1,720,969 research outputs found
Physiological conditions predict nocturnal restlessness at a stopover site in wild migratory passerines
No full textPhysiological control of nocturnal migration
No full textProgramma Vigoni
Collaborazione Italia-Germania 2011-2012
Nocturnally migratory birds interrupt migration temporarily if they have depleted energy reserves and find suitable ‘refuelling’ sites. Besides weather conditions, a major determinant of whether a bird rests or continues migration is body fat. We are interested in understanding which physiological mechanisms switch on and off nocturnal migration during and after refuelling at a stop-over site. We have identified a candidate hormone, ghrelin, that may be a major player in influencing decisions to migrate or not. The aim of this project is to substantiate (or disprove) the evidence for the role of ghrelin in the regulation of migratory behavior
Body fat influences departure from stopover sites in migratory birds: Evidence from whole-island telemetry
No full textMigration remains one of the great mysteries of animal life. Small migratory birds rely on refuelling stopovers after crossing ecological barriers such as deserts or seas. Previous studies have suggested that fuel reserves may determine stopover duration but this hypothesis could not be tested because of methodological limitations. Here, we provide evidence that subcutaneous fat stores determine stopover duration by measuring the permanence of migratory garden warblers (Sylvia borin) on a small Mediterranean island during spring migration with telemetry methods. Garden warblers with large amounts of fat stores departed the island significantly sooner than lean birds. All except one fat bird left the island on the same evening after capture, with a mean total stopover estimate of 8.8 hours. In contrast, the mean estimated total stopover duration of lean birds was 41.3 hours. To our knowledge, this is the first study that measures the true minimum stopover duration of a songbird during migration. © 2010 The Royal Society
Difficulties and special issues associated with field research in behavioral neuroendocrinology
No full textClassical behavioral neuroendocrinology has focused on a limited number of domestic mammals and birds. The model systems used in these studies represent a very small proportion of the diversity of hormone-behavior interactions found in nature. In the last three decades, an increasing number of researchers have concentrated their efforts on studying behavioral neuroendocrinology of wild animals. Field behavioral neuroendocrinology presents a series of challenges ranging from the design of the experiments to sample preservation and transportation. The constraints of field conditions limit the number of factors that can be controlled for and the questions that can be addressed. On the other side, many behaviors can be studied only in the field, and only a few species can be kept in captivity. Thus, field studies are necessary to understand the complexity and variety of interactions between hormones, brain, and behavior. In this article, we will review some of the peculiarities and challenges of field behavioral neuroendocrinology, including solutions for some of the most commonly encountered technical issues. (c) 2005 Elsevier Inc. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Stopover decision during migration: physiological conditions predict nocturnal restlessness in wild passerines
No full textDuring migration, a number of bird species rely on stopover sites for resting and feeding before and after crossing ecological barriers such as deserts or seas. The duration of a stopover depends on the combined effects of environmental factors, endogenous programmes and physiological conditions. Previous studies indicated that lean birds prolong their refuelling stopover compared with fat birds; however, the quantitative relationship between physiological conditions and stopover behaviour has not been studied yet. Here, we tested in a large sample of free-living birds of three European passerines (whinchats, Saxicola rubetra, garden warblers, Sylvia borin and whitethroats, Sylvia communis) whether the amount of migratory restlessness (Zugunruhe) shown at a stopover site depends on physiological conditions. An integrated measure of condition based on body mass, amount of subcutaneous fat and thickness of pectoral muscles strongly predicted the intensity of Zugunruhe shown in recording cages in the night following capture. These results provide novel and robust quantitative evidence in support of the hypothesis that the amount of energy reserves plays a major role in determining the stopover duration in migratory birds
Variations on the Author
Full text link“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
Full text linkWe 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
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