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Thursday, 8 January 2015

The Auk January 2015: Volume 132, Issue 1. TOC and Abstracts

The Auk

Published by: The American Ornithologists' Union

Table of Contents and Abstracts
Jan 2015 : Volume 132 Issue 1 

Tropical montane birds have increased nesting success on small river islands 

David Ocampo and Gustavo A. Londoño
Predation is the most important cause of nest failure in birds, and variation in predation risk has been associated with changes in nesting behaviors such as nest-site selection. Some birds choose favorable breeding sites on oceanic or large lake islands to increase their nesting success, but we do not know whether river islands with smaller water barriers provide similar “safe” conditions that decrease predation risk. We tested this in tropical birds by comparing daily survival rates (DSR; i.e. the probability that a nest will survive a single day) and predators identified at nests among bird species that nest on river edges and islands in the Andes. We monitored natural nests of 9 species and placed 70 artificial nests of different shapes (dome, cup, and ground nests) on islands and along river edges. We found that nest survival rates were greater on islands than on river edges for both natural nests (0.989 ± 0.004 vs. 0.0975 ± 0.004) and artificial nests (0.977 ± 0.007 vs. 0.944 ± 0.012). Isolation and nest height significantly explained (wi = 0.65) differences in DSR among islands and river edge. Among nest types, ground nests had higher DSR on islands and river edges than cup and dome nests. Birds were the principal predators in both areas, whereas small mammals, marsupials, and reptiles (i.e. snakes) preyed on nests exclusively on the river edges. Andean river islands—despite their small size and small distances from river edges—provided a refuge for nesting birds by isolating important nest predators such as mammals and snakes. Because birds that nest on islands have higher fitness, natural selection should favor individuals that select Andean river islands as nesting sites.
Abstract & References : Full Text : PDF (1331 KB) 

Birds build camouflaged nests Full Access

Ida E. Bailey, Felicity Muth, Kate Morgan, Simone L. Meddle, and Susan D. Healy
It is assumed that many birds attempt to conceal their nests by using camouflage. To our knowledge, however, no previous experimental studies have explicitly tested this assumption. To explore whether birds choose materials that match the background colors of nest sites to reduce the conspicuousness of their nests, we offered nest-building male Zebra Finches (Taeniopygia guttata) a choice of nest materials that either matched or did not match the color of their nest cup and the surrounding cage walls. Males chose to nest predominantly with material that matched the background color of the cage. To our knowledge, this is the first experimental evidence that birds actively select materials that camouflage their nests.
Abstract & References : Full Text : PDF (254 KB) 

Reproductive success of the specialist brood parasite Screaming Cowbird in an alternative host, the Chopi Blackbird Full Access

Alejandro G. Di Giacomo and Juan C. Reboreda
The Screaming Cowbird (Molothrus rufoaxillaris) is the most specialized brood-parasitic cowbird, relying almost entirely on the Bay-winged Cowbird (Agelaioides badius) as host. Recently, Screaming Cowbirds have expanded their range to areas where Bay-winged Cowbirds are absent, and they are exploiting the Chopi Blackbird (Gnorimopsar chopi). Interactions between Screaming Cowbirds and Chopi Blackbirds are largely unexplored, as is the reproductive success of the parasite in this host. Screaming Cowbirds, Chopi Blackbirds, and Bay-winged Cowbirds coexist in northeastern Argentina, providing an ideal system to explore interactions between a specialist brood parasite and an alternative host and to compare the reproductive success of the parasite in its main host and in an alternative host. Screaming Cowbirds parasitized both hosts throughout their breeding seasons (Chopi Blackbirds, mid-October to mid-January; Bay-winged Cowbirds, mid-November to mid-March). Frequency of parasitism was lower in Chopi Blackbirds than in Bay-winged Cowbirds (46% vs. 74%). Nest survival was higher in Chopi Blackbirds than in Bay-winged Cowbirds (37% vs. 15%). In successful nests, survival of Screaming Cowbird eggs and chicks was high and relatively similar in both hosts (Chopi Blackbirds: eggs, 99%; chicks, 90%; Bay-winged Cowbirds: eggs, 93%; chicks, 93%), but hatchability was lower in Chopi Blackbirds than in Bay-winged Cowbirds (52% vs. 92%). Considering (1) nest survival and (2) egg survival, hatchability, and chick survival in successful nests, the reproductive success of Screaming Cowbirds (i.e. proportion of eggs that resulted in fledglings) was 0.17 in Chopi Blackbirds and 0.12 in Bay-winged Cowbirds. Our results indicate that the Chopi Blackbird is a frequent host of the Screaming Cowbird, and parasitism of this alternative host may help explain the range expansion of this parasite in areas of Brazil where the Bay-winged Cowbird is absent.
Abstract & References : Full Text : PDF (485 KB) 

Spatial patterns in hydrogen isotope ratios in feathers of Burrowing Owls from western North America Full Access

