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Tuesday, 9 September 2014

The Wilson Journal of Ornithology; September 2014 : Volume 126 Issue 3. Contents and Abstracts

The Wilson Journal of Ornithology

Published by: The Wilson Ornithological Society




Table of Contents

September 2014 : Volume 126 Issue 3 

MAJOR ARTICLES

Sexual plumage dichromatism in a size monomorphic seabird Full Access

Stefanie M. H. Ismar, Claire Daniel, Branislav Igic, Peter K. Morrison-Whittle, Grant Ballard, Craig D. Millar, Andrew E. Fidler, Kevin J. McGraw, Kazumasa Wakamatsu, Brent M. Stephenson, Phillip Cassey, Donald C. Dearborn and Mark E. Hauber,
pg(s) 417–428
Abstract
Data on the extent to which the sexes may differ in their phenotypes are critical for a full understanding of the biology and management of any species. We previously quantified behavioral differences and vocal similarities between genetically-sexed Australasian Gannets (Morus serrator). Here, we quantify size monomorphism and plumage dichromatism in this socially monogamous, colonial seabird. In comparison with other sulids, the Australasian Gannet is characterized by low sexual dimorphism indices in various size metrics, and most physical dimensions are statistically similar between adult female and male gannets. In contrast, we found indications of sexually dichromatic plumage traits in the melanin-based, rusty head plumage and in the black-and-white tail feathers. To our knowledge, these findings constitute the first evidence of melanin-generated sexual plumage dichromatism in a size monomorphic seabird species. Using opsin-sequencing, we also confirm that the Australasian Gannet is a visually violet-sensitive species, for which the detection of both gross differences in feather reflectance, and long-wavelength based plumage dichromatism, should be perceptually feasible. However, because of the extensive overlap between females and males in the size and chromatic traits detected here, and in the behavioral and vocal displays reported in previous studies, we advocate for the use of genetic techniques for sex identification in this gannet species.
Abstract & References : Full Text : PDF (3523 KB)


Genetics of a high-latitude cryptic speciation event: American and Pacific golden-plovers Full Access

Jack J. Withrow and Kevin Winker
pg(s) 429–442
Abstract
Diversification during the Pleistocene is thought to have contributed significantly to taxonomic diversity at high latitudes. In some cases this diversity is cryptic, in that speciation has occurred with little change in phenotype. We examined the genetic signatures of one such case, between American and Pacific golden-plovers (Pluvialis dominica and P. fulva, respectively). This high-latitude species pair is morphologically very similar, and they are obligate long-distance migrants. They were only relatively recently recognized as separate species. We used 1,041 bp of the mitochondrial gene NADH dehydrogenase subunit 2 (ND2) from 20 dominica and 22 fulvaand 242 amplified fragment length polymorphisms (AFLPs) from 29 individuals of each species sampled from sympatric and allopatric breeding populations to assess the levels of divergence, divergence date, and gene flow. A divergence date of ∼1.8 mya was estimated, and although we detected a seemingly old hybridization event, very little gene flow was detected (effectively zero). Significant genetic divergence was found between species (4.7% uncorrected sequence divergence in mtDNA; FST  =  0.21 in AFLPs). We suggest that ecological factors and possibly sexual selection acted to limit gene flow during the divergence of these cryptic species during the Pleistocene, but given the age of the split we could not determine the mode of speciation that occurred.
Abstract & References : Full Text : PDF (1049 KB) 


Daily survival rate for nests of Black Skimmers from a core breeding area of the southeastern USA Full Access

