bluuebunny/crossref_metadata_2025_split huggingface dataset:
Drought Stress Impairs Communication Between Solanum tuberosum (Solanales: Solanaceae) and Subterranean Biological Control Agents
Authors: Hassani-Kakhki Mahnaz , Karimi Javad , El Borai Fahim , Killiny Nabil , Hosseini Mojtaba , Stelinski Lukasz L , Duncan Larry 
Published: September 2019

Abstract
The attraction of entomopathogenic nematodes (EPNs) to herbivore-injured plant roots has been documented recently to be a common tritrophic interaction. Belowground tritrophic interactions are especially subject to modulation by many abiotic factors including drought. In this study, complementary greenhouse experiments were conducted to understand how drought stress might affect a potato plant’s impact on EPN behavior. In separate trials, the responses of the EPN Steinernema diaprepesi (Nguyen and Duncan) (Rhabditida: Steinernematidae) to root herbivory by larvae of the weevil Diaprepes abbreviatus (Linnaeus) (Coleoptera: Curculionidae), in well-watered and drought stressed potato plants, were measured using soil-matrix olfactometers with two arms. The drought treatments were initiated in 30-d old plants. Drought-stressed potato plants received water when potentiometers read approximately 20 kPa, while for well-watered plants, the number was 8 kPa. Four weeks after initiating the treatments, 400 ml water was added to all pots, immediately before starting the experiments. The experiments revealed that S. diaprepesi infective juveniles (IJs) did not migrate preferentially toward drought-stressed or well-watered plants when neither were subjected to herbivory [t(21) = 1.13, P = 0.269]. However, plants with roots damaged by herbivory attracted more S. diaprepesi IJs if they were well watered than if they were drought stressed [t(24) = 3.19, P = 0.004]. If both plants in the olfactometers were drought stressed, EPNs moved preferentially toward those with root herbivory than those with undamaged roots [t(23) = 3.19, P = 0.004]. No difference was detected in gas chromatography profiles between droughted and well-watered plant roots subjected to herbivory [F(24, 336) = 0.68, P = 0.87]. GC analysis showed that three compounds, including 3-nonanone [t(6) = 4.83, P = 0.003], artemisyl ketone [t(7) = 6.21, P = 0.000], and benzoic acid, 4-ethoxy-, ethyl ester [t(7) = −4.22, P = 0.004] were significantly higher in drought stressed than control plant roots. These results indicate that potatoes, like other plants, can recruit EPNs in response to root herbivory, and that drought stress dampens this tritrophic interaction where choice is involved. Additional research that resolves the mechanisms of these interactions may provide insights to exploit EPNs for crop protection.
Invited Commentary: Making Causal Inference More Social and (Social) Epidemiology More Causal
Authors: Jackson John W , Arah Onyebuchi A 
Published: September 2019

Abstract
A society’s social structure and the interactions of its members determine when key drivers of health occur, for how long they last, and how they operate. Yet, it has been unclear whether causal inference methods can help us find meaningful interventions on these fundamental social drivers of health. Galea and Hernán propose we place hypothetical interventions on a spectrum and estimate their effects by emulating trials, either through individual-level data analysis or systems science modeling (Am J Epidemiol. 2020;189(3):167–170). In this commentary, by way of example in health disparities research, we probe this “closer engagement of social epidemiology with formal causal inference approaches.” The formidable, but not insurmountable, tensions call for causal reasoning and effect estimation in social epidemiology that should always be enveloped by a thorough understanding of how systems and the social exposome shape risk factor and health distributions. We argue that one way toward progress is a true partnership of social epidemiology and causal inference with bilateral feedback aimed at integrating social epidemiologic theory, causal identification and modeling methods, systems thinking, and improved study design and data. To produce consequential work, we must make social epidemiology more causal and causal inference more social.
Temporal and Spatial Patterns in Daily Mass Gain of Magnolia Warblers During Migratory Stopover
Authors: Dunn Erica H. , Moore F. R. 
Published: September 2019

AbstractWhether or not migrants gain mass at a stopover site is an index of site quality. Previous studies have examined mass gain of recaptured birds, and of short-term stopovers by regressing mass at first capture on hour of day. I developed an extension of the latter method using multiple regression to examine the effects on mass gain of hour of day, date, and year. I then used the method to compare the quality of three stopover sites at Long Point, Ontario, for Magnolia Warblers (Dendroica magnolia). At the peak of fall migration, warblers at all three sites gained sufficient mass for a net gain over 24 h, but they gained mass at only two of three sites during spring. Mass gain varied significantly over the course of the day, by date in the season, and among years. The earliest spring migrants lost mass at all sites, but rate of mass gain increased as the season progressed. Similar information for many more species and stopover sites might aid in habitat conservation for migrants.
Blue-Throated Hummingbird Song: A Pinnacle of Nonoscine Vocalizations
Authors: Sigler Ficken Millicent , Rusch Kathryn M. , Taylor Sandra J. , Powers Donald R. 
Published: September 2019