Alberto Macías-Duarte and Courtney J. Conway
Deuterium (2H) has been used to track movements of land birds, under the assumption that δ2H in precipitation (δ2Hp) and δ2H in bird feathers (δ2Hf) are correlated across broad geographic gradients. The nature of this correlation has been evaluated only in a small percentage of the birds that breed in North America. We sampled Western Burrowing Owl (Athene cunicularia hypugaea) feathers of known origin (nestling feathers) at 36 locations throughout North America (from southern Canada to central Mexico). We used a modification of the “comparative equilibrium” technique of Wassenaar and Hobson (2003) to measure the δ2H of nonexchangeable hydrogen in feather samples. We characterized the strength of the relationship between δ2Hf and amount-weighted mean annual δ2Hp in a raptor that breeds in arid grasslands and deserts throughout western North America. We used a Bayesian hierarchical approach to model the δ2Hf–δ2Hp relationship, accounting for levels of intrinsic and extrinsic variation in δ2Hf. We found a linear relationship between δ2Hf and δ2Hp (δ2Hf = −13.48 + 0.78 δ2Hp; 95% credible interval (slope): 0.55–1.01) and used this relationship to construct a feather deuterium isoscape map. We observed relatively high levels of variation in mean δ2Hf across locations (SD = 11.01‰), due in part to variation in the contribution of precipitation to local food webs, and substantial variation among individuals within locations (SD = 6.68‰). Our data demonstrate that δ2Hf of juvenile Burrowing Owls can be used to infer local amount-weighted mean annual δ2Hp from the location of origin. Deuterium remains a valuable tool for tracking continental-scale raptor movements, with the caveat that researchers must identify and model for potential discontinuities in the δ2Hf–δ2Hp relationship in their inferences. However, isotopic discontinuities, coupled with a high relative abundance of individuals in those areas, can seriously hinder the usefulness of deuterium for identifying the origin of individual birds.
Abstract & References : Full Text : PDF (645 KB) 

Behavioral plasticity in nest building increases fecundity in marsh birds Full Access

Ellen P. Robertson and Brian J. Olsen
Many bird species nest in precarious, unpredictable locations to decrease the risk of predation. Although it is likely that many species have adapted behaviors to deal with stochastic habitats, there is currently limited evidence of plastic behavior increasing avian fecundity in the wild. Virginia Rails (Rallus limicola) and Soras (Porzana carolina) live in the littoral zones of wetlands that experience high hydrologic variability. During the summers of 2010 and 2011, we tested for the effects of hydrology and behavioral plasticity on the survival of Virginia Rail (n = 75) and Sora (n = 22) nests across 10 wetlands in Maine, USA. We identified the best predictors of both (1) nesting success at individual nests and (2) mean nesting success at the site level, using logistic-exposure models and an information-theoretic approach. Daily nesting survival was 98% for both species, and apparent nest survival was 31 of 85 nests, or 63.5%. Ninety percent of all nesting failures was from predation. Hydrology had a positive effect on nesting survival, and deeper, more variable water levels increased both individual nesting survival and mean site-level nest survival. Both species added material to their nests throughout the season in response to water-level increases, and we found that this behavioral plasticity had a positive effect on nesting survival. We caution that more variable water depths than those observed during our 2 yr of study could lead to increases in flood-related nest loss, because these birds require a delicate balance: the water must be deep enough to deter predators, yet shallow enough that they can build up their nests to prevent flooding during rain events. More information is needed on the extent of this behavior across marsh birds and other bird species.
Abstract & References : Full Text : PDF (407 KB) 

Life-history tradeoffs and reproductive cycles in Spotted Owls Full Access

Ricka E. Stoelting, R. J. Gutiérrez, William L. Kendall, and M. Zachariah Peery
The study of tradeoffs among life-history traits has long been key to understanding the evolution of life-history strategies. However, more recently, evolutionary ecologists have realized that reproductive costs have the potential to influence population dynamics. Here, we tested for costs of reproduction in the California Spotted Owl (Strix occidentalis occidentalis), and assessed whether costs of reproduction in year t − 1 on reproduction in year t could be responsible for regionally synchronized biennial cycles in reproductive output. Logistic regression analysis and multistate mark–recapture models with state uncertainty revealed that breeding reduced the likelihood of reproducing in the subsequent year by 16% to 38%, but had no influence on subsequent survival. We also found that costs of reproduction in year t − 1 were correlated with climatic conditions in year t, with evidence of higher costs during the dry phase of the El Niño–Southern Oscillation. Using a simulation-based population model, we showed that strong reproductive costs had the potential to create biennial cycles in population-level reproductive output; however, estimated costs of reproduction appeared to be too small to explain patterns observed in Spotted Owls. In the absence of strong reproductive costs, we hypothesize that observed natural cycles in the reproductive output of Spotted Owls are related to as-yet-unmeasured, regionally concordant fluctuations in environmental conditions or prey resources. Despite theoretical evidence for demographic effects, our analyses illustrate that linking tradeoffs to actual changes in population processes will be challenging because of the potential confounding effects of individual and environmental variation.
Abstract & References : Full Text : PDF (569 KB) 

