bluuebunny/crossref_metadata_2025 huggingface dataset:
Further Evidence for Paraphyly of the Formicariidae (Passeriformes)
Authors: Rice Nathan H.
Published: September 2019

The historical relationships of ground antbirds and their relatives have long been unresolved. Here, I present a phylogenetic analysis of ground antbird (Formicariidae) relationships based on DNA sequence data from the cytochrome-b and ND2 genes. Results support novel hypotheses of historical relationships, including two revisions of suboscine taxonomy: (1) paraphyly of the Formicariidae with the tentative inclusion of at least some rhinocryptids (Liosceles, Rhinocrypta, and Scytalopus) in the ground antbird lineage, and (2) placement of Pittasoma with Conopophaga in the Conopophagidae.
Age-Based Plumage Changes in the Lance-Tailed Manakin: A Two-Year Delay in Plumage Maturation
Authors: DuVal Emily H.
Published: September 2019

I investigated the relationship of plumage to age and sex in the Lance-tailed Manakin (Pipridae, Chiroxiphia lanceolata) in the lowlands of western Panama from 1999–2004. I captured birds in mist nets, categorized their plumages, examined them for molt, and followed them for several years to document plumage changes. Male Lance-tailed Manakins exhibited three distinct postjuvenal plumages. Males achieved definitive adult plumage through sequential changes that occurred in the same order as in other Chiroxiphia manakins. Definitive male plumage developed over the same time span as reported for C. caudata but one year faster than C. linearis. Juvenal male plumage was similar to that of females, and 5% of 226 females had plumage similar to formative male plumage. Genetic sexing verified that changes observed late in the formative male plumage unambiguously identified sex and age of individual birds. This information can be used in behavioral studies to identify the age of male Lance-tailed Manakins captured in any of the predefinitive plumage stages.
Intraclutch Egg-Size Variation in Magellanic Penguins
Authors: Rafferty Nicole E. , Boersma P. Dee , Rebstock Ginger A.
Published: September 2019

We investigated patterns and consequences of intraclutch egg-size variation in Magellanic Penguins (Spheniscus magellanicus). First-laid eggs were significantly larger than second-laid eggs, although the mean difference represented only 2% of an average egg's volume. The degree of intraclutch egg-size variation was similar among years and females of different ages. Intraclutch egg-size variation did not affect intraclutch differences in chick hatching weights or fledging success. We found no selective advantage for laying eggs of different sizes. Because both eggs have an equal probability of being lost, chance favors equal provisioning of eggs. Egg volume explained 35% of the variation in hatching weight but did not determine fledging success. Laying order, year, and female age were better predictors of fledging success than egg size. Factors such as laying and hatching order, parental quality, oceanographic conditions, fights, and predation are more important in determining chick survival than are differences in egg size.
Group Living in the Black-Breasted Wood-Quail and the Use of Playbacks as a Survey Technique
Authors: Hale Amanda M.
Published: September 2019

I used playbacks of recorded group song to survey and capture Black-breasted Wood-Quail (Odontophorus leucolaemus), a cloud forest endemic, in Monteverde, Costa Rica. This species is abundant in the dense understory of large windbreaks, forest fragments, and continuous forest of the Monteverde Reserve Complex. Mean covey size was four adults (range = 2–9 adults) and mean density, which did not differ between fragmented and continuous forest, was one covey per 3.3 ha. Wood-Quail defended all-purpose group territories and coveys persisted from one year to the next, indicating a group structure that is very different from what is found in most New World quail. A peak in breeding activity occurred at the transition from the wet to the dry season and larger groups produced significantly more juveniles than smaller groups in this population. Playbacks were a useful technique for detecting Black-breasted Wood-Quail; coveys responded to 65% of survey attempts by chorus and approach. By repeating the survey just three times, I was able to detect 91% ± 5% of all coveys that were known from extensive searches to occur in the remnant forest patches of the Monteverde community. The year-round sociality that is seen in this species is due in part to the retention of young on the natal territory beyond the age of sexual maturity. The intriguing relationship between group size and reproductive success in this population suggests the wood-quail may provide the first demonstration of a cooperative breeding system in the Galliformes.
A Hierarchical Model for Regional Analysis of Population Change Using Christmas Bird Count Data, with Application to the American Black Duck
Authors: Link William A. , Sauer John R. , Niven Daniel K.
Published: September 2019

Analysis of Christmas Bird Count (CBC) data is complicated by the need to account for variation in effort on counts and to provide summaries over large geographic regions. We describe a hierarchical model for analysis of population change using CBC data that addresses these needs. The effect of effort is modeled parametrically, with parameter values varying among strata as identically distributed random effects. Year and site effects are modeled hierarchically, accommodating large regional variation in number of samples and precision of estimates. The resulting model is complex, but a Bayesian analysis can be conducted using Markov chain Monte Carlo techniques. We analyze CBC data for American Black Ducks (Anas rubripes), a species of considerable management interest that has historically been monitored using winter surveys. Over the interval 1966–2003, Black Duck populations showed distinct regional patterns of population change. The patterns shown by CBC data are similar to those shown by the Midwinter Waterfowl Inventory for the United States.
A Possible Role for Red Squirrels in Structuring Breeding Bird Communities in Lodgepole Pine Forests
Authors: Siepielski Adam M.
Published: September 2019