Abstract
Little is known about the structure and function of hummingbird vocalizations. We studied the vocalizations of Blue-throated Hummingbirds (Lampornis clemenciae) at two sites in southeastern Arizona. Songs were produced by males and females. Male songs consisted of arrays of notes organized in clusters of “song units.” Within sites, all males shared the same song units. Individual differences occurred in some temporal aspects of song, and slight but consistent differences in note structure occurred between the two sites. The organization of units within songs was marked by rigid syntax, and long songs were produced by agglutination of units. Male songs may function in territorial advertisement and mate attraction. Female songs were very different acoustically from those of males and typically were given when females were within a few centimeters of a male. In these situations, the female's song often overlapped temporally with the male's song. Of the hummingbird species studied so far, the Blue-throated Hummingbird has the most complex songs and is the only known species with complex female songs. Blue-throated Hummingbirds show convergence with oscines in vocal complexity, song organization, song function, and possible learning of some song elements.
Predation Rates on Real and Artificial Nests of Grassland Birds
Authors: Davison William B. , Bollinger Eric 
Published: September 2019

AbstractWe estimated nesting success at real and artificial nests of grassland birds to test the influence of nest type, nest position, and egg size on predation rates. We distributed wicker nests and realistic woven-grass nests baited with a clay egg and either a Northern Bobwhite (Colinus virginianus) egg or a House Sparrow (Passer domesticus) egg in four grasslands that were part of the Conservation Reserve Program in east-central Illinois. Nesting success averaged 86.5% for 12 days of exposure for artificial nests. For real nests, nesting success was markedly lower, averaging 39% over the entire nesting cycle and 59% during approximately 12 days of incubation. Wicker nests were depredated more often than woven-grass artificial nests (18% vs. 8%), and nests baited with House Sparrow eggs were depredated more often than nests baited with Northern Bobwhite eggs (22% vs. 9%). Elevated and ground nests were depredated at the same rate. Patterns of nest predation on wicker nests were markedly different from depredation patterns on real nests over time and among fields. In contrast, patterns of nest predation on realistic woven-grass nests corresponded much more closely with predation rates of real nests over time and among fields. We suggest that future artificial nest studies use nests and eggs that mimic as closely as possible the real nests and eggs of target species. Use of unrealistic artificial nests and eggs, at least in grasslands, may result in patterns of predation that do not accurately reflect those of real nests. Artificial nests of any type appear to underestimate predation rates on nests of grassland birds, possibly because of a lack of snake predation on artificial nests.
Effect of Ephemeral Food Restriction on Growth of House Sparrows
Authors: Lepczyk Christopher A. , Karasov William H. 
Published: September 2019

AbstractWe tested for the presence of compensatory growth (i.e. faster age-specific growth) following ephemeral periods of food restriction in altricial nestlings using the House Sparrow (Passer domesticus) as a model species. To simulate periods of poor food conditions, we raised nestlings in captivity, fed them a synthetic diet, and held them at constant body mass for 48 h beginning on either day 3 or 6 of life. Controls were fed according to an age-specific feeding schedule that yielded normal growth curves. During realimentation, restricted nestlings did not achieve a faster rate of growth than that of controls. Instead, these nestlings either died (all controls lived) or gained mass at a rate similar to that of controls. Consequently, restricted nestlings reached asymptotic mass two days later than control nestlings. Growth of culmen and tarsus was not affected, but growth of the eighth primary was reduced for several days in nestlings restricted at day 6 (i.e. late restricted), although this difference disappeared by the age of fledging. Because surviving nestlings achieved only a 15.9% increase in food consumption compared with unrestricted controls and were unable to translate it into a faster rate of growth, the nestlings may have been growing at a maximum rate. We found no differences between late-restricted and unrestricted nestlings in % water, % protein, % lipid, and % ash. The two groups were of similar maturity as measured by % body water and the water index. Our results are consistent with current theory in that periods of food restriction delayed the schedule of mass accretion by the length of the restriction period. Although House Sparrows have a labile growth rate and developmental time, our results did not support the hypothesis of compensatory growth. Based on this and one other study, compensatory growth does not appear to occur in altricial birds.
Predicting Migratory Flight Altitudes by Physiological Migration Models
Authors: Liechti Felix , Klaassen Marcel , Bruderer Bruno 
Published: September 2019