Gillian L. Brooks, Felicia J. Sanders, Patrick D. Gerard, and Patrick G. R. Jodice
pg(s) 443–450
Abstract
Little is known about the reproductive success of Black Skimmers (Rynchops niger) throughout the southeastern USA where availability of undisturbed beaches for nesting is limited. Daily survival rates (DSR) of nests were examined at three nesting sites in Cape Romain National Wildlife Refuge (CRNWR), South Carolina, USA, 2009–2010. The percent of successful nests (n  =  346 nests) ranged from 42–69% among colony sites when data were pooled across both years. The DSR of nests was primarily related to colony site, predation risk, height of high tide, and clutch size. Predation and overwash were the principal causes of identifiable nest loss, each accounting for ∼33% of nest failures during the two study years. Because of the challenges of resighting skimmer chicks, we were not able to measure chick survival effectively and therefore accurate measures of productivity remain elusive. High variability in nest success among sites within close proximity to each other (<20 km) suggests factors at local scales such as disturbance, predation, and overwash events strongly influenced nest success of Black Skimmers during these 2 years as opposed to more region-wide stressors such as tropical storms or food availability. Although time-intensive techniques to control predators do exist, management options to limit flooding and overwash are far more limited. Conservation of Black Skimmers in the southeastern USA would benefit from coordinated, multi-state efforts to measure nest and chick survival.


Thamnophilidae (antbird) molt strategies in a central Amazonian rainforest Full Access

Erik I. Johnson and Jared D. Wolfe
pg(s) 451–462
Abstract
Avian molt, or the regularly scheduled replacement of feathers, is an important life history event, particularly in central Amazonian rainforest birds for which a relatively high proportion of the annual cycle can be dedicated to this process. Here, we detail molt strategies of 18 antbird species (Thamnophilidae) based on 2,362 individuals captured from lowland tropical rainforest at the Biological Dynamics of Forest Fragmentation Project near Manaus, Brazil. All species exhibited a molt strategy consistent with the Complex Basic Strategy, in which birds undergo an inserted preformative molt within the first cycle, but apparently lack prealternate molts. The preformative molt and resulting formative plumage aspect of the 18 antbird species can be grouped by three distinct patterns: 1) a complete molt resulting in an adult-like formative plumage without molt limits; 2) a partial molt involving body feathers, lesser coverts, at least some or all median and greater coverts, and sometimes tertials or rectrices, resulting in an adult-like formative plumage with molt limits; and 3) a partial molt as in ‘2’ but resulting in an adult female-like formative plumage in both sexes with plumage maturation delayed in males until the second prebasic molt. In addition, we show that one species, Percnostola rufifrons, exhibited an extra inserted molt (a partial auxiliary preformative molt) in the first cycle before initiating a complete preformative molt making this, to our knowledge, the first description of an auxiliary preformative molt for a suboscine. The extent of the preformative molt or delayed plumage maturation was not predicted by ecological guild, raising questions about how phylogenetic relatedness and ecological adaptation drive variation in molt patterns across antbirds.
Abstract & References : Full Text : PDF (5561 KB)


Nesting biology of the Black Antbird (Cercomacroides serva) Full Access

Camilo Flórez-V and Gustavo A. Londoño
pg(s) 463–473
Abstract
The Black Antbird (Cercomacroides serva) inhabits the east Andean foothills and Amazonian lowlands from Colombia to north Bolivia and western Brazil. It is uncommon throughout its distribution. We provide the first nest and egg description for C. serva with detailed information on bi-parental incubation and nestling feeding behavior. We found four nests at two elevations in the buffer zone of Manu National Park in southeastern Peru. The C. serva nest is a pensile hanging cup, much higher at the back that at the front, made with dark fibers, dry leaves, sticks and fresh moss. The entrance was strongly oblique in three of the four nests. Egg coloration varied between and within the two eggs clutch size. On average, parents made 5.7 ± 2.08 (±SD) foraging trips per day that lasted 39.2 ± 36.17 mins, resulting in 84.6 ± 9.2% nest attentiveness. Both sexes share daytime incubation, but night incubation was exclusively conducted by the female. Nest attentiveness did not differ between males and females, but daytime incubation bouts did vary between the sexes. Afternoon incubation was mainly conducted by the female (77.7%); in contrast, morning incubation was conducted primarily by the male (66.1%). The nestling period was 12–14 days, and the female spent more time feeding and brooding the nestling, a behavior that differs from that of other antbirds. Overall, nesting characteristics of C. serva resemble previous reproductive information published for otherCercomacroides species
Abstract & References : Full Text : PDF (16455 KB)


Do Nearctic migrant birds compete with residents at army ant raids? A geographic and seasonal analysis Full Access

