bluuebunny/crossref_metadata_2025 huggingface dataset:
Offspring Desertion by Double-Brooded Female Barn Owls (Tyto Alba)
Authors: Roulin Alexandre
Published: September 2019

In double-brooded species, the sex that contributes less to breeding success may desert offspring before the end of the rearing period to start a new breeding attempt with another partner. I evaluated that prediction in the Barn Owl (Tyto alba), a species in which the male feeds the brood on average twice as often as the female. Among birds that produced a second brood, 46% of females and 4% of males deserted their offspring before completion of parental duties to remate with another partner at a distance of 1 to 10 km. Offspring desertion did not appear to incur a reproductive cost to the deserter, because deserting females at the first nest produced a similar number of offspring as nondeserting ones. In most cases, the new mate of deserting females had not been previously captured in the study area, and hence had probably not previously bred that season. Although the second clutch of deserting females was larger and produced two weeks earlier than that of nondeserting females, their nesting success did not differ.
Dendroplex (=Xiphorhynchus) Necopinus Zimmer 1934 (Dendrocolaptidae) is a Junior Synonym of Dendrornis Kienerii (=Xiphorhynchus Picus Kienerii) Des Murs 1855
Authors: Aleixo Alexandre , Whitney Bret M.
Published: September 2019

John T. Zimmer described Xiphorhynchus necopinus (Zimmer's Woodcreeper) as a sibling species of the more widespread Xiphorhynchus picus (Straight-billed Woodcreeper). Despite his initial suspicion that a preexisting name (kienerii) could be applied to the new species he described, Zimmer discarded that possibility without directly examining the type of X. p. kienerii housed at the Museum National D'Histoire Naturelle in Paris, France. We studied plumage and measured wing chord and tail lengths of the type specimen of X. p. kienerii, comparing it with series of specimens of X. necopinus and X. picus. We show that X. necopinus and the type of X. p. kienerii are morphologically and morphometrically indistinguishable, and thus necopinus is synonymized with kienerii, the name that has priority. Because Zimmer mistakenly applied the name kienerii to a western Amazonian population of X. picus, most specimens in museums identified as X. p. kienerii after Zimmer's review (Zimmer 1934) are likely to refer to X. p. peruvianus.
Falkland Island Sedge Wrens (Cistothorus Platensis) Imitate Rather Than Improvise Large Song Repertoires
Authors: Kroodsma Donald E. , Woods Robin W. , Goodwin Elijah A.
Published: September 2019

Among songbirds, does reduced fidelity to a breeding site lead to vocal improvisation? Data for Cistothorus wrens suggest it does, because North American Sedge Wrens (C. platensis) have low breeding-site fidelity and improvise their large song repertoires, but sedentary or site-faithful populations of this and other Cistothorus species in the Neotropics and North America all imitate. We attempted to falsify this hypothesis by studying extreme south-temperate zone populations of Sedge Wrens in the Falkland Islands. We banded and recorded males on Kidney Island and Carcass Island, and then compared song matching among males both within and between islands. Birds on those islands were highly site-faithful from one breeding season to the next. Song repertoires were large, up to 400 in one bird, and songs of birds within an island were more similar to each other than to songs on the other island, showing that these birds do imitate. These results further support the idea that site fidelity promotes imitation of neighbors, and continue to highlight the unique correlation between reduced site-fidelity and song improvisation in the North American Sedge Wren.
Richness and Composition of Oasis Bird Communities: Spatial Issues and Species–Area Relationships
Authors: Selmi Slaheddine , Boulinier Thierry , Barbault Robert
Published: September 2019

We used data on breeding bird communities of the oases of southern Tunisia to investigate variation in species richness and composition among local communities in relation to spatial configuration of the oasis system and to assess significance of the relationship between oasis size and local richness. Oases could be grouped into three regional systems, namely littoral, saharan, and mountainous oases. We found that at the scale of the entire oasis system, species richness and species composition exhibited significant spatial autocorrelation. That result was consistent with our prediction that the particular spatial organization of oases may have led to regional differences in availability of potential colonizers and that higher species exchange within oasis zones than among oasis zones may have played an important role in shaping local communities. With regard to the species–area relationship, we thus found that a model accounting for spatial covariance was more parsimonious than a standard regression model not incorporating information on the spatial location of oases. Overall, oasis size was a good predictor of species richness, but results were sensitive to spatial scale at which the relationship was examined. Aside from oceanic islands and forest patches, oases may constitute interesting systems to study how regional processes affect local diversity.
Reproduction and Survival in a Variable Environment: Ural Owls (Strix Uralensis) and the Three-Year Vole Cycle
Authors: Brommer Jon E. , Pietiäinen Hannu , Kolunen Heikki
Published: September 2019

