bluuebunny/crossref_metadata_2025 huggingface dataset:
Density-Dependent Mass Gain by Wilson's Warblers During Stopover
Authors: Kelly Jeffrey F. , DeLay Linda S. , Finch Deborah M.
Published: September 2019

The need restore energetic reserves at stopover sites constrains avian migration ecology. To describe that constraint, we examined relationships among mass gained by Wilson's Warblers (Wilsonia pusilla) during stopover, abundance of Wilson's Warblers (i.e. capture rate), and arthropod abundance during autumn migration. We found that amount of mass gained by Wilson's Warblers during stopover declined as a function of their abundance. We found no relationship between mass gained by Wilson's Warblers and arthropod abundance. Abundance of Wilson's Warblers was positively associated with arthropod abundance. These patterns are consistent with the hypothesis that mass gain during stopover is density dependent. They also suggest that Wilson's Warblers respond numerically to abundance of food at that stopover site. This numerical response may override any functional response and thereby account for lack of a relationship between mass change and arthropod abundance.
Growth and Development of Prefledging Canada Geese and Lesser Snow Geese: Ecological Adaptation or Physiological Constraint?
Authors: Badzinski Shannon S. , Ankney C. Davison , Leafloor James O. , Abraham Kenneth F.
Published: September 2019

Neonate, gosling, and adult Canada Geese (Branta canadensis interior) and Lesser Snow Geese (Chen caerulescens caerulescens) were collected to evaluate if growth rates and developmental patterns differed interspecifically and to determine if such differences were better explained by physiology of the growth process or by ecological conditions historically experienced by those two species. Patterns of growth and development of Canada and Lesser Snow goose goslings were similar to those reported for other Arctic geese, but differences in relative growth rates and developmental patterns of external structures, digestive organs, and skeletal muscles were observed between these two species. As compared to Canada Geese, body parts associated with locomotion and acquisition or processing of food generally increased at relatively faster rates and were more developed relative to adult size in Lesser Snow Geese. Relative rates of increase for carcass protein and body mass in these two species did not support a physiological constraint on growth. Rates and patterns of growth and development were better explained as adaptations to ecological factors, such as growing season and nesting or brood rearing conditions, historically experienced by these two species.
Brown-Headed Cowbird Parasitism of Ovenbirds in Suburban Forest Fragments
Authors: Hersek Marta J. , Frankel Michelle A. , Cigliano John A. , Wasserman Frederick E.
Published: September 2019

Forest fragmentation in North America concerns many biologists because of its effects on wildlife populations. One group that has demonstrated particular sensitivity is Neotropical migrant birds. We studied Ovenbirds (Seiurus aurocapillus) in forest fragments in a suburban landscape in eastern Massachusetts to determine effects of cowbird parasitism on Ovenbird reproductive success. Our three large (120–312 ha) and six small (10–59 ha) forests were all smaller than most of those studied by other researchers, and they were surrounded by wooded suburban lots rather than agricultural land. Twenty-nine percent of nests found were parasitized by cowbirds; that frequency is lower than other investigators have reported for small, isolated fragments. The number of Ovenbirds fledged in successful parasitized (x̄ = 2.4) and unparasitized (x̄ = 3.8) nests was similar to other studies. Cowbirds were found to remain in nests for one to two days after their Ovenbird nestmates fledged. Differences in parasitism rate between this and other Ovenbird studies may be related to landscape characteristics. Ovenbirds nesting in small fragments in relatively wooded landscapes, as was the case in this study, have higher reproductive success than do Ovenbirds nesting in similar-sized fragments within an agricultural landscape. Using Ovenbirds as a model for neotropical migrants, we suggest that small fragments in a landscape with relatively wooded connections between forested areas may allow migrants to attain higher reproductive success than similar sized forests surrounded by agricultural land.
Patterns of Egg Laying and Breeding Success in Humboldt Penguins (Spheniscus Humboldti) at Punta San Juan, Peru
Authors: Paredes Rosana , Zavalaga Carlos B. , Boness Daryl J.
Published: September 2019

We analyzed patterns of egg laying and breeding frequency of Humboldt Penguins (Spheniscus humboldti) between 1993 and 1997 at Punta San Juan, Peru. Egg-laying extended from mid-March to the first week of December, showing two well-defined peaks in April and August–September. The extended breeding period of these birds was the result of individuals having a second clutch. About half of the females (n =189) had two clutches per year, most of which were double broods (73%). The date of completion and outcome of reproduction, or whether a change of mates occurred from the previous year, did not affect timing of egg laying. The majority of first clutches (62%) were laid in April each year. Two-clutch breeders that started laying eggs early in April had a higher breeding success than those starting in late April, and double brooders had greater success than single brooders. Two-clutch breeders started to lay eggs earlier than single-clutch breeders. Taking into account that a penguin breeding cycle (from egg laying to fledging) lasts ∼4 months, laying eggs early in April increases the chance of rearing two successful broods per year. During three consecutive years, females tended to have two clutches instead of only one clutch and an average breeding success of 4.54 fledglings over 3 years. Having as many clutches as possible when conditions are favorable appears to be a strategy used by Humboldt Penguins to maximize their lifetime reproductive success within a productive but unpredictable environment.
Diagnosability Versus Mean Differences of Sage Sparrow Subspecies
Authors: Patten Michael A. , Unitt Philip
Published: September 2019