Sean O'Donnell, Anjali Kumar, and Corina J. Logan
pg(s) 474–487
Abstract
Army ant swarm raids in Neotropical montane forest are attended by diverse flocks of foraging birds that can include residents year-round and overwintering Nearctic migrants. We asked whether migrants and residents affect each other's ability to forage at army ant raids. We quantified variation in raid attendance by three guilds of birds: wintering migrants, regular and obligate raid attending residents (ant-following residents), and facultative raid attending residents. To test whether wintering migrants and residents were negatively associated at raids, we collected data on raid attendance in four adjacent life zones in the Tilarán Mountains of Costa Rica and in different seasons (when migrants were present and absent). We first compared the guilds' raid attendance among life zones. There was little geographic overlap of migrants and ant-following residents at raids, and raid attendance frequencies were strongly correlated with the estimated local abundances of these bird guilds in each life zone. We then analyzed resident bird flock size and species makeup in the life zones where migrants attended raids most often (Premontane and Lower Montane Wet forests). If migrants affected raid attendance by facultative resident birds, we expected resident numbers or species richness at raids to decrease with migrant presence. Resident flock size and species richness did not differ between times of year with and without migrants, and species identities differed little between seasons. Furthermore, resident flock composition in migrant presence season was similar at raids with and without migrants. We conclude migrants had no measurable effect on resident bird army ant exploitation. Migrants were smaller on average and less likely than residents to capture prey from the ground at raids. These body size and foraging substrate differences between residents and migrants may mitigate inter-guild competition for food at raids.


Variation in antiparasitic behaviors of Red-winged Blackbirds in response to simulated Brown-headed Cowbirds Full Access

Carol S. Henger and Mark E. Hauber
pg(s) 488–499
Abstract
Red-winged Blackbirds (Agelaius phoeniceus) are a frequently parasitized host species of obligate brood parasitic Brown-headed Cowbirds (Molothrus ater). Yet, this common host does not reject parasite eggs or young. A hypothesis to explain the lack of cowbird egg and nestling rejection is that redwings frontload their responses by investing into antiparasitic nest defense behaviors toward female cowbirds, relative to non-laying male cowbirds and non-threatening other species. A review of prior studies using cowbird-mount presentations with or without acoustic playbacks supported some but not all predictions of this hypothesis. We conducted a new study at two geographically separate sites, in New York City, NY and in Ithaca, NY, USA, where Red-winged Blackbirds were presented with taxidermic models on a tripod and species- and sex-specific vocalization playbacks of female or male Brown-headed Cowbirds, female Northern Cardinals (Cardinalis cardinalis), or a tripod and silence (control). Reactions of both sexes to mount and playback presentations near known, active nests, conducted repeatedly throughout the breeding cycle, were supplemented with mount and playback presentations to males without known nests. Red-winged Blackbirds responded more aggressively toward presentations of both sexes of the parasite than to the cardinal and the tripod treatments. In addition, they responded more aggressively at known nests to mounts presented closer rather than farther, and at nests with nestlings rather than eggs. Furthermore, aggressive reactions were more frequent in Ithaca, NY than in New York City, NY. Finally, the reactions of female and male redwings near known active nests and of males without known nests showed statistically similar patterns, implying that data from these two types of experimental contexts could be combined in our analyses, and perhaps in future studies, to more efficiently characterize this host's responses to parasite presentations.


Dawn singing of Eastern Phoebes varies with breeding stage and brood number Full Access

Adrianna Bruni and Jennifer R. Foote
pg(s) 500–507
Abstract
The dawn chorus is a daily period of continuous singing by male songbirds that begins prior to sunrise. It is relatively less studied than daytime singing, and particularly in suboscine birds. We analyzed dawn singing of 14 Eastern Phoebes (Sayornis phoebe) in Echo Bay, Ontario over the 2011–2012 breeding seasons. We measured time of first song, length of dawn bout, time of final song, average song rate, and peak song rate and compared these characteristics among breeding stages. Results indicated that breeding stage was a significant predictor of all five dawn song features. Our results suggest that dawn singing of Eastern Phoebes is directly related to female fertility. We show that males begin singing significantly earlier when females are fertile. Males sang significantly longer during fertile and incubation stages than while feeding young. Males began singing later and sang for the shortest duration during the pre-breeding period. Song rates were higher in first broods than in second broods. We showed that suboscine dawn signaling patterns vary across breeding seasons in ways similar to oscine songbirds.


