Published by: The American Ornithologists' Union
July 2016 : Volume 133 Issue 3
A quantitative analysis of objective feather color assessment: Measurements in the laboratory do not reflect true plumage color
Iker Vaquero-Alba, Andrew McGowan, Daniel Pincheira-Donoso, Matthew R. Evans and Sasha R. X. Dall
An important driver of the evolution of animal coloration is sexual selection operating on traits that are used to transmit information to rivals and potential mates, which has a major impact on fitness. Reflectance spectrometry has become a standard color-measuring tool, especially after the discovery of tetrachromacy in birds and their ability to detect UV light. Birds' plumage patterns may be invisible to humans, and therefore the establishment of reliable and quantitatively objective ways of assessing coloration not dependent on human vision is a technical need of primary importance. Plumage coloration measurements can be taken directly on live birds in the field, or in the laboratory (e.g., on collected feathers). However, which of these 2 approaches offers a more reliable, repeatable sampling method remains an unsolved question. Using a spectrophotometer, we measured melanin-based coloration in the plumage of Barn Swallows (Hirundo rustica). We assessed the repeatability of measures obtained with both traditional sampling methods to quantitatively determine their reliability. We used an ANOVA-based method for calculating the repeatability of measurements from 2 years separately, and a GLMM-based method to calculate overall adjusted repeatabilities for both years. The results of our study indicate a great disparity between color measurements obtained using both sampling methods and a low comparability across them. Assuming that measurements taken in the field reflect the real or “true” color of plumage, we may conclude that there is a lack of reliability of the laboratory method to reflect this true color in melanin-based plumages. Likewise, we recommend the use of the GLMM-based statistical method for repeatability calculations, as it allows the inclusion of random factors and the calculation of more realistic, adjusted repeatabilities. It also reduces the number of necessary tests, thereby increasing power, and it allows easy calculation of 95% CIs, a measure of the reliability and precision of effect-size calculations.
Male Red-backed Fairywrens appear to enhance a plumage-based signal via adventitious molt
Samantha M. Lantz and Jordan Karubian
Phenotypically plastic signals that can be altered in response to changing environmental conditions provide animals with the ability to dynamically signal their current condition or status. Such flexibility might also provide a means of avoiding potential trade-offs between signal components. Among birds, for example, both the timing of expression and the coloration of nuptial plumage are often thought to be honest signals of condition. However, because plumage is a relatively static signal type, birds that express condition-dependent plumage signals may face a trade-off between timing of signal production and signal quality, in that signals produced relatively early may be of lower quality because of seasonal constraints. A related cost may be increased fading or wear of plumage associated with extended duration of signal expression. Male Red-backed Fairywrens (Malurus melanocephalus) exhibit asynchronous development of nuptial red–black plumage, with some individuals molting into nuptial plumage months earlier than others. We report that male Red-backed Fairywrens that molt into nuptial red–black plumage early during the nonbreeding season appear to increase their plumage coloration by replacing feathers outside of normal molt periods (i.e. adventitious molt). In this way, some male Red-backed Fairywrens may be able to molt into nuptial plumage in the nonbreeding season, which is likely to increase access to mates or resources, and to subsequently enhance the red hue of a plumage-based sexual signal to a putatively more attractive state. We suggest that adventitious molt may be a currently underappreciated mechanism that birds use to improve or maintain the quality of plumage-based signals over time, between periodic full-body molts.