A subspecies is a collection of populations within a biological species that are diagnosably distinct from other such collections of populations. That infraspecific designation has motivated a litany of spirited debates over the past half-century, from impassioned pleas for its retention to heated outcries for its abolition. We believe that the vast majority of attacks on the subspecies concept have resulted from displeasure with its improper application, not from serious flaws in the concept itself. The recognition of diagnosable subspecies allows one to address many questions not easily answered otherwise, ranging from dispersal and migration to local selection and adaptation and biogeographic affinities, yet that goal was lost for many years. Many taxonomists in the late nineteenth century and first half of the twentieth century named subspecies on the basis of average differences between populations under study, a procedure at odds with identification of diagnosable populations. To resolve that dilemma, we make explicit the established 75% rule for subspecies recognition, including formalizing the rule and developing a simple statistic to test whether diagnosability is met. The equations can be adapted readily to any level of diagnosability. We apply the concept and the statistic to a revision of the subspecies of the Sage Sparrow (Amphispiza belli). Rather than the seven named subspecies or the five that are generally considered valid, we show that only three aggregates of populations are diagnosable, and thus only three subspecies should be recognized: (1) A. b. belli in chaparral and sage scrub of coastal California, northwestern Baja California, and San Clemente Island; (2) A. b. cinerea in desert scrub of west-central Baja California; and (3) A. b. nevadensis in sagebrush and saltbush of the Great Basin and interior California. Consistent application of the 75% rule will result in fewer trinomials and a more biologically meaningful and taxonomically useful subspecies concept.
Body Condition and Parental Decisions in the Snow Petrel (Pagodroma Nivea)
Authors: Tveraa Torkild , Christensen Guttorm N.
Published: September 2019

In Procellariiformes, parents guard the chick for some time after it has attained homeothermy. Such a strategy may have evolved to protect the chick from predation or inclement weather, but it is costly because only one parent can forage at a time. Therefore, the decision to leave the chick seems to be a trade-off between the chick's ability to care for itself, body condition of the parent present at the nest, and ability of the bird out foraging to return to the nest before its mate's body condition has degraded. We studied chick growth and survival together with number of days Snow Petrel (Pagodroma nivea) chicks were guarded before being left alone for the first time in relation to the parents body condition and ability to return to the nest in time. Parents in good body condition were more likely to produce a chick that survived the guard stage. They also guarded their chick for a longer period (range 2–8 days, x̄ = 4.5) and finally left it alone with a higher body mass than those in poor body condition. However, whether the foraging bird was able to return to the nest in time to relieve its mate was also strongly related to number of days the chick was guarded and its body mass. The chicks' survival from when they were left alone and until day 10 posthatch was positively related both to number of days they were guarded and their body condition (body mass corrected for age).
Double Sampling to Estimate Density and Population Trends in Birds
Authors: Bart Jonathan , Earnst Susan
Published: September 2019

We present a method for estimating density of nesting birds based on double sampling. The approach involves surveying a large sample of plots using a rapid method such as uncorrected point counts, variable circular plot counts, or the recently suggested double-observer method. A subsample of those plots is also surveyed using intensive methods to determine actual density. The ratio of the mean count on those plots (using the rapid method) to the mean actual density (as determined by the intensive searches) is used to adjust results from the rapid method. The approach works well when results from the rapid method are highly correlated with actual density. We illustrate the method with three years of shorebird surveys from the tundra in northern Alaska. In the rapid method, surveyors covered ∼10 ha h–1 and surveyed each plot a single time. The intensive surveys involved three thorough searches, required ∼3 h ha–1, and took 20% of the study effort. Surveyors using the rapid method detected an average of 79% of birds present. That detection ratio was used to convert the index obtained in the rapid method into an essentially unbiased estimate of density. Trends estimated from several years of data would also be essentially unbiased. Other advantages of double sampling are that (1) the rapid method can be changed as new methods become available, (2) domains can be compared even if detection rates differ, (3) total population size can be estimated, and (4) valuable ancillary information (e.g. nest success) can be obtained on intensive plots with little additional effort. We suggest that double sampling be used to test the assumption that rapid methods, such as variable circular plot and double-observer methods, yield density estimates that are essentially unbiased. The feasibility of implementing double sampling in a range of habitats needs to be evaluated.
Landbird Counting Techniques: Current Practices and an Alternative
Authors: Rosenstock Steven S. , Anderson David R. , Giesen Kenneth M. , Leukering Tony , Carter Michael F.
Published: September 2019