The functional morphology of male courtship displays in the Pectoral Sandpiper (Calidris melanotos) Full Access

Tobias Riede, Wolfgang Forstmeier, Bart Kempenaers, and Franz Goller
The Pectoral Sandpiper (Calidris melanotos) is one of a few highly polygynous shorebirds with strong sexual size dimorphism. The vocal part of the male courtship display has received some attention, but how the sound is generated is largely unknown. To fill this gap, we analyzed video and sound recordings collected on the breeding grounds at Barrow, Alaska, USA. The anatomy of 2 males was investigated by macroscopic and histological dissection. Synchronized wing movements and a closed beak accompany hooting calls during flight displays. Courtship vocalizations on the ground include stereotypic beak and hyoid movements. We found a symmetric bipartite syrinx with songbird-like adduction and abduction mechanisms. Lateral and medial labia consisted of homogeneous extracellular matrix containing collagen fibers, which were only loosely organized, few elastin fibers, and a high proportion of hyaluronan. The upper vocal tract includes the trachea and an inflatable esophagus supported by thick and heavy skin over the ventral neck region. A highly organized network of fat and collagen makes this skin region relatively thick but also stretchable and robust. The hyoid skeleton was not distinctly different from that of pigeons, a group that also uses esophagus inflation to produce their characteristic sounds. These data lay a foundation for understanding the acoustic properties of the vocal signals used in territorial and courtship contexts.


Biological species and taxonomic species: Will a new null hypothesis help? (A comment on Gill 2014) Full Access

David P. L. Toews
In his article “Species taxonomy of birds: Which null hypothesis?”, Gill (2014) recommended that we might apply our growing knowledge of avian speciation more effectively, particularly to avian taxonomy and the definition of species. Specifically, Gill (2014) suggested that committees on avian nomenclature should operate under a new null hypothesis for species designation: Genetically and phenotypically distinct taxa would be considered full species, a priori, in the absence of any natural tests of reproductive isolation (i.e. sympatric populations) or additional evidence of possible isolating barriers. There are several useful aspects to this suggestion. However, in this Commentary, I present a number of issues that suggest that such a proposal may be premature. More generally, I recommend that unless a more compelling argument is made for altering the status quo, it seems prudent for nomenclature committees to continue to use the best available evidence to make informed decisions about the extent of reproductive isolation between putative avian species.
Abstract & References : Full Text : PDF (102 KB) 


Displaying to females may lower male foraging time and vigilance in a lekking bird Full Access

Sarah A. Cowles and Robert M. Gibson
Males of many species use courtship behavior to attract mates. However, by doing so males may face the associated costs of increased energetic expenditure, reduced foraging time, and elevated predation risk. We investigated the costs of display in lekking male Sharp-tailed Grouse (Tympanuchus phasianellus). We used lek-wide scan sampling to study how males allocated time among courtship display (“dancing”), agonism, foraging, and inactivity in relation to female numbers both within and across days. We also addressed the limited attention hypothesis and estimated visual attentiveness by videotaping 13 males and scoring head turns during these different activities. We found that the proportion of males engaged in display increased significantly with female numbers both within and across days. Additionally, foraging decreased with increasing female numbers both within and across days. Our results also suggested that agonism increased on days of high female attendance after females had left the lek. Males turned their heads only half as frequently during display as during other activities. These correlative data suggest two mechanisms by which display costs are potentially incurred: 1) a reduction in on-lek foraging time, and 2) reduced visual attention to the surroundings. It is possible that reduced foraging time and reduced vigilance during display may also be costs of increased courtship display in other nonlekking species.
Abstract & References : Full Text : PDF (386 KB) 

Quantitative color variation within and across morphs of the polymorphic White-throated Sparrow Full Access

Nathan A. Rathbun, Andrea S. Grunst, Melissa L. Grunst, Joanna K. Hubbard, Rebecca J. Safran, Rusty A. Gonser, and Elaina M. Tuttle
Coloration has evolved to serve diverse functions, including communication. In species with discrete color polymorphisms, the extent to which color variation exists within morphs and communicates multiple messages often remains unclear. We employed reflectance spectrometry to study variation in coloration in the dimorphic White-throated Sparrow (Zonotrichia albicollis), which exhibits a “white” and “tan” morph in both sexes. We explored whether distinct color traits distinguish between morph and sex classes, and whether color variation exists within classes that might reflect differences in individual quality. Further, we asked whether sexual dichromatism is more pronounced in the white morph, in which males display greater promiscuity and aggression and, thus, may be under stronger sexual selection for conspicuous coloration. Distinct aspects of crown plumage coloration differentiated the two morphs versus the two sexes and multiple types of coloration were associated with a morph, suggesting both multiple and redundant messaging functions of coloration. The brightness of white coloration and yellow carotenoid-based coloration differentiated the morphs, whereas the brightness and saturation of brown to black melanin-based pigmentation differentiated the sexes within morphs. However, coloration also varied considerably within morph and sex classes, potentially reflecting differences in individual quality. Finally, more sexual dichromatism existed within white morph than within tan morph birds. White morph males and females differed in white and yellow coloration, which also differentiated the morphs, and in melanin-based coloration. By contrast, tan morph males and females differed only marginally in coloration, and only in terms of melanin-based coloration. Results suggest that crown coloration is a multifaceted signal, and that selection has acted differently on coloration in both the morphs and the sexes. Our study suggests that multifaceted coloration can play multiple and redundant messaging functions, shows that color variation in polymorphic species can communicate more than morph, and suggests that morph-specific reproductive strategies alter selection on coloration.
Abstract & References : Full Text : PDF (455 KB) 