Reproductive biology of the Sapayoa (Sapayoa aenigma), the “Old World suboscine” of the New World
Sarah A. Dzielski, Benjamin M. Van Doren, Jack P. Hruska and Justin M. Hite
The Sapayoa (Sapayoa aenigma), a low-density resident of Chocó rainforests from Panama to Ecuador, has long perplexed ornithologists. It was originally described as a manakin (Pipridae), but molecular work has revealed its closest living relatives to be Old World suboscines (Eurylaimides) and supported its placement in the monotypic family of Sapayoidae. Despite such phylogenetic intrigue, little is known about the Sapayoa's general life history or reproductive biology; only one nest has been described. We present information on 2 actively attended and 13 inactive Sapayoa nests in Darién National Park, Panama. We provide the first detailed description of individual effort at an active nest, family group dynamics during the nesting period, the plumage of immature birds, and the range of vocalizations produced. We also present the first documentation of cooperative breeding and compile several recent nesting observations, extending the published Sapayoa breeding period by several months. Furthermore, we describe unusual behaviors among provisioning birds, including mounting between individuals of the same sex and mounting of a female by immature male helpers during chick provisioning. The receiving individual gave a conspicuous solicitation display before each mounting. Finally, we highlight elements of the Sapayoa's natural history that echo its Old World relatives and contrast with members of the New World Tyranni. For example, the Sapayoa resembles the eurylaimid broadbills—and differs starkly from the manakins—in diet, nest structure, breeding system, and mode of parental care.
Habitat and social factors influence nest-site selection in Arctic-breeding shorebirds
Jenny A. Cunningham, Dylan C. Kesler and Richard B. Lanctot
Habitat selection theory suggests that shorebirds should choose nest sites that maximize survival and fitness. We investigated how habitat, and proximity to conspecific or heterospecific nesting birds, was related to nest-site selection in American Golden-Plovers (Pluvialis dominica), Dunlin (Calidris alpina), Long-billed Dowitchers (Limnodromus scolopaceus), Pectoral Sandpipers (C. melanotos), Red Phalaropes (Phalaropus fulicarius), and Semipalmated Sandpipers (C. pusilla) in Barrow, Alaska, USA, between 2005 and 2012. We used remote-sensing data to link habitat information to used and unused nest sites, and we measured distances from nests to other nearby nesting shorebird neighbors. Results from an information-theoretic approach to identify best-approximating models indicated that all species selected nest sites on the basis of both habitat and social cues. Macroscale tundra moisture level within 50 m of the nest, which was closely associated with vegetation community, was an informative variable for Dunlin, Long-billed Dowitcher, and Red Phalarope, which all selected wetter habitat. Enhanced tundra microrelief increased the probability of nest-site selection for American Golden-Plover, Long-billed Dowitcher, Pectoral Sandpiper, and Semipalmated Sandpiper. American Golden-Plover, Dunlin, Pectoral Sandpiper, and Semipalmated Sandpiper selected sites farther from conspecific nests than predicted by chance. Our results indicate that shorebirds select nest sites on the basis of habitat features, and that some are also influenced by proximity to other nesting shorebirds. These findings indicate that shorebirds select nests that are likely to aid incubation abilities, reduce predator detection of nesting birds, enhance detection of predators, enhance foraging, and reduce competition from conspecifics. The variable needs of the different Arctic-breeding shorebirds indicate that climate change will have both beneficial and harmful consequences. Our habitat models may be useful for predicting areas of high shorebird importance throughout the Arctic Coastal Plain, allowing mitigation of proposed anthropogenic developments.
Effects of tidal periodicities and diurnal foraging constraints on the density of foraging wading birds
Leonardo Calle, Dale E. Gawlik, Zhixiao Xie, Lauri Green, Brian Lapointe and Allan Strong
In intertidal zones, tidal cycles reduce water depths and provide areas of shallow water where wading birds can forage for aquatic prey (water depths 0–50 cm). However, a bird that forages diurnally can make use of only a portion of the tidal cycle, which can limit fulfillment of energetic demands. Furthermore, daily and biweekly (spring–neap) tides may compound effects on shallow-water availability for foraging birds. However, the relative effects of daily and biweekly tidal periodicities on the foraging ecology of wading birds are seldom investigated due to a lack of appropriate tools. Therefore, we developed a tidal simulation model to provide dynamic spatiotemporal estimates of the availability of water depths that are within the upper and lower bounds of the birds' foraging water depth limits (“shallow-water availability”). We studied two wading bird species, the Little Blue Heron (Egretta caerulea), a daytime-only forager, and the Great White Heron (Ardea herodias occidentalis), which feeds both diurnally and nocturnally, to evaluate the relative effects of daily and biweekly tides on shallow-water availability and on patterns in abundance of foraging birds. Seasonal foraging surveys (n = 38; 2011–2013) were conducted by boat along a 14-km transect adjacent to extensive intertidal flats in the lower Florida Keys, USA. For both species combined, biweekly tides resulted in a 0.61- to 6.09-fold change in abundance, whereas daily tides resulted in a 1.03- to 5.81-fold change in abundance. Diurnal shallow-water availability was not consistently correlated in magnitude or direction with spring–neap tidal cycles because differences in tide height between consecutive low tides were larger than changes in tidal amplitude from spring–neap tide cycles. Thus, the strong response by birds to the spring–neap tide was likely driven by mechanisms other than diurnal shallow-water availability alone.