Counting techniques are widely used to study and monitor terrestrial birds. To assess current applications of counting techniques, we reviewed landbird studies published 1989–1998 in nine major journals and one symposium. Commonly used techniques fell into two groups: procedures that used counts of bird detections as an index to abundance (index counts), and procedures that used empirical models of detectability to estimate density. Index counts rely upon assumptions concerning detectability that are difficult or impossible to meet in most field studies, but nonetheless remain the technique of choice among ornithologists; 95% of studies we reviewed relied upon point counts, strip transects, or other index procedures. Detectability-based density estimates were rarely used and deserve wider application in landbird studies. Distance sampling is a comprehensive extension of earlier detectability-based procedures (variable-width transects, variable circular plots) and a viable alternative to index counts. We provide a conceptual overview of distance sampling, specific recommendations for applying this technique to studies of landbirds, and an introduction to analysis of distance sampling data using the program DISTANCE.
Energetic Consequences of Clutch Temperature and Clutch Size for a Uniparental Intermittent Incubator: The Starling
Authors: Reid J. M. , Ruxton G. D. , Monaghan P. , Hilton G. M.
Published: September 2019

In uniparental intermittent incubators, incubating parents must simultaneously regulate both the temperature of the clutch and their own energy level. To examine energetic consequences of providing different thermal environments for clutches of different sizes, a dynamic model was constructed in which energy level of an incubating European Starling (Sturnus vulgaris) and temperature of its clutch were simultaneously described. Adult energy balance after a day of incubation decreased as mean clutch temperature increased, such that the debt accrued while maintaining a clutch within the optimal developmental temperature range (36–39°C) was predicted to be prohibitively high, despite the prediction that the mean basal metabolic rate (BMR) required to maintain this temperature was <2 BMR. Thus, this model can explain our observation that starlings maintained their eggs at 32–33°C, well below the developmental optimum. Consistent with empirical studies, our model predicted that the metabolic demand of incubation increases with clutch size. That increase was predicted to affect adult energy balance and hence cost of incubation when starlings maintained their clutches at optimal temperatures, but not at the lower temperatures actually observed. Hence, clutch-size-dependent variation in incubation demands may be unlikely to influence optimal number of eggs that a starling should lay. However, exact relationship between clutch size and adult energy debt depended on the nature of the relationship between clutch size and clutch thermal properties and on mean incubation temperature. Thus, consequences of clutch size for the cost of incubation are not clearly predictable, and caution may be required when using experimental clutch enlargements to manipulate reproductive costs.
A Robust Phylogeny of the Oropendolas: Polyphyly Revealed by Mitochondrial Sequence Data
Authors: Price J. Jordan , Lanyon Scott M.
Published: September 2019

We present a robust, fully resolved phylogeny for the oropendolas that will serve as a basis for comparative studies in this group. We sequenced 2,011 base pairs (bp) of the mitochondrial cytochrome-b and ND2 genes from 22 individuals to reconstruct relationships between recognized species and subspecies and to assess variation within polytypic taxa. A single phylogenetic tree was produced despite the use of a wide range of weighting schemes and phylogenetic reconstruction methods. Our data provide strong evidence that oropendolas are polyphyletic, with two distinct groups within a larger clade of oropendolas and caciques. We confirm the monophyly of recognized species, but indicate that some within-species relationships do not conform to recognized subspecies limits. Our findings thus demonstrate the importance of including multiple exemplars from each taxon of interest. The two genes provided complimentary and equally effective phylogenetic information for comparisons within the oropendolas, but exhibited lower resolution in comparisons above the species level.
Geographic Variation and Dialects in Songs of the Bronzed Cowbird (Molothrus Aeneus)
Authors: Warren Paige S.
Published: September 2019

Vocal dialects have presented a puzzle for evolutionary biologists for nearly 50 years. However, there is still a dearth of detailed description of variation in species with dialects, especially regarding acoustic characteristics that discriminate among dialects. In this study, I show that dialects occur in the “flight whistle” song type of the Bronzed Cowbird (Molothrus aeneus). Dialects in this species occur at a very large scale, spanning hundreds of kilometers. A discriminant function analysis revealed that the initial element of the song shows greater differences among dialects than a major element in the final portion of the song. This quantitative analysis of the dialect system provides the basis for understanding how Bronzed Cowbirds recognize songs from different dialects.
Evolution of Breeding Systems in Acrocephaline Warblers
Authors: Leisler Bernd , Winkler Hans , Wink Michael
Published: September 2019