Autumn morning flights of migrant songbirds in the northeastern United States are linked to nocturnal migration and winds aloft Full Access

Benjamin M. Van Doren, Daniel Sheldon, Jeffrey Geevarghese, Wesley M. Hochachka, and Andrew Farnsworth
Many passerines that typically migrate at night also engage in migratory flights just after sunrise. These widely observed “morning flights” often involve birds flying in directions other than those aimed toward their ultimate destinations, especially in coastal areas. Morning flights have received little formal investigation, and their study may improve our understanding of how birds orient themselves during and after nocturnal movements and how they use stopover habitat. We studied autumn morning flights in the northeastern United States to identify associations between the number of birds undertaking morning flights and the magnitude of nocturnal migratory movements, nocturnal winds, and local topography. Our analyses included observations of more than 15,000 passerines at 7 locations. We found positive relationships between morning flight size and nocturnal migration density and winds aloft: Significantly more birds flew following larger nocturnal movements, quantified from weather surveillance radar and recordings of nocturnal flight calls, and after stronger nocturnal crosswinds. We also found consistent differences in morning flight size and direction among sites. These patterns are consistent with migrants engaging in morning flight as a corrective measure following displacement by nocturnal winds and to search for suitable stopover habitat.
Abstract & References : Full Text : PDF (370 KB) 

Comparative digesta retention patterns in ratites Full Access

Samuel Frei, Sylvia Ortmann, Christoph Reutlinger, Michael Kreuzer, Jean-Michel Hatt, and Marcus Clauss
Ratites differ distinctively in the anatomy of their digestive tracts. For example, Common Ostriches (Struthio camelus, hereafter Ostriches) have a particularly long, voluminous colon and long, paired caeca; Rheas (Rhea spp.) are characterized by a short colon with particularly prominent paired caeca; and Emus (Dromaius novaehollandiae) have neither prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97–123 kg), 5 Greater Rheas (R. americana, 22–27 kg), and 2 Emus (32–34 kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Greater Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species (Ostrich: 30–36 h; Greater Rhea: 7–19 h; Emu: 1.3–1.8 h), but there were no differences between the retention of 2 mm or 8 mm particles or a solute marker within species. The shape of the marker excretion curves corresponded to digesta mixing in the digestive tract of Ostriches and Greater Rheas but not Emus. The calculated dry matter gut fill (% of body mass) was significantly higher in Ostriches (1.6–1.8) than Greater Rheas (0.3–1.0) and Emus (0.2). Ostriches had the highest and Emus the lowest fecal dry matter concentration. These physiological findings match the differences in digestive anatomy and support the concept that in ratites, herbivory—and hence flightlessness—evolved repeatedly in different ways.
Abstract & References : Full Text : PDF (567 KB) 

The enigmatic Black Tinamou: Do distribution, climate, and vocalizations reveal more than one species? Full Access

Pablo Jose Negret and Oscar Laverde-R.
The Black Tinamou (Tinamus osgoodi) is a rare species with 2 recognized subspecies distributed locally. This is one of the most poorly known tinamous; few sound recordings exist, and few behavioral or sighting records are found in the literature or in ornithological databases. We compiled all the information on its geographic distribution and climate to provide a greater understanding of its current distribution. We also compiled all available sound recordings of the species in order to perform bioacoustic analyses to evaluate differences between subspecies. The 2 subspecies seem to be isolated by an ample distance, and each inhabits an area with a distinct climate. We also found some differences between their vocalizations. Future work should consider reevaluating the taxonomic status of the 2 subspecies. Conservation status of the resulting taxa must be reassessed, although more information on their ecology and natural history is needed.
Abstract & References : Full Text : PDF (459 KB) 