Ecomorphological differences in foraging and pattering behavior among storm-petrels in the eastern Pacific Ocean
Josh Sausner, Juan Carlos Torres-Mura, Jeanne Robertson and Fritz Hertel
For closely related species, differences in morphology can provide insight into the evolutionary history of a taxonomic group, as well as mechanisms for ecological segregation. Storm-petrels are among the smallest seabirds, and their greatest taxonomic diversity occurs in the eastern Pacific Ocean. Some storm-petrels exhibit a unique foraging behavior, known as “pattering” or “sea-anchor soaring,” in which they appear to walk on the surface of the ocean, but this behavior is used to a varying degree among species. We compared morphological traits related to the pattering behavior in 9 species of storm-petrels that breed in the eastern Pacific. Measurements on the wing (wing loading, aspect ratio), beak (size), and leg (length and foot size) were analyzed using a discriminant function analysis (DFA). A thin-plate spline/relative warp analysis was also used to detect subtle differences in wing shape. Species that patter the most have low wing loading, low foot loading, and a long tarsus and were distinct from the species that were classified as intermediate or least pattering. The DFA and a cluster analysis also identified putative pattering behavior of species based on morphology, for which there was little known observational data. A molecular phylogeny of the mitochondrial ND1 gene revealed that the 2 subfamilies of storm-petrels were not monophyletic. The phylogenetic tree shows that the pattering behavior has a strong evolutionary signal and arose early among storm-petrels.
Molecular analysis of nestling diet in a long-distance Neotropical migrant, the Louisiana Waterthrush (Parkesia motacilla)
Brian K. Trevelline, Steven C. Latta, Leesia C. Marshall, Tim Nuttle and Brady A. Porter
Elucidating the diet of Neotropical migratory birds is essential to our understanding of their ecology and to their long-term conservation. Reductions in prey availability negatively impact Neotropical migrants by affecting their survival as both nestlings and adults. Beyond broad taxonomic or morphological categories, however, the diet of Neotropical migrants is poorly documented. Using the molecular techniques of DNA barcoding and next-generation sequencing, we elucidated the diet of Louisiana Waterthrush (Parkesia motacilla) nestlings in Arkansas and Pennsylvania, USA. Waterthrush have been shown to respond negatively to the reduced availability of aquatic insects in the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT taxa). We hypothesized that Louisiana Waterthrush nestling diet would be primarily composed of these pollution-sensitive aquatic taxa, and that changes in the riparian insect community would be reflected in their diet. Unexpectedly, the orders Lepidoptera (92%) and Diptera (70%) occurred frequently in the diet of Louisiana Waterthrush nestlings. Among EPT taxa, only the order Ephemeroptera (61%) was frequently detected whereas Plecoptera (7%) and Trichoptera (1%) were poorly represented. The frequency at which aquatic Ephemeroptera and terrestrial Lepidoptera were detected in waterthrush nestling diet differed significantly over the nesting period in Pennsylvania but not in Arkansas, suggesting that phenological shifts in the availability of non-EPT prey taxa may be an important yet undescribed factor influencing the foraging ecology of waterthrush on the breeding grounds. Furthermore, these findings suggest that terrestrial insects may be more important to waterthrush nestlings than previously thought, which enhances our understanding of this biological indicator and Neotropical migrant.
