1,720,965 research outputs found
Flight performance of migrating juvenile barn swallows in relation to fat load and wing aerodynamics
No full textMigratory birds have evolved the ability to accumulate, at appropriate times during the annual life-cycle, large amounts of fat to fuel their migratory journeys. However, increased fuel load leads to an increased body mass, which is expected to make small migratory birds less agile and more vulnerable to predation. Predation risk depends on body mass through its influence on flight performance (flight velocity and acceleration) and especially flight manoeuvrability, traits that are vital in the escape response. In addition, individuals vary in wing aerodynamic properties, which are also expected to affect manoeuvrability and flight performance. We investigated the effects of interindividual variation in fat load and wing aerodynamic traits (wing pointedness, convexity and aspect ratio) on short-term flight performance in 43 juvenile barn swallows (Hirundo rustica) during autumn migration. Individuals were captured at two roosting sites located near Warsaw (Poland) in September 2014. The evaluation of short-term flight performance (maximum velocity and acceleration) and flight manoeuvrability was performed using flight tunnels. Information about fat load was collected using a TOBEC body scanner. Controlling for wing aerodynamic traits, we found that fat individuals reached higher velocity compared to lean ones. On the other hand, controlling for fat load, wing pointedness positively predicted maximum velocity, and negatively predicted the time needed to reach the maximum acceleration. Conversely, fat load or wing aerodynamic traits did not predict flight manoeuvrability. The higher flight velocity reached by birds with larger fat load is in line with the expectations, since comparative evidence suggests that heavier birds can reach higher fly speed than lighter ones. In fact, according to fundamental aerodynamics, the lift force generated on a wing is positively related to flight velocity, and therefore a faster flight is required to hold up more mass. Moreover, by optimizing wingtip vortices, more pointed wings decrease the induced drag and thus could improve flight performance both in terms of speed and acceleration. The lack of any association between fat load and flight maneuverability was against the expectations. In fact, we predicted that birds could trade-off manoeuvrability with fat load. However, experiments were carried out in the initial stages of migration, and none of the individual we tested showed the highest fuel loads that can be observed in this species. This finding suggests that on the initial stages of the migratory journey, when birds start to accumulate fat, they may optimize fuel load in order not to negatively impact on flight performance. However, a trade-off between fuel load and manoeuvrability may be expected to emerge before large ecological barriers that must be crossed with sustained flights, such as deserts and sea, where swallows show the highest fuel load
Flight performance of migrating juvenile barn swallows in relation to fat load and wing aerodynamics
No full textDuring Zugunruhen birds accumulate fat reserves that make them less agile and more vulnerable to predation, through effects on flight performance. We investigated the influence of variations of fat load and wing morphology on flight performance (velocity, acceleration and manoeuvrability) in migrating juvenile barn swallows (Hirundo rustica). Our results show, respectively, controlling for wing shape and fat load, that fat individuals and birds with more pointed wings preformed high-velocity flights. According to aerodynamics, fast flights are required to hold up huge body masses while pointed wings decrease drag and improve velocity. No manoeuvrability and fat load trade-off emerges in this study: birds probably optimize fat reserves in order to not negatively impact on flight abilities; this trade-off may emerge close to ecological barriers, where largest energy resources are crucially required
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Candidate genes have sex-specific effects on timing of spring migration and moult speed in a long-distance migratory bird
Get PDFThe timing of major life-history events, such as migration and moult, is set by endogenous circadian and circannual clocks, that have been well characterized at the molecular level. Conversely, the genetic sources of variation in phenology and in other behavioral traits have been sparsely addressed. It has been proposed that inter-individual variability in the timing of seasonal events may arise from allelic polymorphism at phenological candidate genes involved in the signaling cascade of the endogenous clocks. In this study of a long-distance migratory passerine bird, the willow warbler Phylloscopus trochilus, we investigated whether allelic variation at 5 polymorphic loci of 4 candidate genes (Adcyap1, Clock, Creb1, and Npas2), predicted 2 major components of the annual schedule, namely timing of spring migration across the central Mediterranean sea and moult speed, the latter gauged from ptilochronological analyses of tail feathers moulted in the African winter quarters. We identified a novel Clock gene locus (Clock region 3) showing polyQ polymorphism, which was however not significantly associated with any phenotypic trait. Npas2 allele size predicted male (but not female) spring migration date, with males bearing longer alleles migrating significantly earlier than those bearing shorter alleles. Creb1 allele size significantly predicted male (but not female) moult speed, longer alleles being associated with faster moult. All other genotype–phenotype associations were statistically non-significant. These findings provide new evidence for a role of candidate genes in modulating the phenology of different circannual activities in long-distance migratory birds, and for the occurrence of sex-specific candidate gene effects
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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