Comparative analyses constitute an important complement to studies of adaptive behavior. Previous studies of avian mating systems considered the role of paternal care and habitat type on the evolution of polygyny. We extended those studies and included in our analyses the role of habitat quality, as characterized by food supply. Species in the monophyletic lineage of acrocephaline warblers (Acrocephalus, Chloropeta, Hippolais) are widely distributed, inhabit a variety of different habitats, and show a variety of breeding systems. We present a phylogenetic analysis of parental care and mating system characteristics in relation to ecological traits in 17 species. On the basis of a molecular phylogeny, we reconstructed patterns of changes from social monogamy to polygyny, and in paternal brood care. Specifically, we analyze the coevolution of brood care participation of males and social system, and how it relates to habitat quality. Furthermore, we assessed the phylogenetic inertia of mating systems. We found support for the hypothesis that change to highly productive habitats was associated with a greater emancipation of males from brood care, and with polygyny and promiscuity. Poor habitats, on the other hand, were associated with monogamy and the occurrence of helpers. In contrast to some morphological characters, mating systems appear to be phylogenetically labile.
Nest-Site Reuse Patterns for a Cavity-Nesting Bird Community in Interior British Columbia
Authors: Aitken K. E H. , Wiebe K. L. , Martin K.
Published: September 2019

Most obligate cavity-nesting birds are considered to be nest-site limited, either by time or energy to excavate or to acquire suitable holes for nesting. We examined rates of nest-cavity reuse for a rich community of cavity-nesting birds in mixed forests in interior British Columbia. Using a sample of 402 cavity-reuse cases over five years, we measured cavity reuse for 20 cavity-nesting bird and mammal species (three guilds), and examined the relationship between nest-cavity reuse and features of cavities, nest trees, and forest stands. Eight percent of used cavities were destroyed between years. Reuse rates were 17% for the cavities of weak excavators such as nuthatches and chickadees, 28% for formerly active woodpecker nests, and 48% for cavities previously used by secondary cavity nesting birds, but there was considerable species variation within all guilds. Nest cavities in aspen that were deep with large entrances had the highest reuse. At the forest stand level, cavities in trees close to edges and in sites with more edge habitat had greater reuse. Reused cavities tended to be occupied in sequential years rather than being inactive for a year. With increasing amounts of managed landscapes, availability of suitable cavities for forest nesting vertebrates is decreasing. Reuse of existing cavities might help mitigate the problem of nest-site limitation.
Osmoregulation by Nestling and Adult American Kestrels (Falco Sparverius)
Authors: Lyons Michele E. , Goldstein David L.
Published: September 2019

We explored aspects of renal function in American Kestrels (Falco sparverius), birds that habitually eat high-protein meals. In particular, we hypothesized that, like granivorous birds switched to high-protein food, kestrels would have high urine flows with high proportions of waste N as urate. In nestlings in the field, 80–93% of urinary N was in the form of urate, though concentrations of ammonia and urea were higher in older nestlings. Feeding resulted in reduced osmotic and ion concentrations in urine, but concentrations and proportions of nitrogenous wastes were unaffected. In adult kestrels in the laboratory, urine flow rate in fed animals, ∼1 mL h–1, was similar to that previously measured in avian granivores. Urine flow declined with fasting, accomplished by both a reduction in glomerular filtration rate (significant after 24 h fast) and a rise in tubular water reabsorption (significant after 48 h). During the course of a 48 h fast, proportion of urinary N excreted as urate fell and that as ammonia rose. Both filtration and secretion of urate dropped during fasting, so that tubular secretion remained responsible for ∼90% of urinary urate. Composition of fluid voided from the cloaca differed little from that of the ureteral urine.
Colony Choice in Cliff Swallows: Effects of Heterogeneity in Foraging Habitat
Authors: Brown Charles R. , Sas Christine M. , Brown Mary Bomberger
Published: September 2019

One potential determinant of colony size in birds is the local availability of food near a nesting site. Insectivorous Cliff Swallows (Petrochelidon pyrrhonota) in southwestern Nebraska nest in colonies ranging from 2 to over 3,000 nests, but they feed on so many kinds of insects that direct sampling of food resources is impractical. Instead, we investigated the degree to which swallow colony size was correlated with the extent of different habitat types, land use diversity, and plant species diversity in the colony's foraging range, and used those parameters as indices of potential variation among sites in food availability. Amount of flowing and standing water in the foraging range was a significant predictor of mean colony size across years at a site, with larger colonies associated with more water. The same result held for most years when analyzed separately. The extent of flowing water in the foraging range also was a significant predictor of the frequency with which a site was occupied across years. In addition, univariate tests suggested that the amount of cultivated cropland in the foraging range varied inversely with colony size. Land use diversity, as measured by Simpson's index, increased significantly with colony size, and all of the sites with perennially very large colonies (mean colony size >1,000 nests) were associated with foraging ranges of relatively high land use diversity. Repeatability of colony size across years differed significantly from zero across all sites, but repeatabilities were significantly lower (colony sizes less similar between years) for sites situated in low-diversity habitats and for sites used less often. There was no strong effect of plant species diversity within the foraging range on either colony size at a site or likelihood of site use. We conclude that land use diversity per se (and possibly the extent of water near a site) might influence insect distribution and constrain formation of the larger colonies to certain sites. These findings emphasize that colony choice in Cliff Swallows is complex, reflecting both the socially mediated costs and benefits of group size that vary among individuals and the effects of habitat heterogeneity that may influence food availability at some sites.
Antipredation Value of Colonial Nesting in Yellow-Headed Blackbirds
Authors: Picman Jaroslav , Pribil Stanislav , Isabelle Andre
Published: September 2019