We analyzed data on 535 Ural Owl (Strix uralensis) breeding attempts and consecutive survival of both adults and offspring from 1987–1998 in relation to the regional abundance of the Ural Owl's main prey, voles, which show a cycle of low, increase, and peak phases in their population numbers. Vole abundance varied up to 49×, crashing during spring–summer every three years. The breeding population tracked abundance of voles in the previous autumn with respect to percentage of pairs breeding and their reproductive output (laying date, clutch size), largely irrespective of phase. Survival depended on vole density in the preceding autumn, but was generally highest in the increase phase. There was thus a paradoxical situation in the peak phases, when vole populations crashed; the owls produced large clutches, but those survived poorly. Some adaptive and nonadaptive scenarios of the Ural Owl's life history are discussed.
Validation of the Labeled-Water Method for Estimating Food Consumption in Nestling Herons
Authors: Salatas Johanna H. , Frederick Peter C. , Nagy Kenneth A. , Williams Gary E.
Published: September 2019

Accurate measurements of food consumption by young birds are of great value in a variety of ecological studies, but traditional measurement methods are problematic and prone to high error. In animals that obtain their water primarily through food, it is possible to estimate food consumption from measurements of water influx rate, using radioactively labeled water (3H2O), and diet water content. We evaluated that method by comparing actual food consumption with simultaneous estimates of food consumption based on the labeled-water method in captive-reared nestling Tricolored Herons (Egretta tricolor). There was good agreement. The average error in the isotope method was −2% (SD = 8%), and that difference was not statistically significant. An errors analysis indicated that the accuracy of this method is sensitive to determinations of dietary water content and animal body water content, and to estimates of rates of metabolic water production and unidirectional water vapor input.
Does Egg Rejection Account for the Low Incidence of Cowbird Parasitism in Chestnut-Collared Longspurs (Calcarius Ornatus)?
Authors: Davis S. K. , Klippenstine D. R. , Brigham R. M.
Published: September 2019

We experimentally parasitized Chestnut-collared Longspur (Calcarius ornatus) nests with mimetic and nonmimetic Brown-headed Cowbird (Molothrus ater) eggs to determine whether the low frequency of parasitism reported for that grassland host is due to egg rejection behavior. Longspurs accepted all 23 mimetic eggs (real and wooden) and rejected 9 of 22 blue nonmimetic eggs. Our results suggest longspurs accept cowbird eggs even though they are physically capable of ejecting them from their nest. Thus, the low parasitism frequency reported for that species is not a result of egg rejection behavior, but may be due to antiparasite strategies that reduce their chances of being parasitized (e.g. nest defense behavior).
Primary Sex-Ratio Variation in Two Brood Parasitic Birds: Brown-Headed Cowbird (Molothrus Ater) and Common Cuckoo (Cuculus Canorus)
Authors: Kasumovic Michael M. , Gibbs H. Lisle , Woolfenden Bonnie E. , Sealy Spencer G. , Nakamura Hiroshi
Published: September 2019

We examined primary sex-ratios of two brood parasitic species, Brown-headed Cowbird (Molothrus ater) and the Common Cuckoo (Cuculus canorus), to determine whether there was any evidence of primary sex-ratio manipulation as has been demonstrated in other species of birds. Despite good reasons for why female brood parasites should manipulate the primary sex-ratio of their young, we found a lack of evidence for a bias in the sex-ratio of eggs produced at the population level, with respect to the host species parasitized or time of breeding season, or in terms of the sex ratio of eggs produced by individual females. Thus, this study provides another example in birds of little evidence for sex-ratio variation in relation to environmental factors.
Male Wing-Patch Asymmetry and Aggressive Response to Intruders in the Common Chaffinch (Fringilla Coelebs)
Authors: Jaboński Piotr G. , Matyjasiak Piotr
Published: September 2019

Recent studies reveal that asymmetries of bilateral characteristics may reflect poor condition, serving as an honest indicator of mate quality. We asked whether bilateral asymmetry might also influence behavior during aggressive intrasexual contests. In the Common Chaffinch (Fringilla coelebs), bilateral, white wing patches (epaulettes) are used during aggressive interactions. We recorded responses of males to model intruders placed on territories of focal males, to determine whether their response to asymmetry varied with wing-patch size. When epaulettes were large, models with asymmetric patches elicited more rapid, directed aggression from the territory owners than did models with symmetric patches. We observed no such difference when model intruders had small epaulettes. If asymmetry of epaulettes in chaffinch males indicates poor condition, our results suggest higher costs of aggressive signaling for individuals in poor than good condition.
Subspecific Differentiation and Conservation of Song Sparrows (Melospiza Melodia) in the San Francisco Bay Region Inferred by Microsatellite Loci Analysis
Authors: Chan Yvonne , Arcese Peter
Published: September 2019

We examined genetic population structure of five putative subspecies of Song Sparrows (Melospiza melodia) in the San Francisco Bay region (M. m. samuelis, M. m. maxillaris, M. m. pusillula, M. m. gouldii, and M. m. heermanni) at nine microsatellite loci to assist the development of Song Sparrow conservation and management strategies. We sampled nine populations from five putative subspecies and found low estimates of differentiation between populations within subspecies and between. Despite low estimates of divergence, genetic structure at the subspecies level was indicated by the larger amount of variance accounted for by subspecies than populations. We propose that a management unit encompassing the range of M. m. pusillula be given priority for conservation on the basis of the extent of genetic divergence shown by Cavalli-Sforza and Edward's chord distance, and the topology of an unweighted pair group cluster analysis supported by 100% of bootstrap replicates across loci. Although M. m. samuelis and M. m. maxillaris appear undifferentiated from M. m. heermanni, it remains possible that adaptive differences between those types were not identified with neutral loci.
Effects of Thinning and Herbicide Treatments on Nest-Site Selection by Songbirds in Young Managed Forests
Authors: Easton Wendy E. , Martin Kathy
Published: September 2019