Male House Wrens provide more parental provisioning to nests with a brighter artificial egg Full Access

Lindsey A. Walters, Nathan Olszewski, and Kevin Sobol
pg(s) 508–515
Abstract
Recent research suggests that male birds could use eggshell color as a signal of the quality of their offspring to decide how much parental care to provide. Previous studies have found support for this hypothesis in bird species that lay blue eggs, but it has not been as thoroughly tested in species that lay brown eggs, such as House Wrens (Troglodytes aedon). In this species, brighter eggs are associated with greater female investment. We tested whether males responded to this potential cue. We experimentally manipulated clutch brightness by randomly adding a white or brown plastic egg to nests during incubation and then compared the male provisioning rates between those two treatment groups. Male House Wrens whose nests had received a white egg provisioned their nestlings at significantly higher rates than males whose nests had received a brown egg. These results suggest that male House Wrens pay attention to female investment when deciding how much energy to spend on nestling provisioning. This study supports the generality of the hypothesis of egg color as a sexually selected signal by experimentally demonstrating that males of a species that lays brown eggs also can respond to egg color.


Breeding dispersal of Mexican Spotted Owls in the Sacramento Mountains, New Mexico Full Access

Joseph L. Ganey, Darrell L. Apprill, Todd A. Rawlinson, Sean C. Kyle, Ryan S. Jonnes, and James P. Ward Jr.
pg(s) 516–524
Abstract
Dispersal is a key process influencing population dynamics and gene flow in species. Despite this, little is known about breeding dispersal in threatened Mexican Spotted Owls (Strix occidentalis lucida), here defined as movement of a non-juvenile owl between territories where it had the opportunity to breed. We observed 28 cases of breeding dispersal during a study of color-banded Mexican Spotted Owls in the Sacramento Mountains, New Mexico, 2003–2011. This represented 4.9% of total opportunities to disperse (n  =  575 observed occasions, range  =  0–9.0% of owls dispersing per yr). Breeding dispersal probability was greater for single owls and paired owls whose mate disappeared or moved than for paired owls whose mate remained in the original territory, greater for subadult than for adult owls, and greater for owls that failed to reproduce the year prior to dispersing than for owls that reproduced successfully. There was some evidence that dispersal probability was greater for female owls and that females dispersed greater distances than males, but dispersal distances generally were small for both sexes of owls (mean distance  =  5.1 and 3.6 km for females and males, respectively). All dispersing owls were paired the first year they were observed in their new territory. Breeding dispersal appeared to occur regularly but at relatively low levels in this population, and dispersal probability appeared to be associated with owl social status, reproductive status, and age prior to dispersal. Because most dispersing owls either were unpaired or lost their mate, and because most failed to reproduce the year prior to dispersal, these owls generally were able to improve their social status and reproductive success by dispersing.


Effect of food availability and habitat characteristics on the abundance of Torrent Ducks during the early breeding season in the central Andes, Argentina Full Access

Leandro M. Álvarez, Andrea A. Astié, Guillermo O. Debandi, and Erica E. Scheibler
pg(s) 525–533
Abstract
Torrent Ducks (Merganetta armata) inhabit rivers and streams across the Andes. The species feeds mainly on aquatic invertebrates and occurs in rivers with high flow rate, large emergent rocks, and low anthropogenic disturbance. The objective of this work was to study the effect of food availability and environmental variables on the abundance of Torrent Ducks in two streams with different levels of anthropic disturbance and diverse environmental conditions. To describe each stream, we recorded density and richness of benthic macroinvertebrates and physical-chemical variables, and characterized the stream habitats. We also censused the number of Torrent Ducks present in each stream. We prepared a principal component analysis to portray features of each stream. Generalized linear models were used to estimate which environmental variables were associated with the ducks' abundance and to explore variations in biotic variables between streams and between sections within each stream. We recorded 40 individuals in the stream with the lowest disturbance (Arroyo Grande) and four individuals in the most highly disturbed stream (Río Blanco). Variation in abundance of Torrent Ducks was better explained by a higher density of Notoperla, Plecoptera (an aquatic insect associated with clean waters) and to a lesser extent by flow rate.