Habitat quality and nest-box occupancy by five species of oak woodland birds
Megan C. Milligan and Janis L. Dickinson
Habitat quality can have important consequences for avian communities through impacts on survival and annual reproductive success. However, habitat quality is often hard to measure, leading to the use of occupancy as a proxy. We compared habitat use of 5 avian species that used nest boxes in the oak woodlands of central coastal California, USA, to determine which habitat characteristics best predicted box occupancy. We focused on the relationship between habitat characteristics and occupancy for five species—Ash-throated Flycatcher (Myiarchus cinerascens), House Wren (Troglodytes aedon), Oak Titmouse (Baeolophus inornatus), Violet-green Swallow (Tachycineta thalassina), and Western Bluebird (Sialia mexicana)—for which we had 12 consecutive years of data on nest boxes spread over a 700 ha study area. We also examined whether the physical habitat characteristics and box occupancy rates were good predictors of reproductive success, to infer whether they were useful indicators of habitat quality. The habitat characteristics influencing nest-box occupancy differed among the 5 species. Ash-throated Flycatchers were associated with fragmented habitats with less grassland. House Wrens were associated with riparian vegetation, as were Oak Titmice, which were also associated with chaparral. Violet-green Swallows were associated with chaparral but tended to nest farther from riparian corridors than Oak Titmice. Western Bluebirds nested away from riparian corridors and in areas with more grassland and oak woodland. Finally, occupancy rate was a better predictor than habitat characteristics of reproductive success, which suggests that occupancy can be a valuable proxy for habitat quality for these 5 species.
Effects of current reproductive success and individual heterogeneity on survival and future reproductive success of female Wood Ducks
Robert A. Kennamer, Gary R. Hepp and Bradley W. Alexander
Estimates of vital rates and their sources of variation are necessary to understand the population dynamics of any organism. These data have been used to test predictions of life history theory as well as to guide decisions of wildlife managers and conservation biologists. Life history theory predicts tradeoffs among life history traits, such that current reproductive effort will be negatively correlated with survival and/or future reproduction. Many studies support this prediction, but others report positive covariation between fitness traits, and attribute positive correlations to differences in individual quality. In this study, we used 11 yr of capture–mark–recapture data of breeding female Wood Ducks (Aix sponsa), along with their breeding histories, to examine sources of variation in annual survival rates and to assess the impact of current reproductive success on probabilities of survival and future reproductive success. Cormack-Jolly-Seber models indicated that apparent survival of female Wood Ducks did not vary annually and was only weakly affected by age class and breeding habitat conditions, but that there was a strong positive relationship between survival and the number of successful nests (0, 1, or 2). Next, we used a multistate analysis to examine the importance of female nest fate (successful or failed) on the probability of surviving and of nesting successfully the next year. Early incubation body mass was used to assess the nutritional status and quality of females. Females that nested successfully in year t were not less likely to nest successfully in year t + 1 than females that had nested unsuccessfully in year t. We also found strong positive covariation between nest success in year t and the probability of surviving. However, being in relatively good or poor condition had no effect on these relationships. Our results are consistent with the idea that female quality is heterogeneous, but body mass was not a good proxy of quality. Therefore, the existence of tradeoffs between female reproductive success and survival or future reproduction was less clear because of our inability to identify and control for differences in female quality.
Target enrichment of thousands of ultraconserved elements sheds new light on early relationships within New World sparrows (Aves: Passerellidae)
Robert W. Bryson Jr., Brant C. Faircloth, Whitney L. E. Tsai, John E. McCormack and John Klicka
Sparrows in the nine-primaried oscine family Passerellidae represent an attractive model for studying avian diversification across North and South America. However, the lack of phylogenetic resolution at the base of the New World sparrow tree has hampered the use of the existing sparrow phylogeny to test questions about the evolution of sparrow traits. We generated phylogenomic data from 1,063 ultraconserved elements to estimate phylogenetic relationships among the major clades of New World sparrows. Concatenated and species-tree analyses of 271,830 base pairs of sequence data converged on a well-supported phylogeny that differs from previous estimates. The resolved backbone of the sparrow phylogeny provides new insight into the biogeography of this radiation by suggesting both a tumultuous biogeographic history, with many colonizations of South America, and several independent ecological transitions to different habitat types.