Routine silvicultural practices continue to alter the structure and composition of forests after logging by removing deciduous vegetation from regenerating coniferous forests. We identified nest trees and surveyed vegetation in a 5 m radius surrounding songbird nests (nest patch) and compared the nest patches to available habitat in nine 11–22 year old conifer plantations (22–47 ha) where 90–96% of deciduous stems were removed by two treatments: manual thinning, and manual thinning plus application of glyphosate (herbicide). The control and two treatments were replicated three times. We characterized the nest patches of five species: Warbling Vireo (Vireo gilvus), Dusky Flycatcher (Empidonax oberholseri), Swainson's Thrush (Catharus ustulatus), American Robin (Turdus migratorius), and Chipping Sparrow (Spizella passerina). During three post-treatment years, areas treated with thinning plus herbicide remained depauperate of deciduous vegetation whereas thinned sites experienced deciduous regrowth. Despite variation in the density of deciduous trees and in the type of tree used for nesting in the control and treatments, nest patches were positively correlated with the amount of remaining deciduous vegetation, representing habitat that either escaped or recovered from silvicultural treatments. That relationship was stronger in areas with the fewest deciduous trees. Nests were more likely to be successful in areas with more willow. Within a mosaic of managed forest stands, birds appear to use the same proximate habitat cues for selecting a nest patch despite varying fitness consequences across different silviculture regimes. Although birds appeared to compensate for changes in stand habitat by finding patches of untreated vegetation or altering the type of tree they nested in, there was a reproductive cost for some species.
Social and Genetic Monogamy in Territorial and Loosely Colonial Populations of Phainopepla (Phainopepla Nitens)
Authors: Chu Miyoko , Koenig Walter D. , Godinez Alvaro , McIntosh Carl E. , Fleischer Robert C.
Published: September 2019

We observed courtship and copulatory behavior in two populations of Phainopeplas (Phainopepla nitens) with contrasting social systems and used multilocus DNA fingerprinting to assess rates of extrapair fertilization (EPF). Phainopeplas from both territorial and loosely colonial populations copulated infrequently (≤2 times per day). No extrapair copulations (EPCs) were observed in either population. We found no evidence of EPFs in 48 nestlings from 25 nests. Thus, Phainopeplas appear to be both socially and genetically monogamous. However, Phainopeplas are not monogamous over their lifetimes—they do not retain mates from year to year and appear to switch mates between breeding localities within the same year. Compressed breeding seasons, geographically shifting food resources, and widespread breeding failures may favor monogamy during any given breeding attempt while allowing opportunities to switch mates between breeding localities and years.
Soaring Flight in the Eleonora's Falcon (Falco eleonorae)
Authors: Rosén Mikael , Hedenström Anders
Published: September 2019

Eleonora's Falcon (Falco eleonorae) breeds in the Mediterranean region and is highly adapted for catching small birds on passage migration between Eurasia and their African winter quarters, which they feed their young. We studied gliding flight behavior of Eleonora's Falcon at a breeding colony located on a small island southwest of Sardinia, Italy. Gliding and soaring flight performance was measured using an optical range finder and evaluated against flight mechanical theory. The male falcon does the majority of hunting and usually sets off from the colony to hunting areas located at high altitude over the open sea to catch prey. To lower the cost of transport and maximize the energy gain from hunting, we show that the birds use vertical winds for soaring when available. The occurrence of rising air changes with wind direction. At north-northwesterly winds (on-shore), slope lift is available outside the nesting cliffs, and at south-southeasterly winds thermals that form over the island drift out over the sea. Our observations demonstrated the flexibility of flight behavior in relation to the wind situation, and birds thereby make full use of available soaring conditions.
Did Blue Eggs of Black-billed (Coccyzus erythropthalmus) and Yellow-billed (C. americanus) Cuckoos Evolve to Counter Host Discrimination?
Authors: Lorenzana Janice C. , Sealy Spencer G.
Published: September 2019

Hughes (1997) hypothesized that the blue coloration of Black-billed (Coccyzus erythropthalmus) and Yellow-billed (C. americanus) cuckoo eggs evolved in response to egg discrimination by their hosts. From that hypothesis, we predicted that cuckoo hosts would eject ancestral nonmimetic (white) eggs, but be more likely to accept mimetic (blue) eggs. American Robins (Turdus migratorius) and Gray Catbirds (Dumetella carolinensis) were used to test that hypothesis because they are ejecter species that lay blue eggs and have been parasitized by Coccyzus cuckoos. Hughes' egg-mimicry hypothesis was not supported because robins and catbirds did not significantly eject white cuckoo eggs more frequently than blue cuckoo eggs. Indeed, most robins accepted both egg types. Furthermore, the observational evidence for egg mimicry is not convincing because only 5 of the 15 host species that Hughes (1997) described as having eggs that “fully or nearly match” the egg color of Black-billed and Yellow-billed cuckoos actually do so.
Molt-Migration in Western Tanagers (Piranga Ludoviciana): Age Effects, Aerodynamics, and Conservation Implications
Authors: Butler Luke K. , Donahue Michael G. , Rohwer Sievert
Published: September 2019