Conspecific effect on habitat selection of a territorial cavity-nesting bird Full Access

Claudio S. Quilodrán, Cristián F. Estades, and Rodrigo A. Vásquez
pg(s) 534–543
Abstract
The simulated presence of conspecifics has been proposed to attract territorial songbirds to protect nesting areas when the habitat is being disturbed by human activities. We studied the effects of conspecifics on the nest-site selection of the Thorn-tailed Rayadito (Aphrastura spinicauda; Furnariidae), a forest songbird that depends on cavities for nesting. Plantations represent usable habitat for foraging, but the scarcity of cavities restricts their use during the breeding period. The use of nest boxes is a documented measure to mitigate the negative effect of plantations on cavity users. We installed nest boxes in a plantation of Pinus radiata in south-central Chile, using the simulated presence of conspecifics as a potential tool to attract rayaditos to new available sites to nest. We simulated the presence of conspecifics through playback during 45 days prior nest building. Our results showed two contrasting outcomes. Firstly, conspecific simulation attracts rayaditos, by increasing their density before playback experiments by 75%. Secondly, rayaditos tended to avoid playback treatment sites as nesting started. The establishment of nests occurred 71% of the time and started 20 days earlier in control sites compared to playback treatment. Other secondary cavity-nesting birds, such as the House Wren (Troglodytes aedon; Troglodytidae) and White-throated Treerunner (Pygarrhichas albogularis; Furnariidae), also avoided playback plots as nesting sites. The scarcity of cavities in pine plantations may increase the aggressive defense of breeding territories, making cavity-nesting birds move to other previously known vacant sites to nest when they listen other birds in the nesting site. It is highly recommended to assess the behavioral response to conspecific and heterospecific birds before the establishment of a management measure aiming to attract or discourage the presence of a target species.
Abstract & References : Full Text : PDF (1026 KB)


Moonlight-related mortality: lunar conditions and roadkill occurrence in the Amami Woodcock Scolopax mira Full Access

Taku Mizuta
pg(s) 544–552
Abstract
Roadkill is one of the most striking ecological problems related to roads and traffic. The Amami Woodcock, Scolopax mira, an endemic and endangered species on the islands of southwestern Japan, ventures out on roads at night, making it susceptible to becoming roadkill. In the present study, I investigated woodcock behavior on roads at night, trends in nighttime traffic at roadkill hotspots, and dates when roadkill occurred in the past on Amami-Oshima Island in southwestern Japan, to develop mitigation measures to prevent roadkill in this species. Woodcocks were abundant on roads when the moon was waxing; ∼90% of nighttime traffic was recorded between dusk and midnight. These findings were consistent with the occurrence pattern of roadkill in the past, that is, roadkills occurred frequently during the first half of the synodic month when the waxing moon crosses the meridian from dusk until midnight. This pattern was obvious particularly in the breeding season (Feb–May). As a mitigation measure, drivers should be asked to reduce their vehicle speed on moonlit nights, particularly several days before the full moon in March, because this is the most vulnerable period for the Amami Woodcock. The present study revealed that the interplay of three factors (woodcock behavior, trends in nighttime driving, and lunar conditions) accounts for the seasonal, periodic, and temporal patterns of roadkill specific to this species. Because night activities of various animals are affected by phases of the moon, lunar conditions may have stronger effects on roadkill in a wider variety of animals than has been previously recognized. Taking lunar conditions into consideration would be important for better understanding of roadkill patterns in a wide variety of animals using roads at night.


Sexual dimorphism and body condition of wintering White-rumped Sandpipers in southern Brazil Full Access

Angelo L. Scherer, Janete F. M. Scherer, Maria V. Petry, and Victor H. Valiati
pg(s) 553–561
Abstract
We used discriminant function analysis (DFA) of a series of external morphometric measurements, with confirmation by genetic methods, to develop a simple method to determine the sex of adult White-rumped Sandpipers (Calidris fuscicollis) wintering in southern Brazil. In total, we evaluated the sexual size dimorphism (SSD) of 82 males and 102 females captured with mist nets during the non-breeding period from 2010–2012 using eight morphological measurements. We found significant sex differences: females are significantly larger than males in bill and total head and wing lengths (% SSD 1.0–6.2%). The SSD in skull and bill lengths showed a tendency to maximize the bill length in females, while males exhibited a greater skull length than females (2.6%). Both males and females showed similar body mass, and heavier birds were found in the fall before the northward migration. Body condition showed no difference between the sexes but was higher in the fall than the spring. Molecular sexing showed that DFA would lead to misclassification of sex. Given this, the use of morphological measurements for sexing non-breeding birds of this species in the wintering area should be avoided.