Nest predation is thought to play an important role in structuring certain breeding bird communities. One potential consequence of nest predation is lower recruitment in breeding birds, which may be manifested as lower breeding bird abundance. Lodgepole pine (Pinus contorta ssp. latifolia) forests east and west of the Rocky Mountains became isolated following glacial retreat 12 000 years ago and differ in whether or not red squirrels (Tamiasciurus hudsonicus), which are a key nest predator, are present. Breeding bird abundance in lodgepole pine forests was compared between four ranges with red squirrels and four ranges without red squirrels. Species grouped into canopy and understory nesting guilds were, on average, two and three times more abundant, respectively, in forest ranges without red squirrels than in ranges with red squirrels; no statistically significant differences were found for midstory, ground, or cavity nesters. These results suggest that geographic variation in the presence or absence of red squirrels is likely important in structuring breeding bird communities in lodgepole pine forests across the landscape.
Predicting Regional Abundance of Rare Grassland Birds with a Hierarchical Spatial Count Model
Authors: Thogmartin Wayne E. , Knutson Melinda G. , Sauer John R.
Published: September 2019

Grassland birds are among the most imperiled groups of birds in North America. Unfortunately, little is known about the location of regional concentrations of these birds, thus regional or statewide conservation efforts may be inappropriately applied, reducing their effectiveness. We identified environmental covariates associated with the abundance of five grassland birds in the upper midwestern United States (Bobolink [Dolichonyx oryzivorus], Grasshopper Sparrow [Ammodramus savannarum], Henslow's Sparrow [A. henslowii], Sedge Wren [Cistothorus platensis], and Upland Sandpiper [Bartramia longicauda]) with a hierarchical spatial count model fitted with Markov chain Monte Carlo methods. Markov chain Monte Carlo methods are well suited to this task because they are able to incorporate effects associated with autocorrelated counts and nuisance effects associated with years and observers, and the resulting models can be used to map predicted abundance at a landscape scale. Environmental covariates were derived from five suites of variables: landscape composition, landscape configuration, terrain heterogeneity and physiognomy, climate, and human influence. The final models largely conformed to our a priori expectations. Bobolinks and Henslow's Sparrows were strongly sensitive to grassland patch area. All of the species except Henslow's Sparrows exhibited substantial negative relations with forest composition, often at multiple spatial scales. Climate was found to be important for all species, and was the most important factor influencing abundance of Grasshopper Sparrows. After mapping predicted abundance, we found no obvious correspondence in the regional patterns of the five species. Thus, no clearly defined areas exist within the upper midwestern United States where management plans can be developed for a whole suite of grassland birds. Instead, a larger, region-wide initiative setting different goals for different species is recommended.
Cross-scale Correlations and the Design and Analysis of Avian Habitat Selection Studies
Authors: Battin James , Lawler Joshua J.
Published: September 2019

It has long been suggested that birds select habitat hierarchically, progressing from coarser to finer spatial scales. This hypothesis, in conjunction with the realization that many organisms likely respond to environmental patterns at multiple spatial scales, has led to a large number of avian habitat studies that have attempted to quantify habitat associations at multiple scales. Typically, multiscale habitat selection studies involve the assessment of habitat selection separately at two or more scales. Until recently, these studies have ignored the potential for cross-scale correlations: correlations among habitat variables across scales. If environmental patterns are correlated across the scales being analyzed, researchers using traditional analytical methods may reach erroneous conclusions about the presence or strength of habitat associations at a given scale. We discuss the ways in which cross-scale correlations manifest themselves in two types of habitat selection studies: (1) “constrained” designs that assume a hierarchical ordering of habitat selection decisions, and (2) “unconstrained” designs, which do not assume such a selection process. We demonstrate approaches for quantifying and modeling cross-scale correlations, including a simulation model, a variance decomposition technique, and a hierarchical modeling approach based on classification tree analysis. We conclude that cross-scale correlations have the potential to affect data interpretation in all types of habitat selection studies and that, even with careful attention to experimental design and the application of newly developed statistical techniques, it is likely their effects cannot be eliminated.
Breeding Dispersal In the California Spotted Owl
Authors: Blakesley Jennifer A. , Anderson David R. , Noon Barry R.
Published: September 2019