Do migratory warblers carry excess fuel reserves during migration for insurance or for breeding purposes?
Jennalee A. Holzschuh and Mark E. Deutschlander
Migration is energetically costly, and many passerines prepare for and maintain migration with hyperphagia and increased fuel or fat reserves. During spring migration, as they approach their breeding grounds, passerines may deposit fat in excess of what is needed to complete migration. Individuals may carry excess fuel reserves as insurance against potentially poor environmental conditions in early spring (insurance hypothesis). If this is true, individuals arriving early at northern stopover locations or their breeding grounds should have greater energy reserves than later arrivals. Alternatively, passerines may arrive in spring with excess fat to help offset the demands of breeding (breeding performance hypothesis). Given the energetic requirements of egg production, females may arrive with greater reserves than males if excess fat directly or indirectly offsets breeding costs. We analyzed the energetic condition of 12 warbler species mist-netted during migration from 1999 to 2012 at Braddock Bay Bird Observatory, Monroe County, New York, USA. This northern stopover location is near the breeding range (in relation to total migratory distance) for most of the parulid species we examined and, therefore, is a likely location to show carryover effects between migration and breeding. In 11 of the 12 species, energetic condition was greater in the spring than in the fall for both sexes; and in all 12 species, condition was greater in females than in males in both seasons. Contrary to the insurance hypothesis, condition increased with arrival date for most species during spring migration. Although better condition in females supports the breeding performance hypothesis, the presence of this difference in both seasons suggests that additional factors influence energetic condition in parulids. Given that males arrive in better condition in the spring than when they depart in the fall, individuals of both sexes may carry excess energy reserves during spring migration to potentially use for reproductive efforts.
Variation in egg size, shell thickness, and metal and calcium content in eggshells and egg contents in relation to laying order and embryonic development in a small passerine bird
Grzegorz Orłowski, Lucyna Hałupka, Przemysław Pokorny, Ewelina Klimczuk, Hanna Sztwiertnia and Wojciech Dobicki
Although there are quite a number of studies examining the effect of egg laying order on the levels of elements and various chemical substances, none have taken into account the presence or absence of embryonic development in the eggs. In this study, we measured the morphometry (length, breadth, volume, and mass), shell thickness, and concentrations of calcium and 10 other metals (including 8 essential elements: chromium, copper, nickel, manganese, iron, cobalt, zinc, and magnesium; and 2 nonessential elements: lead and cadmium) in the shells and contents of embryonated and nonembryonated eggs across the laying order of Eurasian Reed-Warblers (Acrocephalus scirpaceus). We found a significant increase in egg volume in both nonembryonated and embryonated eggs, and an increase in egg length and mass in embryonated eggs, with laying order. Analysis confirmed significant differences related to laying order between nonembryonated and embryonated eggs in the concentrations of elements measured in shells (Cu, Cd, Pb, Mn, Fe, and Zn) and egg contents (Pb). Analysis of the relationships between laying order and concentrations of elements revealed a significant increase in Mg and Ca concentrations in the shells of embryonated eggs, and a significant decrease in Ni in the contents of nonembryonated eggs and in Cu, Cd, Mn, and Co in the contents of embryonated eggs. Our results indicate that laying order and the presence of an embryo are critical factors responsible for variation in some features of egg morphometry and element concentrations in eggshells and egg contents. These factors should therefore be taken into consideration in studies of the chemistry and morphometry of avian eggs.