We describe timing and location of the prebasic molt in Western Tanagers (Piranga ludoviciana), focusing on age class differences in premolt movements. Most adults migrate south to the American Southwest where they stop to molt before moving on to their wintering grounds. Molting adults are found in southern mountain regions (Sierra Madres and southern Rockies) and in the Mexican monsoon region, where late summer rains cause a substantial increase in productivity. In contrast, juvenile Western Tanagers move to nearby montane habitats to molt before migrating, a previously undocumented strategy in western passerines that show molt-related movements. By molting in nearby montane habitats, juveniles avoid the aerodynamic cost of migrating in their “fluffy”, aerodynamically inefficient juvenal plumage. Western Tanagers are the fifth species known to use the Mexican monsoon region during the prebasic molt, further affirming the importance of that area to the conservation of Neotropical migrants that breed in western North America.
Massive Collapse and Rapid Rebound: Population Dynamics of Eared Grebes (Podiceps nigricollis) During an ENSO Event
Authors: Jehl Joseph R. , Boyd W. Sean , Paul Don S. , Anderson Daniel W.
Published: September 2019

In autumn, >99% of North American Eared Grebes (Podiceps nigricollis) stage at Mono Lake, California, and Great Salt Lake, Utah, creating an exceptional opportunity to measure population trends in a common and otherwise widely distributed species. Aerial photocounts showed that numbers at both lakes fluctuated in parallel, from a total of ∼3.56 million in 1997, then crashing to 1.60 million in 1998. The decline was coincident with a major El Niño, during which hundreds of thousands starved in the Gulf of California. The population rebounded to 3.27 million by 2000, illustrating the species' potentially high survivorship throughout the year. Catastrophic events are evidently the major factors affecting proximate changes in population size. Factors that set the ultimate limit to the population can be clarified through long-term studies at staging areas.
Territoriality and Neighbor Assessment in Brown Jays (Cyanocorax Morio) in Costa Rica
Authors: Hale Amanda M. , Williams Dean A. , Rabenold Kerry N.
Published: September 2019

Defense of group-held resources is a common and widely accepted function of territorial interactions between neighboring groups. In addition, territorial interactions could provide opportunities to assess members of neighboring groups and reproductive opportunities there, or to solidify status in the home group. We studied group-level characteristics and individual participation in territorial encounters in the cooperatively breeding Brown Jay (Cyanocorax morio). Intergroup encounters at stable territory boundaries include both aggressive and affiliative behavior, which suggests that a territorial encounter could function as both a resource defense mechanism and as an arena for social interactions. Territory characteristics that increase the probability of contact between groups (long boundaries, large combined group size, and home range overlap) explain much of the variation in frequency of territorial encounters. Male-biased dispersal was more common to neighboring groups with long boundaries, supporting the idea that frequent interactions between neighbors facilitate dispersal. Females usually inherit breeding positions on their natal territories, and participation in intergroup encounters by females does not vary with age or breeding status. In addition to defending group resources, females on their natal territories could be defending their positions in the breeding queue. Immigrant females are not likely to breed successfully, or to disperse again, and they participated less than expected. Participation by both natal and immigrant males varied by age; young males, at the ages when dispersal and intergroup forays are most likely, participated more than expected, whereas older males (≥4 years) participated less. That is consistent with the hypothesis that participation in intergroup encounters facilitates dispersal and improves integration into social groups. Because extragroup matings occur in this population, both breeding females and males could be assessing neighboring individuals for mating opportunities. Resource defense and social facilitation are not mutually exclusive hypotheses, and our observations suggest that both are important components of territorial encounters in Brown Jays.
Reproduction of Plain Pigeons (Columba Inornata Wetmorei) in East-Central Puerto Rico
Authors: Rivera-Milán Frank F. , Ruiz Carlos A. , Cruz José A. , Sustache José A.
Published: September 2019