Yellow-headed Blackbirds (Xanthocephalus xanthocephalus) in Manitoba breed in dense colonies in cattail marshes. Their reproductive success is affected mainly by predation. The most important predator on blackbird nests is the Marsh Wren (Cistothorus palustris), which breaks blackbird eggs and kills small nestlings. We examined whether colonial nesting in Yellow-headed Blackbirds may represent an adaptation to reduce Marsh Wren predation. Marsh Wren predation may be reduced by (1) mutual nest defense by adult blackbirds, (2) predator satiation or dilution, or (3) selfish-herd effects. We tested these hypotheses using experimental nests and found that their safety increased with decreasing distance to the nearest blackbird nest and with increasing density of simultaneously active blackbird nests located nearby. Safety also was higher for nests placed inside a blackbird colony rather than outside. These findings support the nest-defense hypothesis. We also found that Marsh Wrens are capable of destroying a whole blackbird colony in a few days, and that colony size is not correlated with nest safety. These results suggest that the satiation or dilution benefits are negligible. Finally, we found that central nests are safer than peripheral nests in a blackbird colony, but not in an artificial colony, providing weak support for the selfish-herd hypothesis. We conclude that nest predation is reduced mainly by mutual nest defense of adult birds and may represent an important selective force favoring colonial nesting in this species.
Short- and Long-Term Effects of Male-Like Concentrations of Testosterone on Female European Starlings (Sturnus Vulgaris)
Authors: De Ridder Elke , Pinxten Rianne , Mees Veerle , Eens Marcel
Published: September 2019

European Starlings (Sturnus vulgaris) exhibit marked sex differences in behavior during spring. Song activity, nest-box occupation, the carrying of green nesting materials into a nest hole (typical mate-attraction behaviors), and aggression occur much more frequently in males who also have higher testosterone (T)-levels than females. Here, we examined whether male-like concentrations of T would activate these behaviors in female starlings. We treated females with implants that were either empty (C-females) or packed with T (T-females) during late December. Although elevated T-levels significantly increased song activity in females, the proportion of time spent singing was still much lower than in males. T-treatment in females also failed to induce singing behavior in the nest box, a typical male mate-attraction behavior. Those results suggest both activational and organizational effects of T on singing. Nest-box occupation, carrying of green nesting material into a nest hole, and aggressive behavior were not activated by elevated T-levels, indicating that sex differences in these behaviors are probably based on early organizational effects of steroid hormones. We also evaluated effects of increased T-concentrations on some physiological, morphological, and immunological parameters. T-treatment strongly suppressed tail feather regrowth after experimental plucking, and also delayed onset of molt of wing feathers and slowed its progress. T-implantation caused color of the bill to change from black to yellow, but did not affect body mass. Immune function was determined by using two indirect measures: blood composition (haematocrit and buffy coat values) and indications of infections. Although haematocrit and buffy coat values did not differ between C- and T-females, T-females were significantly more infected with Staphylococcus aureus than C-females at the end of the experiment.
Does Increasing Daylength Control Seasonal Changes in Clutch Sizes of Northern Pintails (Anas Acuta)?
Authors: Krapu Gary L. , Sargeant Glen A. , Perkins Alison E. H.
Published: September 2019

We evaluated spatiotemporal variation in clutch sizes of Northern Pintails (pintails; Anas acuta) nesting in California (1985 to 1996), North Dakota (1982 to 1985), Saskatchewan (1982 to 1985) and Alaska (1991 to 1993) to determine whether seasonal declines in clutch size varied in ways that were consistent with a controlling influence of increasing day length. Pintails began nesting in mid-March in California, mid-April in North Dakota and Saskatchewan, and mid-May in Alaska. Observed durations of nesting were 70 ± 2.6 days (SE) in California, 60 ± 6.3 days in North Dakota, 66 ± 1.3 days in Saskatchewan, and 42 ± 0.7 days in Alaska. Annual differences were the principal source of variation in mean clutch sizes (σ̂Y2 = 0.15, SE = 0.049), which varied little among study locations (σ̂A2 = 0.002, SE = 0.013). Predicted rates of seasonal decline in clutch sizes increased with latitude early in the nesting season, but declined as the nesting season progressed, except in California. Rates of decline in clutch sizes thus were not directly related to rates of increase in day length. Predicted declines in numbers of eggs per clutch over the nesting season were similar for all four locations (range, 3.05–3.12) despite wide variation in durations of nesting. Evidence suggests that reduced nutrient availability during nesting contributes to a higher rate of decline in clutch sizes in Alaska than in temperate regions. Pintails that nest early lay large initial clutches, but thereafter clutch sizes decline rapidly and breeding terminates early. This reproductive strategy is adaptive because young that hatch earliest exhibit the highest survival rates; however, the conversion of grassland to cropland on the primary prairie breeding grounds has reduced hatching rates of clutches laid early in the nesting season. Under these conditions, the limited capacity to renest in late spring on their prairie breeding grounds probably has contributed to Pintail population declines.
Systematics of Large White-Headed Gulls: Patterns of Mitochondrial DNA Variation in Western European Taxa
Authors: Crochet Pierre-André , Lebreton Jean-Dominique , Bonhomme François
Published: September 2019