Dispersal and speciation in purple swamphens (Rallidae: Porphyrio) Full Access

Juan C. Garcia-R. and Steve A. Trewick
Dispersal, when accompanied by reduced gene flow and natural selection, influences speciation rates among groups of organisms. We used molecular phylogenetics, divergence time estimates, and population genetics to reconstruct the mode, pattern, and tempo of diversification within the wide-ranging purple swamphens (genus Porphyrio), with emphasis on the “supertramp” P. porphyrio. Our results suggest that the Porphyrioclade arose during the Middle Miocene in Africa, with a single colonization in the Americas and several other colonizations in Southeast Asia and the Indo-Pacific around 10 mya. We found that the widespread P. porphyrio is not monophyletic. Indeed, several subspecies and subspecies groups may represent species-level lineages. The P. p. melanotus lineage probably reached Australasia during the Pleistocene (600 kya), although some islands were colonized only in the past few hundred years. New Zealand, and some other islands, had previously been colonized (∼2.5 mya) by flying Porphyrio that evolved into flightless endemic species. Early and recent lineages are now sympatric. Widespread occupation of oceanic islands implies high dispersal and colonization rates, but gene flow probably occurs episodically and follows varying routes at different times. This pattern of colonization enables populations to differentiate and, ultimately, speciate.
Abstract & References : Full Text : PDF (660 KB) 


On the existence and potential functions of low-amplitude vocalizations in North American birds Full Access

Dustin G. Reichard and Joseph F. Welklin

Research on acoustic communication has focused predominantly on high-amplitude, long-range vocalizations that are easily recognized from a distance by the human ear. However, attention has recently expanded to the more enigmatic low-amplitude (quiet) vocalizations produced during close-proximity interactions associated with a variety of social behaviors such as aggression, courtship, group movements, and predator avoidance. The existence of low-amplitude vocalizations has been identified in a number of individual avian and nonavian species (e.g., crickets, fish, and primates), but how common these signals are within larger taxonomic groups such as orders and classes remains poorly understood. Here, we used the Birds of North America Online archive to perform a survey of the existence and putative functions of low-amplitude vocalizations across 749 species accounts of breeding birds in North America. By searching with keywords such as soft, quiet, low-amplitude, and whispered, we found evidence that 433 species (∼58% of those sampled) produce at least one type of low-amplitude vocalization. Low-amplitude calls were more commonly reported than low-amplitude songs, but both types of vocalizations were thought to be used around twice as often in courtship interactions as in aggressive interactions. Furthermore, 40% of species that sang low-amplitude songs produced at least one song that was thought to be divergent in structure from any high-amplitude songs in the species' repertoire; however, these acoustic differences were predominantly based on each author's auditory perceptions rather than on quantitative data. Collectively, these patterns suggest that low-amplitude vocalizations are common at a broad taxonomic scale, and that low-amplitude songs may be a distinct class of vocal signal. In addition, the observation that low-amplitude vocalizations are produced in a variety of social contexts, including courtship, indicates that these vocalizations should receive greater attention in future studies of communication, sexual selection, and social behavior.
Abstract & References : Full Text : PDF (206 KB) 


Migration and song elaboration in wood-warblers (Geothlypis) Full Access

Bruce E. Byers
Although some comparative studies of oscine songbirds have found that long-distance migration is positively correlated with elaborate songs, an analysis of singing by species in the genus Geothlypis (Parulidae) found no evidence of such a correlation. The migratory species in the genus sing relatively simple songs, whereas the singing of nonmigratory species varies; some species have simple songs, and others have more elaborate songs. Elaborate songs are found in the nonmigratory species G. semiflavaG. aequinoctialis, and G. poliocephala. For example, in Costa Rican populations of these species, songs are longer, contain more notes, have greater note-type diversity, and (in G. semiflava and G. aequinoctialis) have more phrase types than the songs of the migratory Geothlypis species. However, in other nonmigratory species (G. nelsoniG. flavovelataG. speciosa, and G. rostrata), the duration, note count, and note-type diversity of songs are similar to those of the migratory species. Thus, there seems to be no consistent relationship between migration and song elaboration in Geothlypis. In accordance with this inconsistency, ancestral-character-state reconstruction showed that evolutionary loss of migratory behavior was associated with increased song elaboration in some clades within the genus, but not in others. Overall, song variation in wood-warblers (Geothlypis) provides no support for the hypothesis that long-distance migration favors the evolution of elaborate songs.
Abstract & References : Full Text : PDF (557 KB) 

Morphological divergence in a continental adaptive radiation: South American ovenbirds of the genus Cinclodes Full Access

Jonathan A. Rader, Michael E. Dillon, R. Terry Chesser, Pablo Sabat, and Carlos Martínez del Rio
Cinclodes is an ecologically diverse genus of South American passerine birds and represents a case of continental adaptive radiation along multiple axes. We investigated morphological diversification in Cinclodes using a comprehensive set of morphometric measurements of study skins. Principal component analysis identified 2 primary axes of morphological variation: one describing body size and a second capturing differences in wing-tip shape and toe length. Phylogenetic analyses of the first principal component suggest an early divergence of Cinclodes into 2 main clades characterized by large and small body sizes. We suggest that 2 morphological outliers within these main clades (C. antarcticus and C. palliatus) may be cases of island gigantism and that a third (C. patagonicus) may reflect ecological character displacement. Despite its ecological and physiological diversity, the genus Cinclodes does not appear to show morphological diversity beyond what is typical of other avian genera.