The Puerto Rican Plain Pigeon (Columba inornata wetmorei) was listed as endangered in 1970. Transect-survey and nest-monitoring data were collected to estimate reproductive parameters and to assess effects of weather, food, predation, and habitat. We monitored 377 of 423 nests found in east-central Puerto Rico during February-September 1986-2000. The largest sampling effort was conducted in May-June 1998, and 131 nests were found along 8,460 m, resulting in a nest density (D̂) of 5.26 per hectare or 356 nesting pairs (N̂) in the surveyed area (a = 67.7 ha). Nest spatial distribution was highly clumped (b̂ = 3.2) and transect surveys were highly variable (CV = 40%). Thus, 34,000 m needed to be surveyed for a desired coefficient of variation (CV[D̂]) of 20%. Nest density varied widely during May-June 1986–2000. With a CV about the trend line of 121%, from 18 to 28 years of data would be needed to detect an increase or a decrease (r) of 5–10% in log-transformed nest density estimates through linear regression analysis (alpha = 0.15 and power = 0.80). Whereas food abundance had positive and significant relationships with nest density and number of fledglings produced, predator density had negative and significant relationships with nesting success and the number of fledglings produced. Predation accounted for 79% of nest losses (n = 183). Mayfield's estimates of nesting success averaged 40% and an average of 0.5 fledglings were produced per nesting pair. Because Plain Pigeons are able to produce fledglings from three or more broods per year and have extended nesting seasons (with a nest density peak usually occurring in May-June), we hypothesized that hatch-year and after-hatch-year survival rates of 50–65% and a yearly productivity of 1.4–2.0 fledglings per nesting pair were enough to offset mortality. Our optimism is tempered by the fact that Plain Pigeons have not been reported nesting outside east-central Puerto Rico, where rapid destruction and fragmentation of second-growth forests, catastrophic weather, food availability, nest predation, illegal hunting and poaching of nestlings may interact and cause an irreversible population decline. Managers should focus on conserving and restoring second-growth forest fragments to provide food and cover throughout the year. Additional recommendations are given based on the results of our study, which was part of a larger study of factors affecting the reproduction of columbids on Puerto Rico and its territories.
Experimental Test of the Importance of Preen Oil in Rock Doves (Columba Livia)
Authors: Moyer BrettR. , Rock Alex N. , Clayton Dale H.
Published: September 2019

Most species of birds have a uropygial gland, also known as a preen gland, which produces oil that birds spread through their plumage when preening. The plumage of waterfowl deprived of uropygial oil becomes brittle and is subject to breakage. For other groups of birds, however, the importance of preen oil remains unclear. Previous workers have argued that preen oil may serve little or no function in Columbiforms (pigeons and doves). We tested that assertion by removing uropygial glands from Rock Doves (Columba livia) and assessing their plumage condition after several months. The results of that experiment showed significant degradation of plumage in the absence of oil. Our results are the first rigorous demonstration that preen oil is important for plumage condition in nonwaterfowl.

We tested one possible function of preen oil—that it has insecticidal properties and that reduction in plumage condition on birds without glands is due to an increase in ectoparasites. We tested that hypothesis for feather-feeding lice (Phthiraptera:Ischnocera) using both in vitro and in vivo experiments. Lice raised in an incubator died more rapidly on feathers with preen oil than on feathers without oil, which suggests that preen oil may help combat lice. However, removal of the preen gland from captive birds had no significant effect on louse loads over the course of a four-month experiment. Although the results of our in vivo experiments suggest that preen oil may not be an important defense against lice, further experiments are needed. We also consider the possibility that preen oil may protect birds against other plumage-degrading organisms, such as bacteria and fungi.
The Birds of Ecuador, Volume I: Status, Distribution, and Taxonomy. Volume II: Field Guide
Authors: Rowlett John
Published: September 2019

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.
Comparison of Breeding and Postbreeding Movements and Habitat Requirements for the Scarlet Tanager (Piranga Olivacea) in Virginia
Authors: Vega Rivera J. H. , McShea W. J. , Rappole J. H.
Published: September 2019

We investigated movements and habitat use during breeding and postbreeding periods in Scarlet Tanagers (Piranga olivacea) during June-September 1998 in northern Virginia deciduous forest. Nine birds (8 males and 1 female) remained on the same home range during both breeding and postbreeding periods, whereas 11 birds (9 males and 2 females) shifted home range (>300 m) between periods. Breeding season home-range size ranged from 2.6 to 5.6 ha (95% kernel), and core area from 0.61 to 0.93 ha (50% kernel). Postbreeding home ranges were similar in size to home range during the breeding period for birds that remained in the vicinity of nesting areas, but were larger for birds that moved away from the nesting area. Scarlet Tanagers occurred in both mature and successional forest during breeding and postbreeding periods, with some indication of increased use of earlier successional stages during the postbreeding period. Needs for Scarlet Tanagers during the postbreeding period (molt, premigratory fattening) differ from those during the breeding period (pair formation, nest placement, rearing of young). Those differences provide a plausible explanation that all tanagers changed focal areas between breeding and postbreeding periods. These findings confirm the need for taking the postbreeding period into account, both for understanding migrant life history and successful conservation.
Seasonal and Diurnal Body-Mass Fluctuations for two Nonhoarding Species of Parus in Sweden Modeled Using Path Analysis
Authors: Rintamäkt Pekka T. , Stone Jon R. , Lundberg Arne
Published: September 2019