Spotted Owls (Strix occidentalis) are territorial, generally nonmigratory, and strongly philopatric. Nevertheless, California Spotted Owls (S. o. occidentalis) exhibited breeding dispersal during 7% of interannual observations of banded individuals (n = 54 of 743 occasions). Based on ecological theory and published literature, we made a priori predictions about the factors associated with the probability of breeding dispersal and breeding dispersal distance, and about the consequences of dispersal. Breeding dispersal probability was higher for younger owls, single owls, paired owls that lost their mates, owls at lower quality sites, and owls that failed to reproduce in the year preceding dispersal. Sex had little effect on the probability of breeding dispersal. Dispersal distance was similar for female and male owls (median = 7 km, range = 1–33 km). We found no strong relationships between dispersal distance and any of the conditions that were associated with the probability of breeding dispersal. Dispersal resulted in improved territory quality in 72% of cases. These results indicate that breeding dispersal was condition-dependent and adaptive.
Annual Variation in Numbers of Breeding California Gulls at Mono Lake, California: the Importance of Natal Philopatry and Local and Regional Conditions
Authors: Wrege Peter H. , David Shuford W. , Winkler David W. , Jellison Robert
Published: September 2019

The California Gull (Larus californicus) breeding colony at Mono Lake, California, is the second largest in the world, but its size can fluctuate annually by >45%. We examined six groups of factors that potentially could affect the numbers of pairs nesting each year, including availability of nesting habitat, numbers of potential breeding gulls, environmental conditions along the Pacific coast in the preceding winter, spring conditions at the lake, food availability at the lake, and prior breeding experience. Four variables explained >80% of the variation in the numbers of breeding gulls at Mono Lake between 1987 and 2003: the potential number of four-year-old gulls returning to the lake to breed for the first time, winter coastal conditions associated with the Pacific Decadal Oscillation, density of endemic brine shrimp (Artemia monica) close to the time of egg-laying, and mean temperature in the month before egg-laying. Of the four factors the latter two, which reflect local conditions near the time of egg-laying, had the most profound direct effect on the numbers of breeding gulls. Yearly variation in the snow pack and spring runoff affects brine shrimp numbers through changes in limnological conditions, thus regional climate patterns may indirectly influence gull numbers.
Influence of Habitat Heterogeneity on Distribution, Occupancy Patterns, and Productivity of Breeding Peregrine Falcons in Central West Greenland
Authors: Wightman Catherine S. , Fuller Mark R.
Published: September 2019

We used occupancy and productivity data collected at 67 cliffs used for nesting from 1972 to 1999 to assess patterns of distribution and nest-site selection in an increasing population of Peregrine Falcons (Falco peregrinus) in central West Greenland. Peregrine Falcons breeding at traditionally occupied cliffs used for nesting had significantly lower variation in productivity and thus these cliffs were better quality sites. This indicates that Peregrine Falcons occupied cliffs according to a pattern of despotic distribution. Falcons breeding at cliffs that were consistently occupied during the breeding season had higher average productivity and lower variation in productivity than falcons at inconsistently occupied cliffs, and thus consistent occupancy also was indicative of cliff quality. Features of high quality habitat included tall cliffs, greater change in elevation from the lowest point within 3 km of the cliff to the cliff top (elevation gain), and protection from weather on the eyrie ledge. Spacing of suitable and occupied cliffs also was an important feature, and the best cliffs generally were more isolated. Increased spacing was likely a mechanism for reducing intraspecific competition. Our results suggest that Peregrine Falcons use a resource defense strategy to compete for better quality habitats and may use spacing and physical features of a nest site to identify good quality breeding habitat.
An Assessment of Bird Habitat Quality Using Population Growth Rates
Authors: Knutson Melinda G. , Hines Randy K. , Powell Larkin A. , Friberg Mary A. , Niemi Gerald J.
Published: September 2019

Survival and reproduction directly affect population growth rate (λ), making λ a fundamental parameter for assessing habitat quality. We used field data, literature review, and a computer simulation to predict annual productivity and λ for several species of landbirds breeding in floodplain and upland forests in the Midwestern United States. We monitored 1735 nests of 27 species; 760 nests were in the uplands and 975 were in the floodplain. Each type of forest habitat (upland and floodplain) was a source habitat for some species. Despite a relatively low proportion of regional forest cover, the majority of species had stable or increasing populations in all or some habitats, including six species of conservation concern. In our search for a simple analog for λ, we found that only adult apparent survival, juvenile survival, and annual productivity were correlated with λ; daily nest survival and relative abundance estimated from point counts were not. Survival and annual productivity are among the most costly demographic parameters to measure and there does not seem to be a low-cost alternative. In addition, our literature search revealed that the demographic parameters needed to model annual productivity and λ were unavailable for several species. More collective effort across North America is needed to fill the gaps in our knowledge of demographic parameters necessary to model both annual productivity and λ. Managers can use habitat-specific predictions of annual productivity to compare habitat quality among species and habitats for purposes of evaluating management plans.
Abundance and Productivity of Warbling Vireos Across an Elevational Gradient in the Sierra Nevada
Authors: Purcell Kathryn L.
Published: September 2019

