and that polygyny is often associated with dramatic male ornamentation and sexual dimorphism, it is not surprising that gorgets are usually interpreted as sexual display characters. This proposition is challenged by exceptional ‘polychromatic’ species in which adult females diner in their development of a male-like gorget. This analysis focuses on determining the prevalence of polychromatic variation in the Andean genus Heliangelus. In eight of nine species, females' gorgets range from a dull plumage characteristic of most female hummingbirds (female-like), to a bright iridescent plumage that matches that of the males (male-like). Analysis of museum study-skins reveals that individual variation in gorget colour is limited to females, and that it is independent of month and year of collection. Only H. exortis and H. amethysticollis exhibit significant geographic variation in the frequencies of different colour forms, though most male-like female H. amethysticollis occur in southern Ecuador-northern Peru. Some species-specific features of the male-like females' gorget appear to be linked to qualities of the male gorget (presence/absence, colour and maximum size). However, non-adaptive hypotheses, including genetic correlation between the sexes, hybridization and neutral variation, cannot account for the plumage variation among females. The absence of any association between female gorget colour and breeding condition suggests that gorget colour has a non-sexual function. I propose that gorgets can evolve solely as a non-sexual signal associated with different foraging behaviours.

Plumage and Size Variation in the Mourning Warbler

Plumage and Size Variation in the Mourning Warbler

Plumage variation and dominance in captive female Red-winged Blackbirds

Flocks of female Red-winged Blackbirds (Agelaius phoeniceus) were maintained in aviaries to determine whether variation in brightness of epaulette or chin plumage correlated with dominance status in nonbreeding situations. No correlation was found between natural plumage variation and dominance in eight control groups, although dominant females were heavier and in better condition. In two groups in which epaulettes were experimentally brightened on some birds and two groups where some chins were brightened, brightening an individual's plumage had no consistent effect on dominance status. Thus, we did not find any evidence that there is direct selection on female plumage brightness for signalling competitive ability outside the breeding season. We propose that bright plumage in females could be an indirect consequence of genetic correlation with a trait selected for in males.

Plumage variability functions for status signalling in least auklets

This study investigated whether the variable plumage of the least auklet, Aethia pusilla, a small seabird of the Bering Sea, functions for status signalling. Adult least auklets varied continuously in underpart colour from unmarked white to nearly black. Although there was variability within age groups, adults tended to lighten in plumage as they aged. There were no differences in plumage between the sexes. Observations of natural interactions among adult and immature birds of different plumage indicated that lighter birds usually defeated darker birds in agonistic interactions within each age group. Model presentation experiments were performed to test whether plumage colour alone signals social status. Auklet models presented in white plumage were approached less closely and induced more responding adult and immature birds to flee compared to the same models presented with dark plumage. Furthermore, birds with lighter plumage approached the white model closer than did birds with darker plumage. The results provide evidence for status signalling by plumage in a non-passerine bird and document another species where status signalling works within age (adult versus immature) categories.

Habitat Segregation by Sex in the Hooded Warbler: Experiments on Proximate Causation and Discussion of Its Evolution

Although habitat choice has been shown to have an innate basis in some vertebrates, few experimental studies have been performed, and these most often relied on interspecific comparisons. Male and female hooded warblers (Wilsonia citrina) defend territories in markedly different habitats while wintering in the tropics. Males use forests; females use shrub or field habitats. I used naive handraised warblers in experiments designed to test for sex-related innate differences in habitat selection. Choosing between two three-dimensional artificial habitats, males chose the tall habitat with separated stems over the short habitat with dense stems, whereas females showed no preference. Field observations and a laboratory experiment with the naive birds showed no habitat preferences based on light intensity. Finally, naive warblers were exposed to a two-dimensional array of black stripes on opposite walls of an experimental room, one wall with the black stripes arranged vertically and the other with the stripes arranged at oblique angles to the floor. Males oriented toward the vertical stripes, whereas females oriented toward the oblique stripes. Since forests have more vertical structures than shrubby fields, an innate preference for cues based on vertical or oblique cues is a sufficient proximate mechanism to bring about the observed habitat segregation between the sexes in wild birds. I discuss possible sources of selection favoring the evolution of intraspecific habitat segregation by sex. A hypothesis is presented to explain the presence of a subadult female plumage and a highly variable adult female plumage as they relate to habitat segregation in the hooded warbler. I suggest that this unusual plumage variability in females resulted from changes in the habitat available to females after swidden agriculture began in their main wintering area.

Breeding biology and current status of the Amsterdam Island Albatross Diomedea amsterdamensis

A small population of the ‘Great Albatrosses’ has been discovered on Amsterdam Island (Indian Ocean) and described in 1983 as a new species: Diomedea amsterdamensis (Roux et al. 1983). We present here data on the biometry, plumage variability and preliminary results of a long‐term study on the breeding cycle and population dynamics of this relict population. The current population is estimated at 65 birds including 21 breeding pairs.