AbstractUsing the altitudinal profiles of wind, temperature, pressure, and humidity in three flight models, we tried to explain the altitudinal distributions of nocturnal migrants recorded by radar above a desert in southern Israel. In the simplest model, only the tailwind component was used as a predictor of the most preferred flight altitude (T model). The energy model (E model) predicted flight ranges according to mechanical power consumption in flapping flight depending on air density and wind conditions, assuming optimal adjustment of airspeed and compensation of crosswinds, and including the influence of mass loss during flight. The energy-water model (EW model) used the same assumptions and parameters as the E model but also included restrictions caused by dehydration. Because wind was by far the most important factor governing altitudinal distribution of nocturnal migrants, differences in predictions of the three models were small. In a first approach, the EW model performed slightly better than the E model, and both performed slightly better than the T model. Differences were most pronounced in spring, when migrants should fly high according to wind conditions, but when climbing and descending they must cross lower altitudes where conditions are better with respect to dehydration. A simplified energy model (Es model) that omits the effect of air density on flight costs explained the same amount of variance in flight altitude as the more complicated E and EW models. By omitting the effect of air density, the Es model predicted lower flight altitudes and thus compensated for factors that generally bias height distributions downward but are not considered in the models (i.e. climb and descent through lower air layers, cost of ascent, and decrease of oxygen partial pressure with altitude). Our results confirm that wind profiles, and thus energy rather than water limitations, govern the altitudinal distribution of nocturnal migrants, even under the extreme humidity and temperature conditions in the trade wind zone.
Song Types and Variation in Insular Populations of Lincoln's Sparrow (Melospiza Lincolnii), and Comparisons With Other Melospiza
Authors: Cicero Carla , Benowitz-Fredericks Morgan 
Published: September 2019

AbstractIn contrast to the Swamp Sparrow (Melospiza georgiana) and Song Sparrow (M. melodia), vocal studies of the congeneric Lincoln's Sparrow (M. lincolnii) are essentially lacking. To provide comparative data on song variation in this species, we obtained and analyzed recordings from 58 males (4,537 songs) breeding in montane meadows of the Sierra Nevada and San Bernardino Mountains, California. Males sang from one to six song types, and repertoire size averaged 3.7 types. No two males shared an identical song type. Males varied their types by changing the number of repetitions of a syllable or by adding, deleting, or substituting one or more syllables (i.e. by changing syllable composition). The number of variants, identified on the basis of differences in syllable composition, averaged 2.6 per song type (range 1 to 12). Individual variability was highest in the terminal elements of the song. Production of variants appears to be a process of “open-ended improvisation” of song types. Similarity of songs on the basis of shared syllables, as calculated by simple matching coefficients, showed a strong pattern of concordance with geography. Pairwise similarity declined with increasing distance between meadows, and meadows from different geographic regions clustered separately in a UPGMA tree. Patterns of geographic variation in song of Lincoln's Sparrows are similar to those observed in Song Sparrows and Swamp Sparrows. Song complexity and repertoire size show different evolutionary trends within Melospiza.
Reproductive Consequences of Autumnal Singing in Black Redstarts (Phoenicurus Ochruros)
Authors: Weggler Martin 
Published: September 2019

AbstractIn a migratory population of Black Redstarts (Phoenicurus ochruros) in central Europe, males were territorial and sang in autumn between the end of molt in early September and the abandonment of territories in October. Participants in autumn singing were adult males past their first potential breeding season; subadults rarely defended territories in autumn. Prior to the autumn singing period, unmated males and males after their first breeding season often dispersed to new locations within the study site. Pair associations with experienced female breeders still present on the breeding ground were preformed. Low winter mortality, site dominance, and fidelity to autumn territories allowed the reformation of 59% of autumnal pair bonds in the following spring. The mating pattern was assortative by age because the initiation of territory acquisition and pair formation was temporally segregated by more than six months between subadult and adult breeders. Males benefitted from mating with experienced females because they started breeding earlier and initiated more breeding attempts per season. Autumnal singing and territoriality, a phenomenon that has not attracted much attention, may play a key role in the understanding of age-related reproductive asymmetries in Black Redstarts. Age-related reproductive performance may be the underlying cause for the evolution of delayed plumage maturation in this species.
Reproductive Anatomy and Indices of Quality in Male Tree Swallows: The Potential Reproductive Role of Floaters
Authors: Peer Katharina , Robertson Raleigh J. , Kempenaers Bart 
Published: September 2019