According to the hypothesis that has been invoked most frequently to explain seasonal fattening patterns for birds—the “adaptive winter-fattening hypothesis”—individuals respond to worsening foraging conditions by increasing body mass and energy reserves. Two hypotheses have been proposed equally frequently to explain daily weight gain patterns for birds: according to the “state-dependent foraging hypothesis,” energy reserves should be amassed early during the day, when starvation risk increases; according to the “mass-dependent predation-risk hypothesis,” mass gain should be delayed for as long as possible, to minimize predation risk. Those hypotheses have been tested previously, using statistical methods (e.g. multiple-regression analysis) that assume independence among environmental variables (e.g. photoperiod and temperature). We conducted path analyses that included four predictor variables (day-in-season, hour-in-day, mean daily temperature, and daily precipitation) to model body-mass fluctuations for two small, nonhoarding (noncaching) passerine species that inhabit central eastern Sweden. Data were partitioned hierarchically into species, age class, gender, and season subgroups. As reported in many small passerine species studies, body mass increased during the day and maximized at dusk; over seasons, body mass increased during autumn, maximized by midwinter, and declined toward breeding in spring. Path analysis models accounted for 9.5–49.9% (mean 26.3%) for Blue Tit (Parus caeruleus) body mass variance and 1.8–52.3% (mean 16.8%) for Great Tit (P. major) body mass variance; for both species, accountability was lowest for autumn (Blue Tit,12.2%; Great Tit, 7.3%), highest for winter (Blue Tit, 33.4%; Great Tit, 21.9%), and intermediate for spring (Blue Tit, 22.7%; Great Tit, 11.8%); for Blue Tits, it was greater for adults than for juveniles (33.2 and 21.7%); whereas negligible for Great Tits (15.9 and 17.3%) and slightly greater for males than for females (Blue Tit, 27.4 and 23.5%; Great Tit, 23.1 and 21.3%). Those results are consistent with predictions formulated on the basis of the adaptive winter-fattening, partially with state-dependent foraging, and, possibly, mass-dependent predation-risk hypothesies and reveal that body-mass fluctuations are associated to a greater extent with photoperiod than with temperature.
Beneficial Effects of Cloacal Bacteria on Growth and Fledging Size in Nestling Pied Flycatchers (Ficedula Hypoleuca) in Spain
Authors: Moreno Juan , Briones Víctor , Merino Santiago , Ballesteros Cristina , Sanz Juan J. , Tomás Gustavo
Published: September 2019

Effects of bacteria on avian hosts in the wild have received little attention until recently. Whereas the pathogenic effects of bacteria are well known, positive effects of symbiotic bacteria are more rarely considered. Nestling growth has important repercussions for offspring fitness in avian populations and may be affected by microbial colonization of the gut. Enterococcus faecalis is a common opportunistic pathogen, whereas E. faecium has been used as a growth promoter because it interacts competitively with pathogenic bacteria, E. faecalis included. We followed the growth in tarsus length and mass of 18 Pied Flycatcher (Ficedula hypoleuca) broods. Chicks were weighed and measured on days 4, 8, 10, and 13 after hatching. On day 13, wing length was also measured and cloacal swabs were taken of two chicks in each brood for detection of enterococci. In all, the methods used allowed us to detect six species of bacteria among a possibly much richer community. Most chicks had E. faecalis, whereas E. faecium was less prevalent. There was a negative association between scores for E. faecalis and for the rest of the species pooled. The presence of E. faecalis showed no detectable association with nestling mass or size at any age, whereas the presence of the other species showed significantly positive associations with mass and size on day 13, but not before. Presence of E. faecium on its own was positively associated with nestling mass and size shortly before fledging. E. faecium may act as a growth promoter in the wild through its competitive interactions with facultative pathogenic bacteria. The presence of some microbes are critically important in avian growth and development.
Extrapair Paternity and Breeding Synchrony in Gadwalls (Anas Strepera) in North Dakota
Authors: Peters Jeffrey L. , Brewer Gwenda L. , Bowe L. Michelle
Published: September 2019

Extrapair paternity and its correlates with breeding synchrony were examined in Gadwall (Anas strepera) using microsatellite DNA fingerprinting. Eleven of 261 ducklings (4.2%) within 8 of 29 broods (27.6%) had genotypes consistent with extrapair fertilizations, a comparable frequency to other species of waterfowl for which extrapair paternity has been documented. We found no evidence of intraspecific brood parasitism. The frequency of extrapair paternity was not significantly correlated with breeding synchrony. We suggest that female absences during egg-laying may have provided males with opportunities to pursue extrapair copulation when breeding was synchronous.
Function of Tail Streamers of Red-Tailed Tropicbirds (Phaethon Rubricauda) As Inferred From Patterns of Variation
Authors: Veit Allison C. , Jones Ian L.
Published: September 2019