Recent studies have shown that Warbling Vireos (Vireo gilvus) are declining in California and that these trends are due to low reproductive success. Brood parasitism by Brown-headed Cowbirds (Molothrus ater) has been implicated in the low productivity. I explored two hypotheses related to population dynamics of Warbling Vireos along an elevational gradient: (1) potential source populations exist at high elevations where cowbirds are rare, and (2) potential source populations occur in the center of the elevational distribution with less productive populations at upper and lower elevations. From 1985 through 2002 I studied the abundance and productivity of Warbling Vireos over an elevational gradient in the southern Sierra Nevada. Warbling Vireos were most abundant in mid elevation mixed conifer sites, less abundant in lower elevation ponderosa pine sites and upper elevation true fir sites, and rare in upper elevation lodgepole pine sites. Likewise, daily survival rates of nests were highest at mid elevations (1800 m) and gradually decreased at both higher and lower elevations. Compared to other populations studied in California, nest success in mixed conifer habitat was high (60%, n  =  58). Although rates of brood parasitism were high enough to be of concern in low-elevation ponderosa pine forests, cowbird parasitism was not observed in mid- to upper-elevation forests. Warbling Vireos were most productive where they were most abundant. The hypothesis that potential source populations exist at upper elevations did not appear to hold at the upper bounds of the elevational distribution. The results of this study provide support for the hypothesis that potential source populations occur in the center of the elevational distribution, with less productive populations at both lower and higher elevations.
The Duet Code of the Female Black-Bellied Wren
Authors: Logue David M.
Published: September 2019

In many duet-singing songbirds, paired birds combine their song types nonrandomly to form duet songs. Several different behavioral mechanisms could generate nonrandom song type associations in duets. I tested female Black-bellied Wrens (Thryothorus fasciatoventris) for one such mechanism: adherence to a set of rules linking female response songs to male stimulus songs. I call this set of rules a “duet code.” Duets of free-living Black-bellied Wrens were recorded in 2001 and 2002. In 2003 I returned to the same territories and played the male song types from the recorded duets. Females answered male song stimuli as if duetting with the playback speaker. Although the known repertoires of females averaged 8.4 song types, each female sang only a single song type in response to each male song type. Random answering could not account for this pattern, supporting the hypothesis that females abide by duet codes. Females that were still paired with their mates from 2001–2002 answered 100% of their mate's songs with the same song types they had used previously, demonstrating that codes are stable over time. In contrast, females that were new to a territory answered an average of only 18% of their mate's song types with the same song type as the previous female, indicating that duet codes are individually distinctive. Duet participation by female Black-bellied Wrens represents a special kind of animal communication, in which discrete vocal signals consistently elicit discrete vocal responses according to an individually distinctive set of rules.
Singing of Hermit Warblers: Dialects of Type I Songs
Authors: Janes Stewart W. , Ryker Lee
Published: September 2019

Hermit Warblers (Dendroica occidentalis) sing distinct dialects of type I songs, the most common song before pairing. Eight dialects were identified and described in a 22 900 km2 area in southwestern Oregon and northern California. The dialects were well defined geographically with contact areas between dialects seldom extending more than 6 km. Gaps in forested habitat of ≥10 km separated several dialects, but within forested areas dialect boundaries did not conform to obvious habitat, elevation, or geographic boundaries. Few songs containing syllables or phrases from more than one dialect were identified, and birds incorporating elements from two different dialects inhabited areas close to the common boundary between the two. Multivariate analysis showed that birds in neighboring areas had dialects most similar in structure, but a more complex history of dialect development or origin is suggested in other areas.
Long and Short Trips in Nonbreeding Buller's Albatrosses: Relationships with Colony Attendance and Body Mass
Authors: Stahl Jean-Claude , Sagar Paul M.
Published: September 2019

Foraging strategies of nonbreeding seabirds attending colonies remain virtually unknown. Here we report the results of a satellite telemetry study of nonbreeding Buller's Albatrosses (Thalassarche bulleri) from the Snares island group south of New Zealand in 2000–2001. Two 6- to 7-year-old prebreeding birds dispersed to Tasmania, Australia, from late May until at least late July. Six older birds (five prebreeding birds, one former breeding adult) all adopted a dual strategy of short trips (mean duration 1.3 days, mean foraging range 129 km) and long trips to southern New Zealand (9.6 days, 871 km) or Tasmania (22.0 days, 1918 km). Time allocation to short trips increased with age and experience (both sexes) and nest-site attendance (males), and decreased during the guard (when the chick is attended) and late postguard (chick left unattended) stages (females). Up to the guard stage, most birds present at their colony on consecutive days foraged overnight (mean foraging range 101 km). Nonbreeding birds used the same foraging areas as breeding adults, but allocated more foraging time to short trips during the corresponding incubation period and early postguard stage, and to long trips during the guard stage. Results suggest that prebreeding birds explore foraging areas sequentially, and increase their time ashore by progressing from making only long trips, to introducing short overnight trips, to modifying the duration of and allocation between long and short trips. Changes in body mass recorded on Solander Island (160 km north of the Snares) show that experienced nonbreeding birds initiate long foraging trips to regain mass lost during short trips, and suggest that less frequent short trips (and hence fewer returns ashore) among inexperienced birds are related to less efficient foraging during long trips.
Intercolony and Annual Differences in the Diet and Feeding Ecology of Little Tern Adults and Chicks in Portugal
Authors: Catry Teresa , Ramos Jaime A. , Paiva Vitor H. , Martins Jorge , Almeida Ana , Palma Jorge , Andrade Pedro J. , Peste Filipa , Trigo Sandra , LuÍs António
Published: September 2019