SHORT COMMUNICATIONS


First Record of Hybridization in the Hawaiian Honeycreepers: 'I'iwi (Vestiaria coccinea) × 'Apapane (Himatione sanguinea) Full Access

Jessie L. Knowlton, David J. Flaspohler, N. C. Rotzel Mcinerney, and Robert C. Fleischer
pg(s) 562–568
Abstract
The adaptive radiation of the Hawaiian honeycreepers is the largest ever recorded for birds on an oceanic archipelago. Despite including >50 species in 21 genera, no hybridizations across honeycreeper species have ever been confirmed. Here, we report genetic and morphological analyses that verify the first hybrid between two Hawaiian honeycreeper species: the 'I'iwi (Vestiaria coccinea) and 'Apapane (Himatione sanguinea). This hybridization is notable given that the parental species diverged ∼1.6 mya and show distinct morphological differences. Further, this discovery is important in light of recent evidence that hybridization plays an important role in speciation and genetic diversity in both plants and animals.
Abstract & References : Full Text : PDF (4583 KB)


Age-Ratios and Condition of En Route Migrant Blackpoll Warblers in the British Virgin Islands Full Access

Clint W. Boal
pg(s) 568–574
Abstract
The en route migration ecology of Blackpoll Warblers (Setophaga striata) is poorly understood, yet intriguing. Blackpoll Warblers undertake the longest open water migration of any wood warbler species, traveling from northeastern North America to South America, with the first potential landfall being the West Indies. This migration requires substantial energy reserves and subjects Blackpoll Warblers to unpredictable weather events, which may influence survival. Few studies have examined age ratios or condition of Blackpoll Warblers while the warblers are en route through the Caribbean region. I captured and banded Blackpoll Warblers in the British Virgin Islands over 10 consecutive autumn migrations. Ratios of hatch-year to adult Blackpoll Warblers were variable but averaged lower than the ratios reported at continental departure locations. Average mass of Blackpoll Warblers was less than that reported at continental departure locations, with 26% of adults and 40% of hatch-year birds below the estimated fat free mass; hatch-year birds were consistently in poorer condition than adults. Blackpoll Warblers captured in the British Virgin Islands were also in poorer condition than those reported from the Dominican Republic and Barbados; this may be because of the British Virgin Islands being the first landfall after the transatlantic crossing, whereas Blackpoll Warblers arriving at the other Caribbean study locations may have had opportunities for stopover prior to arrival or have departed from farther south on the continent. However, this suggests that the British Virgin Islands likely provide important stopover habitat as a first landfall location for Blackpoll Warblers arriving from the transatlantic migration route.


Sex and Age Group Specific Changes in Body Condition of Red-tailed Hawks in Central Nebraska Full Access

Casey W. Schoenebeck, Matthew Turco, Rae M. Fahrlander, Kaitlyn M. Darveau, and Thomas L. Freeman
pg(s) 575–580
Abstract
The central plains and the Platte River Valley of Nebraska are recognized as important winter habitat for many raptor species, but few studies have evaluated the ecology or physiology of birds of prey wintering in the region. The purpose of our study was to collect morphological data from Red-tailed Hawks (Buteo jamaicensis) occupying the study area during non-breeding months to better understand the sex ratios and potential changes in body condition of raptors in central Nebraska. Female Red-tailed Hawks were trapped significantly more often than males (χ2  =  11.560, df  =  1, P < 0.01), and data suggest that the population consists of a larger number of adult females followed by juvenile females and adult males, respectively. No juvenile males were captured during the study. Stratifying the data by sex and age group indicate that adult female Red-tailed Hawks significantly increase body mass (F  =  13.049, df  =  1, 13, P  =  0.004) over time, and normalization of data by animal size to form a body condition index suggests the increase in mass resulted from the accumulation of energy reserves. Juvenile female and adult male mass did not significantly change with time during the study. We propose that these data support adult females occupying the study area at higher frequencies than males or other age groups, and that the region may be important to adult females for accumulating energy reserves to meet the challenges of the upcoming reproductive cycle.