Finding the best predictor of reproductive performance of Leach's Storm-Petrels Full Access

Morgan E. Gilmour, Christine R. Lattin, L. Michael Romero, Mark F. Haussmann, Robert A. Mauck, and Donald C. Dearborn
Physiological and environmental factors shape foraging strategies and energy balance. For species that breed seasonally, physiological changes in an individual can have short-term effects, but also can persist as carry-over effects from one season to the next, such as from the overwintering season to the breeding season. We tested the hypothesis that reproductive performance could be predicted by diet and energy balance during the breeding and nonbreeding seasons in a long-lived seabird, the Leach's Storm-Petrel (Oceanodroma leucorhoa). Specifically, we predicted that better reproductive performance would be correlated with four factors: (1) a high-lipid diet, as indexed by a high C:N ratio in stable isotope analyses; (2) a diet rich in antioxidants, as indexed by high plasma antioxidant capacity; (3) foraging at a high trophic level, as indexed by high values of δ15N in stable isotope analyses, which is positively related to lipids; and (4) a positive long-term energy balance, revealed by low levels of corticosterone in feathers. Because of our interest in short-term effects vs. carry-over effects, stable isotope values were measured from two different tissue sources: erythrocytes, to test for short-term effects, and winter-grown feathers, to test for carry-over effects. We monitored reproductive performance through egg volume, chick growth, parental provisioning, and fledging success. Parents with more breeding experience were more likely to have a successful nest in 2010, but not in 2009. Individuals exhibited consistent egg volume and nonbreeding season feather δ15N values across the 2 years of our study, but, overall, neither diet nor feather corticosterone predicted reproductive performance. Nonetheless, our simple, noninvasive measures of breeding performance could be applied to other species to study life-history strategies and energy balance.
Abstract & References : Full Text : PDF (489 KB) 

Corrosion casts: A novel application of a polyurethane resin (PU4ii) for visualizing eggshell pore morphology Full Access

Jason P. Murphy, Mark T. Swanson, William B. Jaeckle, and R. Given Harper
Avian eggshells serve the dual purposes of protecting the developing embryo from the external environment while also facilitating the loss of water vapor and the required exchange of CO2 and O2 gases. Pores that span the eggshell enable the loss of water and trans-shell gas exchange. Although knowledge of the geometry of these spaces is necessary to generate accurate estimates of the rate of gas diffusion across the shell, few techniques exist to obtain these data. Estimates of gas conductance across eggshells are typically calculated from eggshell thickness and the size and number of the pores on the exterior eggshell surface; the trans-shell pore spaces are assumed to be cylindrical in shape. To enable the testing of this assumption, we devised a novel method to visualize the three-dimensional morphology of eggshell pores using PU4ii, a polyurethane-based resin. Casts of the pores of eggshells of the domestic chicken (Gallus gallus) and House Sparrow (Passer domesticus) were unbranched and varied in diameter throughout their length, while casts of the pores of eggshells of the Ostrich (Struthio camelus) revealed a complex network of interconnected spaces. The simplicity of this technique and the stability and resilience of the resulting casts provide opportunities to predict gas flux across the shell and to evaluate the morphology of eggshell pores among birds from different taxonomic groups.
Abstract & References : Full Text : PDF (365 KB) 

Conservative and opportunistic settlement strategies in Arctic-breeding shorebirds Full Access

Sarah T. Saalfeld and Richard B. Lanctot
Shorebirds seem to have evolved a number of strategies for adapting to and exploiting the unpredictable and inhospitable Arctic environment. Two such strategies put forth by Holmes and Pitelka suggest that species either conservatively or opportunistically select breeding locations based on local environmental conditions. “Conservative” species were characterized by strong site fidelity and territoriality, consistent population densities, relatively even spacing of individuals, and monogamous mating systems, while “opportunistic” species exhibited opposite traits and were polygamous. Here, we assessed whether 10 shorebird species consistently exhibited these settlement strategies over a 10-year period (2003–2012) near Barrow, Alaska, by comparing annual estimates of site fidelity, territoriality, and population density. Additionally, we determined the relative importance of past and current environmental and social conditions in predicting annual breeding densities of these same species. Data from 1,413 captured adults and 1,946 shorebird nests indicated that most species conformed to 1 of the 2 settlement strategies, while others exhibited traits of both strategies, and a few had settlement patterns inconsistent with that predicted for their mating system. We suggest that deviations from these strategies may occur depending on a species' location within its breeding range. For some species, however, described settlement patterns may be too simplistic. Species with the same settlement strategy seem to respond similarly to environmental cues but differently than species with the alternative strategy. However, we were unable to determine a common environmental cue for species with the same settlement strategy, although lemming abundance, overall nest survival rate, and presence of conspecifics or heterospecifics did seem to influence settlement decisions in some species. Results from this study indicate that understanding how species settle may have important consequences for implementing monitoring or conservation actions.
Abstract & References : Full Text : PDF (905 KB) 