AbstractAvian populations often consist of breeding residents and nonbreeding floaters. It is usually assumed that floaters are lower-quality individuals that do not reproduce, but floater tactics and potential reproductive success have rarely been examined carefully. To assess the potential reproductive role of male floaters in Tree Swallows (Tachycineta bicolor), we compared their reproductive organs and morphology with those of resident males. Tree Swallows show high levels of extrapair paternity, but two studies attempting to find the fathers of the extrapair offspring have been remarkably unsuccessful. Floater males that father extrapair young would face intense sperm competition. Theory predicts that under intense sperm competition, selection favors males that produce more sperm. Comparative studies in birds and other taxa provide evidence that the level of sperm competition influences relative testes size and sperm production. However, intraspecific adaptations to different levels of sperm competition have received far less attention. Floater Tree Swallows did not differ from resident males in any of the characters we measured, including testes size, but floaters had significantly larger cloacal protuberances. Thus, our results do not confirm the general assumption that floaters are lower-quality individuals that do not reproduce. Furthermore, floaters showed high variation in the volume of the cloacal protuberance (reflecting sperm numbers), which suggests that they engage in copulations. We conclude that floater male Tree Swallows invest heavily in sperm production (as do resident males) to exploit breeding opportunities through takeovers or extrapair copulations.
Adult Prey Choice Affects Chick Growth and Reproductive Success in Pigeon Guillemots
Authors: Golet Gregory H. , Kuletz Katherine J. , Roby Daniel D. , Irons David B. 
Published: September 2019

AbstractPigeon Guillemots (Cepphus columba) are diving seabirds that forage near shore and feed their chicks demersal and schooling fishes. During nine years between 1979 and 1997, we studied chick diet, chick growth rate, and reproductive success of Pigeon Guillemots at Prince William Sound, Alaska, to determine factors limiting breeding populations. We found evidence for prey specialization among breeding pairs and detected differences in reproductive success between specialists and generalists. Pairs that specialized on particular prey types when foraging for their chicks fledged more chicks than those that generalized, apparently because they delivered larger individual prey items. Reproductive performance also varied among guillemot pairs as a function of the proportion of high-lipid schooling fishes fed to the chicks. Pairs that delivered primarily high-lipid fishes (Pacific sand lance [Ammodytes hexapterus] and Pacific herring [Clupea pallasii]) had higher overall reproductive success than pairs that delivered primarily low-lipid demersal fishes (e.g. sculpins, blennies, stichaeids, and pholidids) and gadids. The proportion of high-lipid fishes in the diet was positively related to chick growth, suggesting that piscivorous seabird chicks benefit from eating species with high-energy densities during development. The diet of Pigeon Guillemot chicks showed high annual variation from 1979 to 1997, presumably because of fluctuations in abundance of Pacific sand lance, a high-lipid schooling fish. Regression analyses suggest that the percent occurrence of high-lipid fishes in the diet affected chick growth rate at the population level. We conclude that Pigeon Guillemots benefit by specializing when selecting prey for their chicks, and that high-lipid schooling fishes enhance chick growth and reproductive success.
A New Bush-Warbler (Sylviidae, Bradypterus) From Taiwan
Authors: Rasmussen Pamela C. , Round Philip D. , Dickinson Edward C. , Rozendaal F. G. 
Published: September 2019

Abstract
A bush-warbler of the genus Bradypterus, known from the mountains of Taiwan since 1917, has never been formally named as a distinct taxon. Songs of the Taiwan population differ strikingly from those of its Asian congeners in being much clearer, sweeter, more piercing, and in having a very different structure of elements. Several subtle but consistent morphological differences exist between specimens from Taiwan and all named taxa, principally in bill size and shape, plumage color and reduced variability, pattern of undertail coverts, and wing formula. Therefore, the Taiwan population is best treated as a new species.
A Critical Evaluation of Kenyon's Shag (Phalacrocorax [Stictocarbo] Kenyoni)
Authors: Rohwer Sievert , Filardi Christopher E. , Bostwick Kimberly S. , Peterson A. Townsend 
Published: September 2019

Abstract
We examine the validity of Phalacrocorax [Stictocarbo] kenyoni, which was described by Siegel-Causey (1991) from the Aleutian Islands using midden remains and existing skeletal specimens. We emphasize a morphometric evaluation of the taxon using 224 skeletal specimens of North Pacific cormorants, but we also evaluate the qualitative characters originally used to characterize P. kenyoni. Principal components and discriminant function analyses of 14 skeletal characters failed to support the validity of the species. Similarly, all seven of the character states that Seigel-Causey described as unique to P. kenyoni also were found in P. pelagicus and P. urile. Thus, the three type specimens of P. kenyoni appear to be P. pelagicus. Although we could not confirm the validity of P. kenyoni, our morphometric analyses revealed that P. pelagicus individuals from the central Aleutians are smaller than those from surrounding populations.