Plumage Coverage is Related to Body Condition and Ectoparasitism in Blue-black Grassquits Full Access

Rodrigo B. Magalhães, Pedro Diniz, and Regina H. Macedo
pg(s) 581–584
Abstract
Females may prefer elaborate sexual ornaments in males as these can be costly and may honestly indicate male viability. We used a wild population of the Blue-black Grassquit (Volatinia jacarina) in central Brazil to test whether more ornamented males have lower parasite loads (parasite-mediated sexual selection) and/or better body condition (condition-dependent sexual selection) compared with less ornamented males. We predicted that blue-black plumage coverage should be positively correlated to body condition (weight/tarsus) and negatively correlated to parasite load (Mallophaga lice). We found that blue-black plumage coverage of grassquit males was positively related to body condition score and negatively related to ectoparasite load. However, body condition was not correlated with ectoparasite load in these males. Our data are consistent with the hypothesis of sexual selection mediated by parasites as well as with the hypothesis of sexual selection mediated by body condition, indicating that nuptial plumage coverage can be an honest signal of male quality in Blue-black Grassquits, and could thus be used by females during mate choice.


Factors Influencing Mortality of Eared Grebes (Podiceps nigricollis) during a Mass Downing Full Access

Anthony J. Roberts, Michael R. Conover, and Jonathan L. Fusaro
pg(s) 584–591
Abstract
During the fall, hundreds of thousands of Eared Grebes (Podiceps nigricollis) stage on the Great Salt Lake, Utah. Mortalities resulting from birds being forced to the ground (downings) during migration occur every few years. A large (>7,000 birds) die-off of migrating Eared Grebes occurred 12 December 2011 in and around Cedar City, Utah. We examined body condition, age, sex, and heavy metal concentrations among downed birds and those that still occupied the Great Salt Lake both pre- and post-downing. Eared Grebes that we collected pre-downing were heavier (523 g) than deceased birds (433 g). Body weight (g) and subcutaneous fat thickness (mm) were lower in downed birds than pre-downing birds, likely the result of the 400-km flight from the staging area to Cedar City. Liver, heart, and intestine weights were all significantly greater in both pre- and post-downing birds than downed birds. This may be because of tissue catabolism during flight or incomplete physiological changes before migration. Adult biased age ratios were observed in all groups but pre-downing (34 adults: 5 juveniles) and post-downing (39: 2) groups were less biased than the downed group (100∶ 1). Mercury and selenium wet weight concentrations in all groups were above the level observed to impact some birds' reproduction and locomotion. Mercury concentrations in the liver ranged from 4.4–25.8 ppm wet weight and mercury concentrations measured in birds collected pre- and post-downing were lower than downed birds. Despite high levels of mercury and selenium, no adverse effects of heavy metal contamination have been noted in studies of Eared Grebes on the Great Salt Lake. Weather was likely the proximate cause of the downing, but impacts of heavy metal toxicity should be examined further to determine their effect on migrating Eared Grebes.


Habitat Selection by White Storks Breeding in a Mosaic Agricultural Landscape of Central Poland Full Access

Tomasz Janiszewski, Piotr Minias, Zbigniew Wojciechowski, and Patrycja Podlaszczuk
pg(s) 591–599
Abstract
The number of White Storks (Ciconia ciconia) has been decreasing in many parts of Europe at least since the middle of the 20th century. Intensification of agriculture and continuous conversion of natural habitats, such as wetlands, into agricultural landscapes have been recognized as the most important determinants of dramatic reductions in population sizes of this species. For this reason, providing quantitative estimates of habitat requirements may allow us to identify the key biota which should be prioritized for conservation. The aim of this study was to investigate White Storks' habitat selection in a mosaic agricultural landscape in central Poland. We found that territories associated with large river valleys were highly preferred by first-arriving storks. We also recorded lower intensity of brood reduction and higher reproductive success of storks breeding in such territories. Thus, it seems likely that location of nests close to river valleys provided easy access to rich food resources associated with wetlands. In fact, distance to nearest wetland was the second strongest predictor of nest-site selection in the studied population. We also demonstrated that pairs nesting in the territories with a high proportion of wetlands showed lower levels of brood reduction in comparison to pairs having poorer access to wet habitat patches. Finally, we found that although early arriving storks avoided settling in an urbanized landscape, they selected nesting sites located close to buildings. The results of this study confirmed high importance of wet grasslands for the core central European population of White Storks.