We used pellets and prey dropped near nests to study the diet and feeding ecology of Little Tern (Sterna albifrons) adults and chicks in northern and southern Portugal during 2000–2004. We compared diets among study areas, years, and birds breeding in two main habitat types: sandy beaches and salinas (man-made salt-pans). We also sampled prey fish in one study area and used published data from another area to examine whether the diet of Little Tern adults and chicks corresponded with the abundance of prey found in primary foraging habitats. Adult Little Terns fed mainly on sand-smelts (Atherina spp.) and gobies (Pomatoschistus spp.), which were the most abundant fish species in our estuarine and lagoon study areas. Despite some differences among colonies we did not find clear differences in adult diets among study areas and habitat types. Little Tern chicks also ate primarily Atherina spp., but their diet was more diverse than that of the adults, and characterized by a significantly higher proportion of prey with a high energetic value such as sardines (Sardina pilchardus), garfish (Belone belone), and killifish (Fundulus spp.). Chick diets differed significantly between habitat types, which may be a consequence of the limited foraging range of adult breeding birds. Both adult and chick diets matched the abundance of the main prey in our study areas, confirming the opportunistic foraging character of this species. We suggest that annual variation in prey availability may be the most important factor explaining annual variation in adult diets.
Tests of Ecological, Phenotypic, and Genetic Correlates of Extra-Pair Paternity in the House Sparrow
Authors: Stewart Ian R. K. , Hanschu Richard D. , Burke Terry , Westneat David F.
Published: September 2019

We performed a two-year study of extra-pair paternity in the House Sparrow (Passer domesticus) to test a suite of hypotheses relating to ecological factors associated with breeding conditions and parental phenotypes and genotypes. Extra-pair fertilizations (EPFs) accounted for 45 of 419 (11%) nestlings and occurred in 33 of 126 (26%) broods. EPFs were not correlated with breeding synchrony or breeding density, although they were significantly more common toward the end of each breeding season. Body size and the size of the bib, a secondary sexual character, were no different between males that were cuckolded and those that achieved full paternity in their nests. Older males were cuckolded as frequently as yearlings, and there was no difference between males that were cuckolded and those that were not with regard to two measures of individual genetic diversity. There was no evidence that females sought EPFs to avoid inbreeding, since EPFs were equally likely to be present among pairs that were closely related and those that were only distantly related, and females were equally related to their extra-pair mates as they were to their within-pair mates. Furthermore, extra-pair sires did not possess alleles that were rare in the population. In sum, despite a substantial sample size, we found few correlates of extra-pair paternity in House Sparrows.
Colony Mapping: A New Technique for Monitoring Crevice-Nesting Seabirds
Authors: Renner Heather M. , Renner Martin , Reynolds Joel H. , Harding Ann M. A. , Jones Ian L. , Irons David B. , Byrd G. Vernon
Published: September 2019

Monitoring populations of auklets and other crevice-nesting seabirds remains problematic, although numerous methods have been attempted since the mid-1960s. Anecdotal evidence suggests several large auklet colonies have recently decreased in both abundance and extent, concurrently with vegetation encroachment and succession. Quantifying changes in the geographical extent of auklet colonies may be a useful alternative to monitoring population size directly. We propose a standardized method for colony mapping using a randomized systematic grid survey with two components: a simple presence/absence survey and an auklet evidence density survey. A quantitative auklet evidence density index was derived from the frequency of droppings and feathers. This new method was used to map the colony on St. George Island in the southeastern Bering Sea and results were compared to previous colony mapping efforts. Auklet presence was detected in 62 of 201 grid cells (each grid cell  =  2500 m2) by sampling a randomly placed 16 m2 plot in each cell; estimated colony area  =  155 000 m2. The auklet evidence density index varied by two orders of magnitude across the colony and was strongly correlated with means of replicated counts of birds socializing on the colony surface. Quantitatively mapping all large auklet colonies is logistically feasible using this method and would provide an important baseline for monitoring colony status. Regularly monitoring select colonies using this method may be the best means of detecting changes in distribution and population size of crevice-nesting seabirds.
Variation of West Nile Virus Antibody Prevalence in Migrating and Wintering Hawks in Central California
Authors: Hull Joshua , Ernest Holly , Hull Joshua , Hull Angus , Reisen William , Fang Ying , Ernest Holly
Published: September 2019