Breeding biology of the Tropeiro Seedeater (Sporophila beltoni)
Márcio Repenning and Carla Suertegaray Fontana
The recently described Tropeiro Seedeater, Sporophila beltoni, is a rare long-distance austral migrant songbird that breeds in upland grasslands of southern Brazil. No aspect of its natural history has been studied previously. We studied the natural history of this seedeater in the grasslands of the Araucarian Plateau from 2007 until 2011, focusing on breeding biology and monitoring 133 nests. The breeding cycle lasts for 3.8 months, and the breeding season is correlated with photoperiod and phenology of the grasses; nesting peaks in November and December; the mean clutch size is 2 eggs (1–3); and only the females brood, for 12 days. The nestling period lasts 10 days, and both parents care for the nestlings, although with different roles. The daily estimated survival rate (DSR) of nests, as modeled by the MARK program, was 0.94 and varied temporally in the breeding season. The estimated reproductive success was 20%. The quadratic model best explained the changes in nest survival, coupled with concealment and nest height from the ground. Other factors tested, including year-to-year variation, age of the nest, and species of support plant, did not significantly affect nest survival. Predation was the main cause of nest failure (48%), followed by desertion of nests and trampling by cattle (37%). Multiple breeding attempts (maximum 3) occurred, averaging 1.75 (SE ± 0.17) nests per female in each breeding season. This information on breeding biology and nest survival will aid in management and conservation efforts in grasslands of southern Brazil.
Phenotypic and genetic analysis support distinct species status of the Red-backed Woodpecker (Lesser Sri Lanka Flameback: Dinopium psarodes) of Sri Lanka
Saminda P. Fernando, Darren E. Irwin and Sampath S. Seneviratne
Hybridization has challenged taxonomy, since hybridizing forms could be stable evolutionary entities or ephemeral forms that are blending together. The island of Sri Lanka has 2 subspecies of the flameback woodpecker D. benghalense: D. b. jaffnense in the north and D. b. psarodes in the south. Red plumage separates the endemic phenotype D. b. psarodes from other subspecies of D. benghalense. Despite these differences, intermediate phenotypes in north-central Sri Lanka discouraged the elevation of D. b. psarodes into a full species. The recent HBW and BirdLife International checklist, however, has elevated D. b. psarodes to a full species (D. psarodes), primarily based on its plumage. To objectively evaluate whether this taxonomic elevation is warranted, we examined the phenotypic and genetic affinities of D. psarodes within the D. benghalense cluster. In doing that we provide the first quantitative phenotypic and genetic analysis across a hybrid zone for an Old World woodpecker group. We sampled woodpeckers along a line transect across the island and measured body shape/size, plumage, and genetic variation in a mitochondrial gene (Cytb). Plumage color ranged from red in the south to yellow in the north, with varying proportions of orange in north-central Sri Lanka (an area of ~66 km). Morphology (body shape/size) and plumage characters showed a clear separation. There are 2 mitochondrial haplotype groups, one in the north and one in the south. A mixture of north and south haplotypes were seen in north-central Sri Lanka. Width of the hybrid zone suggests that some form of selection limits the spread of hybrids into the range of parental forms. Morphological, plumage, and genetic traits are all indicative of limited hybridization in a narrow zone between the 2 taxa, supporting the treatment of D. psarodes as a distinct species. This study provides an illustrative example of extensive hybridization between stable taxonomic entities, discouraging the practice of merging hybridizing forms as single species.
Interspecific competition for nests: Prior ownership trumps resource holding potential for Mountain Bluebird competing with Tree Swallow
Karen L. Wiebe
Interspecific competition over nest sites is common among cavity-nesting birds, but little is known about what determines the outcome of such contests, particularly whether or not prior ownership plays a role. Using a box removal and replacement experiment, I tested whether Mountain Bluebird (Sialia currucoides) or Tree Swallow (Tachycineta bicolor) had the higher resource holding potential (RHP). A different box-blocking experiment with paired boxes on territories measured the extent to which prior ownership influenced contest outcomes for both species. Behavioral observations in the pre-laying period showed more physical aggression by Mountain Bluebird against Tree Swallow. Nevertheless, Tree Swallow won 70% of boxes when neither species had prior ownership, suggesting Tree Swallow had a higher RHP. When their boxes were blocked, 24% of Tree Swallow usurped boxes from Mountain Bluebird, which did not differ statistically from the 33% of boxes usurped by bluebirds from swallows; thus, prior ownership does not guarantee winning the contest for either species. Currently, Mountain Bluebird arrives earlier in spring than does Tree Swallow and relies more extensively on prior ownership to retain nest sites. This advantage could be jeopardized if the migration schedule of Tree Swallow is accelerated due to climate change, and so it is important to understand the role of prior ownership in contests for nest sites for birds.