Unusual Variations in Plumage of House Sparrow

Unusual Variations in Plumage of House Sparrow

Influence of age and territory quality on the reproductive behaviour of male Yellow Warblers

Individual male Yellow Warblers (Dendroica petechia) exhibit differences in their level of parental investment, which correlate with the amount of brown streaking on the breast. We tested two alternative hypotheses to explain these patterns. The age effect hypothesis proposes that the variation in plumage and parental behaviour is an effect of differences in male age. This was tested by analyzing the nest visit rates and plumage scores of banded males present in the study in more than 1 year. The age effect hypothesis is rejected because there was no evidence of significant within-male variation due to increasing age, nor of any consistent directional change in either parental effort or plumage pattern between years. The territory quality hypothesis proposes that the quality of territory occupied has an important proximate influence on male parental effort. By observing the same territories over different years we were able to compare nest visit rates of different males with different plumage scores while holding the effect of territory quality constant. Analysis of variance revealed that male plumage rank had a highly significant effect on nest visit rate, while the effect of territory occupied was not significant. Rejection of these two alternative hypotheses provides further support for the hypothesis that phenotypically different males are using alternative and irreversible lifetime reproductive strategies.

Plumage Pigment Differences in Manakins of the Pipra Erythrocephala Superspecies

-We investigated the carotenoids found in the head feathers of three members of the Pipra erythrocephala superspecies by chromatographic, spectrophotometric, and chemical means. The Golden-headed Manakin (P. erythrocephala) primarily deposited yellow hydroxycarotenoids in its head feathers, predominately lutein. Red keto-carotenoids were also deposited locally. Canthaxanthin, for instance, was identified in the tips of nape feathers. In contrast, the Red-headed Manakin (P. rubrocapilla) deposited mostly orange and red ketocarotenoids. An orange pigment identified as a-doradexanthin was the most abundant. The common red pigments astaxanthin and canthaxanthin were also present. Finally, feathers of the red-headed Round-tailed Manakin (P. chloromeros) yielded a complement of carotenoids very similar to the Red-headed Manakin's. In addition, the Round-tailed Manakin deposited moderate amounts of rhodoxanthin, a plant keto-carotenoid of pronounced red hue. Within individual Red-headed Manakins, we observed differences in total carotenoid content and composition among head regions that differed slightly in color. The distal and proximal portions of individual feathers also differed markedly. We discuss possible physiological and biochemical mechanisms for these conditions, and suggest their relationship to the mechanisms responsible for the species-specific differences in manakin coloration. We reveal the probable origin of the Latin misnomer for the Golden-headed Manakin. Received 2 August 1988, accepted 2 August 1988. THE four species of Neotropical manakins that compose the Pipra erythrocephala superspecies (Snow 1979) differ conspicuously in the combination of their head, thigh, and underwing colors (Table 1). The difference in head color is particularly striking between the Golden-headed Manakin (Pipra erythrocephala) and its close relatives. The golden top and sides of the head of P. erythrocephala, belying its scientific name, contrast sharply with the bright red head of the other three allospecies. The colors involved are generally bright, and presumably implicate carotenoid pigments (Brush 1981). However, the biochemical and genetic basis of the color differences remains unexplored. P. erythrocephala is closely related to the Redheaded Manakin (P. rubrocapilla), with which it has been grouped in a single species (P. e. erythrocephala and P. e. rubrocapilla of Hellmayr 1929). The distribution of P. erythrocephala and P. rubrocapilla at their area of closest contact is delimited largely by the Amazon River. The 3To whom all reprint requests should be sent. occurrence of morphological differentiation associated with rivers is often found among understory Amazonian forest birds, a pattern largely unique to Amazonia (e.g. Hellmayr 1910, Snethlage 1913). One interpretation is that rivers act as barriers to gene flow and serve as geographical isolating mechanisms (Sick 1967). Capparella (1987, in press) reported large genetic distances between the two manakins, in excess of the mean for avian species [Nei's (1978) D = 0.101; avian mean 0.0440 ? 0.0221 SD, Barrowclough 1980] based on allozyme studies. Moreover, fixed differences were detected at three loci, a condition often lacking between undisputed avian species. Carotenoid pigments, responsible for most of the bright colors in birds, are relatively wellknown chemically. Furthermore, considerable work has been concerned with their biochemical modification and processing in birds (reviewed in Brush 1981). Differences in feather carotenoids are determined by both the processes responsible for their absorption and transport, and the metabolic capacities of the 34 The Auk 106: 34-41. January 1989 This content downloaded from 157.55.39.135 on Sun, 03 Jul 2016 06:06:41 UTC All use subject to http://about.jstor.org/terms January 1989] Pigment Differences in Pipra 35 birds to modify the pigments. Hence, carotenoid analysis can be used to infer physiological, and the underlying genetic, differences. In addition to providing specific plumage color and patterns (Fox and Hopkins 1966, Fox et al. 1967, Brush 1970, Brush and Johnson 1976, Troy and Brush 1983), carotenoid differences account for color polymorphisms (Volker 1964, Brush and Seifried 1968, Johnson and Brush 1972), subspecific plumage variation (Test 1942, Ford and Simpson 1987), and plumage variants (Volker 1964, Brush 1970, Hudon and Brush in press). To elucidate the nature of the physiological differences that confer species specificity of coloration in the manakins, we determined the pigment constitutions responsible for the difference in head color between P. erythrocephala and P. rubrocapilla. The Round-tailed Manakin (P. chloromeros), another member of the P. erythrocephala superspecies, was also ex-