To assess the extent of West Nile virus (WNV) exposure of migrating (Marin Headlands) and wintering (Central Valley) hawks in California, plasma from 271 Red-tailed Hawks (Buteo jamaicensis), 19 Red-shouldered Hawks (B. lineatus), and 30 Cooper's Hawks (Accipiter cooperii) was tested for WNV antibodies during the winter of 2004–2005. WNV antibodies were found in 5% of migrating and 15% of wintering Red-tailed Hawks, 20% of migrating and 58% of wintering Red-shouldered Hawks, and 13% of migrating Cooper's Hawks. No individuals demonstrated visible signs of WNV illness. Red-tailed Hawks that tested positive for WNV antibodies displayed no difference from Red-tailed Hawks without WNV antibodies in weight to wing chord ratio or white blood cell counts. In the Central Valley, WNV antibodies were significantly more prevalent in Red-shouldered Hawks than in Red-tailed Hawks. Significantly more Red-tailed Hawks sampled on wintering grounds tested positive for WNV antibodies than Red-tailed Hawks sampled during migration.
Absence of Population Genetic Structure Among Breeding Colonies of the Waved Albatross
Authors: Huyvaert Kathryn P. , Parker Patricia G.
Published: September 2019

We used four variable microsatellite loci to examine the distribution of genetic variation and degree of genetic structuring among three subcolonies of Waved Albatrosses (Phoebastria irrorata). The breeding population of this species is almost entirely limited to the island of Española in the Galápagos Archipelago. Such strong philopatry could lead to population genetic structure among subcolonies on the island. Pairwise values of the FST analog, θ, calculated from microsatellite genotypes, were all less than 0.012, indicating little genetic differentiation and the presence of gene flow throughout the population.
First Evidence of Conspecific Brood Parasitism and Egg Ejection in Song Sparrows, With Comments on Methods Sufficient to Document These
Authors: Latif Quresh S. , Letitia Grenier J. , Heath Sacha K. , Ballard Grant , Hauber Mark E.
Published: September 2019

Conspecific brood parasitism occurs in many songbird species but has not been reported in Song Sparrows (Melospiza melodia). In three separate study areas where breeding Song Sparrows experience heavy nest predation pressure and Brown-headed Cowbird (Molothrus ater) parasitism, we observed six instances in which newly laid eggs were attributable to female Song Sparrows other than the nest owners. We also recorded the ejection of a sparrow egg from each of two videotaped nests. In a fourth study area without cowbird parasitism, genetic analysis of parentage revealed no conspecific brood parasitism. Given that egg ejection can accompany conspecific parasitism in Song Sparrows, we suggest that daily nest checks are insufficient to document the frequency of this tactic in some species in the absence of egg marking, videotaping, or genetic analyses. Since standard nest monitoring techniques may fail to detect conspecific brood parasitism, this behavior could be more prevalent than currently thought.
DNA Quality and Accuracy of Avian Malaria PCR Diagnostics: A Review
Authors: Freed Leonard A. , Cann Rebecca L.
Published: September 2019

Birds have become increasingly prominent in studies focusing on natural populations and their coevolved pathogens or examining populations under environmental stress from novel and emerging infectious diseases. For either type of study, new DNA-based diagnostic tests, using the polymerase chain reaction (PCR), present challenges in detecting the DNA of pathogens, which exist in low copy number compared with DNA of the host. One example comes from studies of avian malaria: conflicting claims are made by different laboratories about the accuracy of tests using various sets of primers and reagents, especially in relation to blood smears and immunological methods. There is little standardization of protocol or performance among laboratories conducting tests, in contrast to studies of human malaria. This review compares the problems of detecting avian malaria with those of detecting human malaria, and shows definitively that the buffer used to store blood samples following collection is associated with the accuracy of the test. Lower accuracy is associated with use of a lysis buffer, which apparently degrades the DNA in the blood sample and contributes to inhibition of PCR reactions. DNA extraction and purification techniques, and optimization of the PCR reaction, do not appear to be alternative explanations for the effect of storage buffer. Nevertheless, the purest DNA in standard concentrations for PCR is required so that different primers, DNA polymerases, and diagnostic tests can be objectively compared.
Demography, Genetics, and the Value of Mixed Messages
Authors: Pearce John M. , Talbot Sandra L.
Published: September 2019

Iverson et al. (2004) used estimates of the homing rate for molting adult Harlequin Ducks (Histrionicus histrionicus) in Alaska to draw inferences about population structure. Homing rates, defined as one minus the ratio of birds recaptured elsewhere to those recaptured at the original banding site, were high (0.95–1.00) for males and females. Iverson et al. (2004) concluded that these high rates of homing are indicative of demographic independence among molting groups separated by small distances (tens to hundreds of kilometers) and that conservation efforts should recognize this fine-scale population structure. We re-examined their use of the homing rate, because their assumption of equal detection probability across a wide sampling area could have led to an upward bias in their estimates of site fidelity. As a result, we are hesitant to agree with their conclusion of high adult homing to molting areas and that molt-site fidelity is evidence for demographic independence. Our hesitancy stems from the fact that little is known about juvenile and adult movements within and among years, breeding area origins, and the variation of demographic parameters (e.g., survival and productivity) among molting groups. Furthermore, population genetic data of these molting groups suggest gene flow at both nuclear and mitochondrial loci. Such mixed messages between demographic (i.e., banding) and genetic data are increasingly common in ornithological studies and offer unique opportunities to reassess predictions and make more robust inferences about population structure across broad temporal and spatial scales. Thus, we stress that it is this broader scale perspective, which combines both demography and genetics, that biologists should seek to quantify and conservation efforts should seek to recognize.
The Inflected Alarm Caw of the American Crow: Differences in Acoustic Structure Among Individuals and Sexes
Authors: Yorzinski Jessica L. , Vehrencamp Sandra L. , McGowan Kevin J. , Clark Anne B.
Published: September 2019