We investigated the function of Red-tailed Tropicbird (Phaethon rubricauda) tail streamers by quantifying patterns of variation in streamers and other measurable traits on the basis of measurements of 659 individuals, including 422 of known age and 459 of known sex, measured in the field from 2000 to 2002. Our data were consistent with the idea that Red-tailed Tropicbirds' tail streamer ornaments function for mate attraction, but it suggested that variability in streamer expression is arbitrary and unlikely to provide a meaningful signal of individual quality during mate choice. The two elongated red tail streamers are composed of bilaterally symmetrical filamentous central rectrices with a black rachis and narrow red vane averaging 399 ± 1.8 mm (SE) in length when fully grown. Prior to breeding, individuals of opposite sex conspicuously display elongated red tail streamers during complex aerial courtship. Streamers exhibited measurement asymmetries (the difference between new and old fully grown tail streamers) of up to 144 mm because of wear at the tip of the older streamer, which accounts for most of the difference in the lengths of two fully grown streamers in individual birds. As in other putative sexually selected traits, tail streamers were more variable than nonornamental traits across individuals. Males were slightly larger than females in length of fully grown streamers (ratio 1.04), culmen length (ratio 1.02), and tarsal length (ratio 1.01). There was no correlation between fully grown streamer length and body size (score on first principal component) (r = 0.004), wing length (males, r = 0.05; females, r = 0.10), or mass (males, r = 0.10; females, r = 0.04), which is consistent with the hypothesis that streamers have an ornamental rather than aerodynamic function. There was a significant correlation between the ratio of streamer lengths (growing vs. fully grown, r = 0.50) of male and female pair members, indicating that at least the timing of ornament development was coordinated within pairs. However, tail streamers did not appear to be good indicators of an individual's “quality;” on the basis of 372 adults of known age (3–22 years), streamer length did not increase with age (r = 0.30) and was not correlated with an index of body condition (r = 0.03). The streamer length of pair members was not correlated with chick asymptotic body mass or chick fate, nor was female streamer length with egg size.
More Eggs the Better: Egg Formation in Captive Barn Owls (Tyto Alba)
Authors: Durant Joël M. , Massemin Sylvie , Handrich Yves
Published: September 2019

We studied rapid yolk deposition (RYD) in Barn Owls (Tyto alba) on the basis of the analysis of 26 eggs laid by “dye-dosed” captive female Barn Owls in five different broods. Pictures of yolks were examined to assess daily rates of yolk deposition. We used those data in combination with data from the dissection of ovaries of another five breeding females. We found that the total duration between initiation of RYD and laying of the corresponding egg was only 13.6 days, with an interval between yolk completion and oviposition of 2.4 days. The total number of follicles that may have given eggs was found to be 25. That high number of follicles and the short RYD period explain the particularly high reproductive potential of this nocturnal raptor species.
Blood Isotopic (δ13C and δ15N) Turnover and Diet-Tissue Fractionation Factors in Captive Dunlin (Calidris Alpina Pacifica)
Authors: Ogden Lesley J. Evans , Hobson Keith A. , Lank David B.
Published: September 2019

Avian studies are often interpreted using dual (e.g. 13C, 15N) isotope models, assuming turnover of both isotopes occur at similar rates, but only a few studies have quantified turnover rates for more than one of those isotopes simultaneously. To test the generality of previous turnover and fractionation estimates and assumption of synchronous C and N patterns of turnover rates, we captured Dunlin (Calidris alpina pacifica) wintering in the Fraser River Delta, British Columbia, and derived isotopic turnover rates and diet-tissue fractionation factors by experimentally manipulating diet. Birds (n = 15) were initially fed a terrestrially derived diet (mean δ13C: −24.7‰, mean δ15N: 3.5‰) for 54 days. A treatment group (n = 11) was then switched to a marine-derived diet (mean δ13C: −18.3‰, mean δ15N: 13.7‰); a control group (n = 4) was maintained on the terrestrial diet for a further 59 days. An exponential model described patterns of isotopic turnover for 13C and 15N, and turnover rates and half-lives of the two isotopes were correlated, confirming the assumption of synchronous patterns of turnover for those isotopes. The half-lives for 13C and 15N in Dunlin whole blood were 11.2 ± 0.8 days and 10.0 ± 0.6 days, respectively, and are among the lowest values obtained to date for wild birds. Variation in turnover rate among individuals was not related to indices of body condition.
Night Movements of Young Reed Warblers (Acrocephalus Scirpaceus) in Summer: Is it Postfledging Dispersal?
Authors: Mukhin Andrey
Published: September 2019

I studied summer movements of juvenile Reed Warblers (Acrocephalus scirpaceus) marked as nestlings during four field seasons (1999–2002). To control for birds' movements, nocturnal playback of songs and daytime mist-netting were done. Captures by song playback suggest the existence of nocturnal postfledging movements in Reed Warblers. Birds' age (days) during such movements was found to be 39–52 days. I analyze the temporal schedule and physiological condition of the birds during this period and discuss the mechanism of nocturnal postfledging dispersal and its background and relationships with other events of the annual cycle during the premigratory period.
Habitat Requirements and Selection by Kelp Gulls (Larus Dominicanus) in Central and Northern Patagonia, Argentina
Authors: Borboroglu Pablo García , Yorio Pablo
Published: September 2019

We analyzed habitat requirements and selection of Kelp Gulls (Larus dominicanus) breeding at 68 colonies along 2,500 km of coastline in Patagonia, Argentina. Kelp Gulls use a wide range of nesting habitats that include areas with shrub, grass, and herbs which provide different degrees of cover; open ground of various substrate types; and slopes of widely different gradients, confirming the plasticity of the species with respect to habitat recorded elsewhere in the Southern Hemisphere. Eighty percent of the colonies were on islands, the probability of occupation of which increased with distance from mainland and availability of vegetation. Vegetation cover was a key component of nesting habitat for Kelp Gulls in Argentina. Gulls occupied areas with higher cover than random areas; but within vegetated areas, they showed preference for sparser cover that increased visibility and facilitated escape. Kelp Gulls often nested with other species of seabirds and seals and had a positive association with the Olrog's Gull (L. atlanticus).
A Red Bird in a Brown Bag: The Function and Evolution of Colorful Plumage in the House Finch.
Authors: Andersson Staffan
Published: September 2019