Although the large white-headed gull group (genus Larus) has long been a model in speciation studies, the systematic status and evolutionary relationships of many of its taxa remain unresolved. We used mitochondrial DNA control region and cytochrome-b gene sequences in an attempt to resolve some of those uncertainties. In contrast to previously published results based on nuclear markers, mitochondrial DNA was found to be strongly structured among species, indicating that mitochondrial gene flow is very low. Phylogenetic relationships remain largely unresolved, mainly because of the low amount of variation between species. Horizontal transfer of mitochondrial lineages is demonstrated or suspected between most taxa and obscured the reconstruction of the history of the group. The Mediterranean form michahellis was as differentiated from the other western European species as these are from each others, confirming it is neither conspecific with L. fuscus nor with L. argentatus. The forms fuscus and graellsii do not show any significant differences in haplotypes frequencies, arguing for their subspecific status.
Molecular Systematics and the Role of The “Várzea”–“Terra-Firme” Ecotone in the Diversification of Xiphorhynchus Woodcreepers (Aves: Dendrocolaptidae)
Authors: Aleixo Alexandre
Published: September 2019

The phylogeny of all known Xiphorhynchus (Dendrocolaptidae) species and many of its subspecies was reconstructed to evaluate species limits in this taxonomically challenging genus and investigate the possible role played by the Amazonian “várzea” (floodplain forest)–“terra-firme” (upland forest) ecotone in its diversification. Phylogenies were inferred based on 2,430 bp of the mitochondrial DNA genes ND2, ND3, and cytochrome b. All phylogeny estimates supported the monophyly of all extant Xiphorhynchus species to the exclusion of the sibling species pair Straight-billed (X. picus) and Zimmer's (X. kienerii) woodcreeper. Confirming findings of previous molecular and anatomical studies, strong support was found to include the Lesser Woodcreeper (Lepidocolaptes fuscus) in Xiphorhynchus. Levels of sequence divergence among some subspecies of Buff-throated (X. guttatus), Ocellated (X. ocellatus), and Spix's (X. spixii) woodcreepers reached or exceeded those found between closely related, undisputed biological species of Xiphorhynchus. High levels of sequence differentiation and the paraphyly of some Xiphorhynchus species indicated that the following taxa should be recognized as species: Lafresnaye's (X. guttatoides), Tschudi's (X. chunchotambo), and Elegant (X. elegans) woodcreepers. All Xiphorhynchus species restricted to terra-firme forest in lowland Amazonia formed a well supported monophyletic group, whereas species restricted to várzea forest were either basal to a clade containing species found in a wide variety of habitats (Striped Woodcreeper [X. obsoletus]) or belonged to a distinct lineage likely to be regarded as a separate genus (X. kienerii). These findings falsified an anticipated sister relationship between várzea and terra-firme species, as expected if the várzea–terra-firme ecotone had played a decisive role in population differentiation and speciation within Xiphorhynchus. Instead, phylogeny estimates suggested that the várzea–terra-firme habitat specialization evolved early on in the evolutionary history of Xiphorhynchus and that subsequent differentiation occurred mostly within the terra-firme habitat.
Grounded Ground Birds and Surfing Canopy Birds: Variation of Foraging Stratum Breadth Observed in Neotropical Forest Birds and Tested With Simulation Models Using Boundary Constraints
Authors: Walther Bruno A.
Published: September 2019

Vertical stratification of bird species has been intensively studied in temperate as well as tropical forest bird communities. One question that has received less attention is the variation of foraging stratum breadth. Hypotheses trying to explain that variation are based on differences in perception, evasion, adaptation, competition, and environmental and geometric boundary constraints. Although some predict that foraging strata near the ground should be narrower than those near the canopy, others predict that strata in the midstory should be broadest. These hypotheses were tested using observational data of 92 rainforest bird species. Observations were made from or near a 40 m high canopy crane situated close to the Surumoni River (3°10′N, 65°40′W) near Esmeralda, Estado Amazonas, southern Venezuela (Surumoni-Crane-Project). I found a highly significant parabolic relationship between mean foraging height and its standard deviation showing that midstory bird species foraged in a broader stratum than either understory or canopy species. Using a conservative comparative method, I also showed that the relationship was not the result of the phylogenetic relatedness of the species involved. Analysis of previously published data supports the relationship for two other tropical avifaunas. Because the ground and the outer canopy represent geometric boundaries to the movement of most forest birds, two simulation models were used to test whether midstory species may simply have a broader stratum because they are less constrained in their movements than species near the boundaries. The “random model” allowed individuals to move randomly between the two boundaries. It illustrated that boundary constraints alone cannot explain the observed parabolic relationship. In the “preference model,” individuals tended to move back to their preferred height within the forest column. That model simulated the observed parabolic relationship once a sufficient number of time steps had been reached, suggesting that a simple combination of geometric boundaries and preference for a specific foraging height may generate narrower strata near the boundaries. The other hypotheses only explain the parabolic relationship if other factors (e.g. vegetation density) are vertically distributed in such a way as to generate the observed parabolic pattern. Finally, I briefly discuss the advantages and disadvantages of using raw data in across-species analyses versus corrected data in phylogenetically-controlled analyses.
What is a Wood-Warbler? Molecular Characterization of a Monophyletic Parulidae
Authors: Lovette I. J. , Bermingham E.
Published: September 2019