Previous research on individual differences in the acoustic structure of vocalizations and vocal recognition has largely focused on the contexts of parent-offspring interactions, territory defense, sexual interactions, and group cohesion. In contrast, few studies have examined individual differences in the acoustic structure of mobbing and alarm calls. The purpose of this study was to explore individual differences in the acoustic structure of the inflected alarm caw of the American Crow (Corvus brachyrhynchos). The alarm caws of 15 wild, marked individuals were recorded and 25 acoustic measurements were made automatically using customized software. A stepwise discriminant function analysis showed that 20 of the 25 variables were important in discriminating among individuals, with 65% classification success. We used factor analysis to reduce the large number of variables to a set of seven meaningful call features. All of these features differed among individuals, suggesting that American Crows have the potential to discriminate among individual birds on the basis of call structure alone. Five of the features differed between the sexes, with call frequency being the most significant. One clearly subordinate male clustered with the females, raising the possibility that social status partially determines the sex-based differences. Encoding of individual identity in alarm contexts may be adaptive if receiver vigilance and approach urgency depend on the status, reliability, or family membership of the alarm signaler.
Does Life History Predict Risk-Taking Behavior of Wintering Dabbling Ducks?
Authors: Ackerman Joshua T. , Eadie John M. , Moore Thomas G.
Published: September 2019

Life-history theory predicts that longer-lived, less fecund species should take fewer risks when exposed to predation than shorter-lived, more fecund species. We tested this prediction for seven species of dabbling ducks (Anas) by measuring the approach behavior (behavior of ducks when approaching potential landing sites) of 1099 duck flocks during 37 hunting trials and 491 flocks during 13 trials conducted immediately after the 1999–2000 waterfowl hunting season in California, USA. We also experimentally manipulated the attractiveness of the study site by using two decoy treatments: (1) traditional, stationary decoys only, and (2) traditional decoys in conjunction with a mechanical spinning-wing decoy. Approach behavior of ducks was strongly correlated with their life history. Minimum approach distance was negatively correlated with reproductive output during each decoy treatment and trial type. Similarly, the proportion of flocks taking risk (approaching landing sites to within 45 m) was positively correlated with reproductive output. We found similar patterns of approach behavior in relation to other life-history parameters (i.e., adult female body mass and annual adult female survival rate). Thus, species characterized by a slower life-history strategy (e.g., Northern Pintail [A. acuta]) were more risk-averse than species with a faster life-history strategy (e.g., Cinnamon Teal [A. cyanoptera]). Furthermore, although we were able to reduce risk-averseness using the spinning-wing decoy, we were unable to override the influence of life history on risk-taking behavior. Alternative explanations did not account for the observed correlation between approach behavior and life-history parameters. These results suggest that life history influences the risk-taking behavior of dabbling ducks and provide an explanation for the differential vulnerability of waterfowl to harvest.
Sex, Age, and Body Size Distributions of Western Sandpipers During the Nonbreeding Season With Respect to Local Habitat
Authors: Fernández Guillermo , Lank David B.
Published: September 2019

We documented the local density and sex, age-class, and body size distributions of Western Sandpipers (Calidris mauri) among habitats at Bahía Santa María, northwestern Mexico, during the nonbreeding season. Three habitats were recognized: brackish flats, mangroves, and cattail marshes, which we ranked as richest to poorest in food resources and safest to most dangerous in predation danger. Western Sandpiper population structure differed among habitats. Bird densities were highest in brackish flats, the richest and safest habitat, and males and adults of both sexes were overrepresented. In cattail marshes, which appeared to be the poorest and most dangerous habitat, bird densities were lower, and the sex ratio and age ratios within each sex were more even. In mangroves, bird densities were similar to those in cattail marshes, but sex and age ratios were similar to those in brackish flats. Exposed culmen, an index of structural size, was not related to habitat use in either sex. Body mass of immature males was more variable than that of adults among habitats and immature males gained mass throughout the winter. Birds in brackish flats and mangroves were initially heavier, but tended to lose mass, whereas birds in cattail marshes were initially lighter, but tended to gain mass. Mass distributions thus converged in late winter. While the social and ecological causes and significance of differential sex and age-class distributions among habitats remain largely unquantified, evidence from this and previous studies suggests that nonbreeding population structure is a common phenomenon with important implications for migratory shorebirds.
Polygyny and Extra-Pair Paternity in a Population of Southwestern Willow Flycatchers
Authors: Pearson Talima , Whitfield Mary J. , Theimer Tad C. , Keim Paul
Published: September 2019

Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extra-pair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 ± 0.35 offspring per season, compared to 1.15 ± 0.18 for monogamous males. This increased reproductive success was due primarily to the increased number of nests of polygynous males, as the number of offspring per pair did not differ between monogamous and polygynous males. Twenty of the 140 genotyped nestlings were extra-pair offspring. Sires could be assigned to 16 of these; one polygynous male sired two EPO in one nest, two monogamous males sired eight EPO in two nests, and four nonterritorial males sired six EPO in four nests. Overall, these results indicate that in this population, females of polygynous males did not raise a disproportionate number of EPO as a result of the polygynous mating strategy of their mate, and that both territorial and nonterritorial males sired EPO.
Breeding Strategies of a Socially Monogamous Neotropical Passerine: Extra-Pair Fertilizations, Behavior, and Morphology
Authors: Carvalho Carlos B. V. , Macedo Regina H. , Graves Jefferson A.
Published: September 2019

Blue-black Grassquits (Volatinia jacarina) are small, granivorous, Neotropical birds that are abundant in central Brazil. During the reproductive season, the socially monogamous males acquire a blue-black plumage and defend very small, clustered territories that resemble leks. They execute a conspicuous courtship display that consists of a leap, revealing white under-wing patches, synchronized with a vocalization. We collected data on the morphology and behavior of banded males and characteristics of their territories to determine how these factors may influence acquisition of mates and nesting. For a second group of birds in the area, we used microsatellite genotyping to test the breeding synchrony hypothesis, which predicts that tropical species that breed synchronously should exhibit high rates of extra-pair fertilization (EPF). We found that males that successfully formed a pair bond differed from unsuccessful males in their behavior, but not in morphological attributes or territory features. Successful males spent more time in their territories, executed displays for longer periods and at greater rates, and their display leaps were higher. These results point to the greater importance of behavior relative to other factors in the successful reproduction of Blue-black Grassquit males. In the second group of birds, EPFs occurred in 63% of 11 nests and involved 50% of the 20 chicks sampled. This exceptionally high incidence of EPF in the small sample analyzed occurred in diverse contexts, including intraspecific parasitism and quasi-parasitism, a rare type of maternity loss where the resident female is parasitized by other females that were fertilized by the resident male. A short and highly synchronized breeding season, clustered breeding in small territories, and granivorous habits may contribute to the high rates of EPF in this tropical species.
Changes in Egg Size and Clutch Size with Elevation in a Wyoming Population of Mountain Bluebirds
Authors: Johnson L. Scott , Ostlind Emilene , Brubaker Jessica L. , Balenger Susan L. , Johnson Bonnie G. P. , Golden Harold
Published: September 2019

Few studies have examined how avian life-history traits vary within populations as elevation increases and climate becomes more severe. We compared egg and clutch sizes of Mountain Bluebirds (Sialia currucoides) nesting at two elevations (1500 m and 2500 m above sea level) in the Bighorn Mountains of Wyoming over two years. Eggs laid by females at the high-elevation site were, on average, significantly (6%) smaller in volume than eggs laid by their lower-elevation counterparts. Across elevations, egg size showed a significant positive correlation with female body condition (weight relative to size), and high-elevation females had significantly lower indices of condition than low-elevation females. Temperatures during clutch formation were colder at the high-elevation site, and egg size was negatively related to temperature after controlling for the effects of female condition. Clutches of females at high elevations were, on average, marginally smaller (by 5%, 0.3 eggs) than clutches of low-elevation females. Unlike egg size, clutch size was unrelated to either female condition or temperature during clutch formation. This suggests that, when under energetic or nutritional stress at high elevations, females sacrifice egg size before sacrificing clutch size.
Chick Growth Variability and Parental Provisioning in the Magnificent Frigatebird
Authors: Tobón Emilio , Osorno José Luis
Published: September 2019

In two contrasting breeding seasons, we investigated the effects of provisioning on chick growth and survival of the Magnificent Frigatebird (Fregata magnificens), a socially monogamous, dimorphic seabird that rears a single chick for more than a year, shows specialized feeding techniques, and depends on unpredictable food sources. We hypothesized that chicks of this seabird would increase their chances of survival by varying their growth in relation to food availability. We estimated the amount of food ingested by a chick using electronic scales placed at the nest and recorded feeding rates, growth rate, fledging size, and fledging age. Body mass and bill and ulna lengths were also measured. Not surprisingly, provisioning and growth were higher in the year with apparently higher food availability; however, developmental variables did not show the same pattern. This work shows a clear relationship between provisioning and growth and that growth variability occurs in this species. Understanding the relationship between provisioning and growth provides insight into life histories and elucidates the influence of variation in provisioning on fitness.