The following critiques express the opinions of the individual evaluators regarding the strengths, weaknesses, and value of the books they review. As such, the appraisals are subjective assessments and do not necessarily reflect the opinions of the editors or any official policy of the American Ornithologists' Union.
Structure and Organization of Canopy Bird Assemblages in Central Amazonia
Authors: Naka Luciano Nicolás
Published: September 2019

I analyzed the species composition, structure, and trophic organization of bird assemblages in the forest canopy around Manaus, Brazil. Using three canopy towers located in primary terra firme forests, I conducted 117 censuses over a 13 month period, recording 160 bird species. The three study sites had similar species richness (between 126 and 128 species), sharing 95 species in common, which accounted for >90% of all individual records. Most species recorded in the canopy (110) belonged to the core canopy avifauna. The other 50 species included migrants (13), species that feed overhead (8), species from lower strata (15), night birds (3), and vagrants or visitors from open areas and second-growth forests (11). Most of those species, however, appeared in very low numbers in the forest canopy, except understory frugivores, which regularly fed on canopy fruits. Among the migratory species were some Nearctic (6), Austral (3), and species probably holding both migratory and resident populations in the area (4). Additionally, I found evidence that two species of parrots perform seasonal movements, leaving the forest canopy around Manaus during the dry season. Frugivores dominated the canopy avifauna in abundance, but contradicting results reported from other Neotropical forest canopies, insectivores and frugivores had equal species richness. The canopy avifauna was highly homogeneous among sites in terms of species richness, distribution among abundance classes, and number of species in each feeding guild, habitat, and microhabitat. As in Costa Rica, the canopy avifauna of Manaus was mostly composed by typical canopy bird species, and not by edge-living species as reported from Panama. I suggest that habitat fragmentation may affect the bird community composition in the forest canopy, allowing a higher influx of opportunistic species.
Natural Variation in Flight Performance is Related to Timing of Breeding in Tree Swallows (Tachycineta Bicolor) in New York
Authors: Bowlin Melissa S. , Winkler David W.
Published: September 2019

In many avian species, including Tree Swallows (Tachycineta bicolor), females that lay eggs earlier in the season have higher fitness. It has been hypothesized that nonheritable variation in individual quality could explain how variation in laying date persists in the face of this apparently directional selection. Previous experimental work on Tree Swallows has suggested that natural variation in flight ability enables early-laying females to attain feeding rates high enough to support egg production on earlier, sparser food than later-laying females. We tested that hypothesis with standardized flights through a 9.75-m flight-performance test tunnel. One group of female swallows was tested at the height of the breeding season on 28 May regardless of their nesting phenology; another group was tested on the 11th day of incubation. Average acceleration in the tunnel was negatively correlated with clutch initiation date for the females tested on 28 May. Daily variation in ambient environmental conditions had strong effects on swallow flight performance in the tunnel, and no relationship was observed in the day-11 birds. Because natural variation in foraging performance is correlated with variation in female Tree Swallows' clutch initiation dates, flight ability appears to be a key element of individual quality in this species.
Size Dimorphism, Intrasexual Competition, and Sexual Selection in Wattled Jacana (Jacana Jacana), A Sex-Role-Reversed Shorebird in Panama
Authors: Emlen Stephen T. , Wrege Peter H.
Published: September 2019

We studied sexual size dimorphism, intrasexual competition, and sexual selection in an individually marked population of Wattled Jacanas (Jacana jacana) in the Republic of Panama. Males are the sole incubators of eggs (28-day incubation) and primary providers of chick care (50–60 days). Females were 48% heavier than, and behaviorally dominant over, males. Females also showed greater development of secondary sexual characters (fleshy facial ornamentation and wing spurs) than males. Both sexes defended territories throughout the year against same-sex conspecifics. Competition for territorial space was intense, and many individuals of both sexes did not become breeders. Resident females further competed with one another to accumulate multiple mates, resulting in a mating system of simultaneous polyandry. Female and male residents (territory holders) were larger, heavier, and more ornamented than adult floaters of the same sex. Larger and heavier females also had more mates than smaller females. Body size was thus a critical predictor of success in intrasexual competition for territories (both sexes) and for mates (females). Three measures of sexual selection—(1) sex difference in the opportunity for sexual selection, (2) female-to-male ratio of potential reproductive rates, and (3) operational sex ratio—each indicated that sexual selection is currently operating more strongly on females than on males (female-to-male ratios ranged from 1.43:1 to 2.22:1). Values of 1.61:1 and 1.43:1 represent the first published quantitative estimates of the opportunity for sexual selection for any sex-role-reversed bird. Our study supports the theory that when increased parental care entails reduced opportunities for future reproduction, asymmetries in parental care behaviors of the sexes can influence the intensity of competition for mates and the direction and strength of sexual selection.