Range-wide patterns of geographic variation in songs of Golden-crowned Sparrows (Zonotrichia atricapilla)
Daizaburo Shizuka, M. Ross Lein and Glen Chilton
Discrete geographic variation, or dialects, in songs of songbirds arise as a consequence of complex interactions between ecology and song learning. Four of the five species of Zonotrichia sparrows, including the model species White-crowned Sparrow (Z. leucophrys), have been studied with respect to the causes and consequences of geographic variation in song. Within White-crowned Sparrows, subspecies that migrate farther have larger range size of dialects. Here, we assessed geographic patterns of song variation in the fifth species of this genus, the Golden-crowned Sparrow (Z. atricapilla). We analyzed field-recorded songs from 2 sampling periods (1996–1998 and 2006–2013) covering most of its breeding range in western North America. All songs began with a descending whistle and most songs consisted of 3–4 phrases that contained combinations of whistles, buzzes, and trills. We identified 13 discrete song types based on unique sequences of phrase types and frequency changes between phrases. Over 90% of individuals sang 1 of 5 song types, and we found clear dialect structure composed of these 5 common song types. The geographic range of dialects spanned large distances (500 to 1,700 km), resembling the geographic structure of dialects in the long-distance migrant Gambel's White-crowned Sparrow (Z. l. gambelli), though locations of dialect boundaries differ between species. Because both Golden-crowned Sparrows and Gambel's White-crowned Sparrows migrate similarly long distances, our study provides support to the hypothesis that dialect range size correlates with migration distance. We found little evidence of change in dialect composition in 4 populations that were sampled 15 years apart, which suggests that the dialect structure is stable across multiple generations. Our study opens the door for further comparisons to investigate links between ecology and the emergence of song dialects in this well-studied genus.
Viewing geometry affects sexual dichromatism and conspicuousness of noniridescent plumage of Swallow Tanagers (Tersina viridis)
Ana S. Barreira, Natalia C. García, Stephen C. Lougheed and Pablo L. Tubaro
Some types of plumage color are difficult to characterize spectrophotometrically because the properties of the reflected light change with viewing geometry (i.e. the relative positions of the light source and the observer, and the orientation of the feather). This is the case for the noniridescent plumage coloration of the Swallow Tanager (Tersina viridis), which seems to change from a human perspective as the angle between the light source and the observer varies. In this study, we measured plumage reflectance with different angles of illumination and/or observation, and used avian visual models to evaluate the change in sexual dichromatism and conspicuousness with viewing geometry from a bird's perspective. We also calculated different color parameters to assess how these changed with viewing conditions. Sexual dichromatism showed large changes, with its maximum coinciding with the angle combination between illuminant and observer that produced both the highest conspicuousness for males and the highest crypsis for females. The conspicuousness of males also varied with viewing geometry, and was consistently less when viewed by the visual system of a potential avian predator (VS) than by that of a conspecific (UVS). The change in perceived coloration was mainly related to large variation in hue and chroma in the plumage of males as the relative angle between the illumination and observation probes changed. Our results show that viewing geometry can alter color perception, even for noniridescent plumage coloration. Therefore, the relative position of the light source and the observer should be considered in studies of avian visual communication, particularly for species with plumage coloration similar to that of Swallow Tanagers.
Fifty-seventh Supplement to the American Ornithologists' Union
Check-list of North American Birds
R. Terry Chesser, Kevin J. Burns, Carla Cicero, Jon L. Dunn, Andrew W. Kratter, Irby J. Lovette, Pamela C. Rasmussen, J. V. Remsen Jr., James D. Rising, Douglas F. Stotz and Kevin Winker
Browse the Blog Posts
Or scan through the blog archive below for items of interest as only the latest post is shown below, thanks.