The wood-warblers (family Parulidae) fall within a radiation of passerine birds commonly known as the New World nine-primaried oscines. Defining familial relationships within that radiation has previously been challenging because of its extremely high diversity, a paucity of phylogenetically informative morphological characters, and an apparent high rate of cladogenesis early in the radiation's history. Here, analyses of mitochondrial and nuclear DNA sequences demonstrate that the 25 extant genera traditionally placed in the Parulidae do not form a monophyletic group. Instead, all reconstructions identify a well-resolved clade of 19 genera (Vermivora, Parula, Dendroica, Catharopeza, Mniotilta, Setophaga, Protonotaria, Helmitheros, Limnothlypis, Seiurus, Oporornis, Geothlypis, Wilsonia, Cardellina, Ergaticus, Myioborus, Euthlypis, Basileuterus, and Phaeothlypis) that are all morphologically typical wood-warblers traditionally placed in the Parulidae. Six genera traditionally assigned to the Parulidae—Microligea, Teretistris, Zeledonia, Icteria, Granatellus, and Xenoligea—fall outside this highly supported clade in all mtDNA-based and nuclear DNA-based reconstructions, and each is probably more closely allied to taxa traditionally placed in other nine-primaried oscine families. The long, well-supported, and independently confirmed internode at the base of this wood-warbler clade provides the opportunity to define a monophyletic Parulidae using several complementary molecular phylogenetic criteria. Support for those relationships comes from reconstructions based on a range of nucleotide-intensive (from 894 to 3,638 nucleotides per taxon) and taxon-intensive (45 to 128 species) analyses of mtDNA sequences, as well as independent reconstructions based on nucleotide substitutions in the nuclear-encoded c-mos gene. Furthermore, the 19 typical wood-warbler genera share a synapomorphic one-codon c-mos deletion not found in other passerines. At a slightly deeper phylogenetic level, our mtDNA-based reconstructions are consistent with previous morphologic and genetic studies in suggesting that many nine-primaried oscine taxa have unanticipated affinities, that many lineages arose during an early and explosive period of cladogenesis, and that the generation of a robust nine-primaried oscine phylogeny will require robust taxonomic sampling and extensive phylogenetic information.
Phylogeny of the Tyrant Flycatchers (Tyrannidae) Based on Morphology and Behavior
Authors: Birdsley Jeffrey S.
Published: September 2019

Previously published morphological and behavioral data for the tyrant flycatchers (Tyrannidae) were reanalyzed using cladistic techniques. Several additional characters, including two putative synapomorphies of the Tyrannidae were incorporated. Nearly all of the ∼100 traditional tyrannid genera were included. Results of the analysis of this set of 68 characters support three previously proposed tyrannid assemblages: the kingbird assemblage and slightly restricted Empidonax and Myiarchus assemblages. Characters of the nasal septum that past workers have considered conservative and phylogenetically informative are supported as synapomorphies of the kingbird and restricted Empidonax assemblages. Several small monophyletic groups of genera are supported. The monophyly of neither the Elaenia assemblage nor the flatbill and tody-tyrant assemblage is supported in any most-parsimonious tree, but such trees are not significantly better than trees supporting their monophyly. A Tyrannidae exclusive of the Cotingidae and Pipridae is monophyletic in some most-parsimonious trees, but not in others in which flatbills and tody-tyrants are basal to a clade containing Cotingidae, Pipridae, and the remaining tyrannid genera. There is some evidence that characters describing plumage color pattern are more homoplasious than the other character suites I examined.
Age-Related Trends in Different Aspects of the Breeding Performance of Individual Female Eurasian Sparrowhawks (Accipiter Nisus)
Authors: Newton Ian , Rothery Peter
Published: September 2019