No Sex Bias in Wood Thrushes (Hylocichla mustelina) Captured by Using Audio Playback during the Non-breeding Season Full Access

Sean Chin, E. A. McKinnon, Kevin C. Fraser, Jamie Rotenberg, and B. J. M. Stutchbury
pg(s) 599–605
Abstract
Conservation of migratory songbird species requires information on abundance and survival over the annual cycle, including from overwintering sites. Broadcasting recorded calls or songs (playback) often increases detections or capture rates of birds, and can improve estimates of abundance or survival. Wood Thrushes overwintering in Belize regularly respond to broadcasted conspecific vocalizations (songs); however, it is unknown if song attracts a specific age, sex, or size class of birds. Our goal was to determine if the use of playback resulted in sex, age, or size-biases in captures of Wood Thrushes, relative to captures without playback, at a non-breeding site in Belize, Central America. We predicted that birds responding to playback would be: (1) male, (2) adults, and (3) larger than birds caught without playback, owing to social dominance of larger adult males over juveniles and females. Surprisingly, we found no significant difference in sex or age ratio, or body size of birds captured with or without playback. It may be that predicted patterns of social dominance are not apparent in non-breeding Wood Thrushes, or that song playback does not elicit responses related to local social dominance. Regardless of the mechanism, we conclude that the use of song playback during the non-breeding season does not bias captures of Wood Thrushes by sex, age, or body size, and when used with caution, can be an effective tool for studies on the species' wintering grounds.


Male Dark-eyed Juncos (Junco hyemalis) Respond Differentially to Playback of Local and Foreign Song Full Access

Dustin G. Reichard
pg(s) 605–611
Abstract
The songs of oscine birds, given their cultural inheritance, can readily diverge, which can foster assortative mating and ultimately reproductive isolation. The species complex of Dark-eyed Juncos (Junco hyemalis) consists of at least six distinct subspecies and represents an ideal system for studying divergence in mating signals owing to its recent, rapid radiation throughout North America since the last glaciation (<15,000 yrs). Each subspecies of Dark-eyed Junco is characterized by distinct plumage and morphological characteristics, but divergence among the subspecies in song and the role of song as a potential isolating mechanism remains to be rigorously tested. In this study, I compared territorial responses of male juncos in Virginia to playback of locally recorded songs and songs recorded from a different population and subspecies in California. Males responded aggressively to playbacks from both populations, but they approached more rapidly and closely, and performed more flyovers when responding to local song types. While these results suggest that male juncos can discriminate between songs of different populations, future work should investigate female preferences for local and foreign songs and also address more populations, particularly those located in active hybrid zones.


First Observations of Termite Insectivory in the Bateleur (Terathopius ecaudatus) Full Access

Natasha D. G. Hagemeyer and Monica L. Bond
pg(s) 611–613
Abstract
Bateleurs (Terathopius ecaudatus), Steppe Eagles (Aquila nipalensis), and Tawny Eagles (Aquila rapax) were observed consuming termites during a termite emergence on 30 December 2012 in Mkomazi National Park and on 20 May 2013 in Tarangire National Park, Tanzania. This behavior is well known in Steppe and Tawny eagles, but these are the first records of Bateleurs using termites as a food source.



ORNITHOLOGICAL LITERATURE


Ornithological Literature Full Access

John Faaborg, Book Review Editor
pg(s) 614–620
    Citation : Full Text : PDF (76 KB)

    The Weaver's Apprentice Full Access

    Edward H. Burtt, Jr
    pg(s) 621–621
    Citation : Full Text : PDF (25 KB)

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