Drought-caused delay in nesting of Sonoran Desert birds and its facilitation of parasite- and predator-mediated variation in reproductive success Full Access

Chris McCreedy and Charles van Riper, III
As our understanding of climate change has increased, so has our awareness of the impacts of these changes on biotic systems. Climate models are nearly unanimous in their predictions for increased drought frequency in southwestern North America, and delays in nest initiation due to drought may influence nesting success and productivity for many Sonoran Desert bird species. In southeastern California and western Arizona in 2004–2009, we found negative correlations for 13 of 13 species between nest initiation date and rainfall accumulation during the preceding 4-month winter rainy season. Nesting was delayed more than 3 weeks for some species during extreme droughts in 2006 and 2007. During 2004–2009, we found a significant negative effect of nest initiation date on nest survival probability (β̂ = −0.031 ± 0.005 SE, P < 0.001) for the four species of greatest sample size. To investigate the role of nesting delay in nesting success and productivity, in 2010 we conducted a manipulative experiment with Black-tailed Gnatcatchers (Polioptila melanura; BTGN) and Verdins (Auriparus flaviceps; VERD). Following a wet winter, we delayed clutch initiation dates for treatment pairs to match first-egg dates that we observed during droughts in 2006 and 2007. Nest initiation date had a significant negative effect on nest survival of both species (BTGN: β̂ = −1.18 ± 0.27 SE, P < 0.001; VERD: β̂ = −2.33 ± 0.51 SE, P = 0.003). Treatment pairs were unable to overcome the lost period of high productivity in March and early April, and had lower productivity than control pairs over the entire breeding season. As nest predation and Brown-headed Cowbird (Molothrus ater) parasitism were the most common causes of nest failure, we conclude that the impacts of climate change–caused drought on annual reproductive output in the Sonoran Desert will be further compounded by parasitism and predation for Black-tailed Gnatcatchers and by predation for Verdins.
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Divergence in morphology, calls, song, mechanical sounds, and genetics supports species status for the Inaguan hummingbird (Trochilidae:Calliphlox “evelynae” lyrura) Full Access

Teresa J. Feo, Jacob M. Musser, Jacob Berv, and Christopher James Clark
The Bahama Woodstar (Calliphlox evelynae), a hummingbird endemic to the Bahama Archipelago, comprises two currently recognized subspecies:Calliphlox e. evelynae, found throughout the Bahamas and in the Turks and Caicos Islands, except on Great and Little Inagua; and C. e. lyrura, named for its unique, lyre-shaped outer tail feathers and found only on the islands of Great and Little Inagua. The two were originally described as separate species, partly on the basis of their divergent tail morphology, but were subsequently lumped by Peters (1945). These taxa are members of the North American “bee” hummingbird clade, which produce mechanical sounds with their tails during courtship displays. Changes in tail shape may produce significant acoustic divergence. To determine the extent of differentiation between lyrura and evelynae, we collected field recordings of calls, songs, and courtship displays from New Providence and Great Inagua islands and surveyed morphological variation across the archipelago. We sequenced 4 nuclear loci and 2 mitochondrial genes from 9 individuals of evelynae and 6 individuals of lyrura. Both sexes of lyrura andevelynae can be diagnosed by vocal calls, and males can be diagnosed by morphology, song, and courtship display. Phylogenetic reconstructions based on the genetic data indicate that the 2 populations are reciprocally monophyletic and that they diverged ∼0.69 mya. Our data indicate thatlyrura is a unique evolutionary lineage that warrants species status under both the phylogenetic and the biological species concept.

The importance of site to mate choice: Mate and site fidelity in Piping Plovers Full Access

Meryl J. Friedrich, Kelsi L. Hunt, Daniel H. Catlin, and James D. Fraser
Each breeding season, seasonally monogamous birds can divorce or reunite with their previous year's mate, assuming both partners survive and return. We tested a suite of variables related to mate choice and site choice to determine which of 4 prominent mate fidelity hypotheses (better [mate] option, habitat mediated, musical chairs, and bet-hedging) best explained the interyear reunion rate and breeding dispersal of a seasonally monogamous shorebird, Piping Plover (Charadrius melodus), nesting on dynamic sandbars on the Missouri River, USA, 2005–2012. Of 252 pairs in which both members returned to the breeding grounds the following year, only 20% reunited. Pairs with an early-arriving male had the highest mate fidelity. Reunited pairs returned to previous nest sites (median breeding dispersal = 39 m), and divorced and widowed birds tended to move farther (median = 229 m and 193 m, respectively). Overall, site fidelity was higher in males than females. Previous reproductive success of a pair did not predict reunion, but all successful birds, with the exception of divorced females, exhibited high site fidelity, suggesting selection for site based on prior breeding success. Among divorced birds, females had higher-quality mates and higher nest success compared to their former partners, and they nested in areas of similar quality between years, whereas males settled in lower-quality areas following divorce. The benefits that females gained from divorce suggested that females initiated divorce to improve reproductive success, which supports the better option hypothesis. Although females seemed to initiate most divorces, males may have divorced as a safeguard against remaining unmated when there was uncertainty about the survival and return of a former mate, as proposed by the bet-hedging hypothesis.
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Digital photography quantifies plumage variation and salt marsh melanism among Song Sparrow (Melospiza melodia) subspecies of the San Francisco Bay Full Access