Age-related trends in breeding performance of female Eurasian Sparrowhawks (Accipiter nisus) were examined in south Scotland. Over a 22 year period, most individuals were banded and of known age. Previous analyses had shown that average number of young raised per breeding attempt (or year) increased progressively in successive age-groups to midlife (around five years) and declined thereafter. Here we analyze different components of breeding performance (such as clutch-size, hatching and fledging success) to find which components contribute most importantly to the overall age-related trend in productivity. Most aspects of breeding showed a similar upward–downward trend through the life span, but the downward trend in productivity in later life could be attributed mainly to poorer nestling survival. In general, in each aspect of breeding, the mean trend of the population as a whole was followed by individuals studied at different ages. Such individual trends were sufficient to account for the overall mean trend, and there was no need to postulate that high-performance or low-performance birds entered and left the breeding population at different ages. Only one aspect of breeding showed no trend with age, namely proportion of birds that laid having built a nest, but that type of failure affected only a small proportion of individuals.
Estimating Species Richness of Tropical Bird Communities From Rapid Assessment Data
Authors: Herzog Sebastian K. , Kessler Michael , Cahill Thomas M.
Published: September 2019

Rapid assessment surveys of tropical bird communities are increasingly used to estimate species richness and to determine conservation priorities, but results of different studies are often not comparable due to the lack of standardization. On the basis of computer simulations and six years of field testing, we evaluated the recently proposed “20-species-list” survey method and statistical estimators for assessing species richness of tropical bird communities. This method generates a species-accumulation curve by subdividing consecutive observations of birds into lists of 20 species, thus relating cumulative species richness to the number of observations rather than time or space and thereby accounting for moderate differences in observer qualification and field conditions. Species accumulation curves from computer-simulated communities and two empirical data sets from Bolivia were analyzed with nine species richness estimators to evaluate estimator accuracy with respect to variations in species-list size, sample size, species-pool size, and community structure. For empirical and most simulated data sets, the MMMEAN estimator performed best, but it was more sensitive to differences in community structure than most other estimators. The CHAO 2 estimator, which was recommended by previous studies, performed reasonably well but was considerably more sensitive to sample size than MMMEAN. The bootstrap and first- and second-order jackknife estimators performed poorly. We recommend using MMMEAN or, when standard deviations of richness estimates are indispensable, CHAO 2 with 10-species lists for estimating species richness of tropical bird communities and propose a set of standard survey rules. Careful examination of estimator accumulation curves is required, however, and a technique based on the ratio between estimator and species accumulation curve is suggested to control for the confounding effects of sampling effort. Overall, the species-list method combined with statistical richness estimation is doubtlessly much more standardized and valuable than simple comparisons of one-dimensional locality lists and represents a promising tool for conservation assessment and the study of avian diversity patterns in the tropics.
Effects of Dispersal on Survival Probability of Adult Yellow Warblers (Dendroica Petechia)
Authors: Cilimburg Amy B. , Lindberg Mark S. , Tewksbury Joshua J. , Hejl Sallie J.
Published: September 2019

Annual survival probability estimates for songbirds are generally biased low because dispersal is not differentiated from mortality. Presently, knowledge of between-year breeding dispersal is lacking for most songbirds. To assess adult survival probabilities and dispersal, we color-banded and resighted 436 Yellow Warblers (Dendroica petechia) over five breeding seasons at 11 study sites in the Bitterroot Valley, Montana. During the last two of those seasons, we searched extensively for marked warblers between and surrounding those sites. We compared survival probabilities estimated with and without this added dispersal information and assessed the effectiveness of adjusting survival probabilities with transient-type models. Survival probabilities were calculated using open population models, and model selection was based on Akaike's Information Criterion (AIC) within program MARK. The best model indicated that survival probabilities differed between males and females and varied among years. We found that dispersal off the study site was common (in 1999, 30% of resighted birds were found off their original study site), and survival probabilities increased by 6.5–22.9% (0.02 ± 0.07−0.106 ± 0.06) with the inclusion of dispersed birds. We suggest that emigration can have substantial effect on survival probabilities and advise against the use of return rates from small study areas or spatial or temporal comparisons of return rates because of spatial and temporal variation in extent of emigration. In addition, our results suggest that additional assessments of the reliability of transient-type models under some sampling schemes may be warranted.
Cooperatively Breeding Groups of Carrion Crow(Corvus Corone Corone) in Northern Spain
Authors: Baglione Vittorio , Marcos José M. , Canestrari Daniela
Published: September 2019

The Carrion Crow (Corvus corone) is almost invariably reported as a species breeding as unassisted pairs, but a population of Carrion Crows (Corvus c. corone) from northern Spain that we have been studying since 1995 regularly exhibits cooperative breeding. The Spanish population thus demonstrates that cooperative breeding can vary greatly across populations. Most of the breeding territories (73.3%) in Spain were held by cohesive groups, which consisted of up to nine birds (mode = 3 birds). The proportion of fledglings that delayed dispersal for one year varied between 12.2 and 47.5% for different cohorts. The corresponding values for juveniles postponing dispersal for two years were 4.9 and 19.2%. Philopatry was skewed toward males. Some social groups contained immigrants. Therefore, delayed juvenile dispersal was not the only route towards sociality. Up to three helpers provided food to the nestling and at least one helper was found in all the groups surveyed. However, some group members refrained from visiting nests and thus the contribution to nestling care was highly variable among individuals.