Sarah A. M. Luttrell, Sara T. Gonzalez, Bernard Lohr, and Russell Greenberg
Local adaptation is often implicated as a driver of speciation and diversity, but measuring local variation within a species can be difficult. Many taxa endemic to salt marshes exhibit a phenotypic trait called salt marsh melanism, in which salt marsh endemics have a darker or grayer integument than their freshwater congeners. The repeated occurrence of salt marsh melanism across distantly related taxa in similar environments suggests a role for local selection in maintaining this trait. We quantitatively explored variation in plumage characteristics for four subspecies of the Song Sparrow (Melospiza melodia) in the San Francisco Bay area. These subspecies are restricted to habitats of varying salinity and climate, and are considered a classic example of ecologically based variation on a local scale. To analyze plumage color, we employed a digital photographic technique which was quantitative, able to deal with pattern variation, and independent of a particular visual system. Although no single plumage measure distinguished among all four subspecies, combining the measures allowed reliable assignment of most specimens. Using a discriminant analysis with five measures of plumage color, we were able to classify 75% of specimens to the correct subspecies, well above the 25% correct classification expected due to chance. The three subspecies inhabiting more saline environments (M. m. pusillula, M. m. samuelis, and M. m. maxillaris) were either darker (lower luminance) or grayer (lower red dominance) than the inland subspecies M. m. gouldii, supporting the pattern of salt marsh melanism observed in other taxa.
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Paving the way: Multifunctional nest architecture of the Rock Wren Full Access

Nathanial Warning and Lauryn Benedict
Some avian species augment nest cups by building associated architectural structures that may mitigate predation, parasitism, and/or hatching failure. Because effective nest construction is integral to reproductive success, architectural structures associated with nests are predicted to provide functional benefits. Rock Wrens (Salpinctes obsoletus) stereotypically augment their soft cup nests with a pavement of stones, apparently incurring considerable energy costs. We quantified Rock Wren stone use and measured how stones occlude nest cavities. We examined whether Rock Wrens adjust individual stone-carrying effort in response to nest cavity opening size and tested 3 hypotheses about the benefits of cavity occlusion: (1) stones ameliorate temperature fluctuations and improve nest thermoregulation; (2) stones improve nest microclimates by keeping them dry; and (3) stones have the potential to reduce nest predation by alerting incubating females when predators approach. We found that individual nest pavements contained up to 1.4 kg of stones, which varied in size but were relatively uniform in thickness. Stone pavements decreased nest cavity openings by a mean of 34%, with larger openings containing significantly more stones. Presence of stones did not influence temperature in unoccupied nest cavities but did significantly decrease water infiltration into the nests during simulated rainfall. Presence of stones also changed the sound of a simulated predator approach, supporting the idea that stone patios could serve as an alarm function for vulnerable incubating females. Our data indicate that Rock Wrens adjust the amount of stones used in nests according to cavity characteristics to obtain multiple benefits. Results confirm that nest site modification can be an adaptive behavior and provide evidence that birds facultatively modify nesting environments.
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Patterns of diversification in small New World ground doves are consistent with major geologic events Full Access

Andrew D. Sweet and Kevin P. Johnson
South America has undergone many dramatic changes during the past 60 million years, which has had a major impact on the patterns of biological speciation and diversity in the region. Birds have been particularly affected, and major geologic events have been an important factor in generating avian diversity in the New World. Here we investigate the impact of two geologic events, Andean uplift and the Panamanian land bridge formation, on the speciation and diversification patterns of birds in the New World using a broadly dispersed clade, the small New World ground doves (Aves: Columbidae). Using complete species-level sampling for the clade (barring 2 possibly extinct species), we used sequences of 4 mitochondrial genes and 1 nuclear gene to infer a phylogenetic tree for the group. To address historical biogeographic questions, we estimated divergence times and reconstructed ancestral ranges. The phylogenetic analysis resulted in a well-supported tree. Divergence time estimates and historical biogeographic reconstruction indicated a South American origin for the clade, with several speciation events coinciding with either Andean uplift events or the land bridge formation. These results indicate how major geologic events affected the diversification of this group of birds, and lead to a broader understanding of the impact of these events on patterns of speciation in New World birds.

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