1,720,974 research outputs found
Always together: mate guarding or predator avoidance as determinants of group cohesion in white-breasted mesites?
No full textBeing a member of a cohesive group can have fitness benefits such as decreased predation risk, increased feeding efficiency as well as enhanced access to social information and mates. However, competition and the risk of parasite transmission exert centrifugal forces on group-living. Thus, the actual degree of cohesion is expected to vary as a function of the relative importance of several social and ecological factors. White-breasted mesites Mesitornis variegata are medium-sized ground-dwelling birds endemic to the dry deciduous forests of western Madagascar. They live in stable breeding pairs or small family groups, mate monogamously and often form temporary heterospecific associations with canopy-dwelling bird species that give alarm calls to which mesites respond with anti-predator behaviours. We investigated the potential effects of predation risk and mate defence on mesite group cohesion by analysing inter-individual distances of 20 groups as a function of mesite social organization, alarm call events, the size of associated heterospecific flocks, and the adults' reproductive state. Mesite social units were very cohesive, particularly in families, when associated with smaller heterospecific flocks, and after an alarm call event. Adult reproductive state did not influence breeding partners' cohesion. Therefore, the pronounced group cohesion in mesites seems to be mainly a response to the high predation risk typically associated with a terrestrial life-style, and not to mate-guarding. However, we suggest that high group cohesion due to predation risk could limit opportunities for solitary extra-territorial forays to obtain extra-pair copulations, thereby contributing to a strictly monogamous system in this species
Slow development of foraging skills and parental costs of family-living in a semi-precocial, non-cooperatively breeding bird
No full textFamily-living has been recognized as a first step in the evolution of cooperative breeding. Although delayed juvenile dispersal occurs in non-cooperative breeders, studies investigating family formation in these species are rare. Juveniles delay natal dispersal in response to ecological constraints of dispersal and/or benefits of philopatry, with parents predicted to adjust their tolerance towards independent offspring according to their direct fitness benefits. Consequently, precocial chick development is often associated with low parental care and short family association. White-breasted mesites (Mesitornis variegata) are group-living but non-cooperatively breeding birds that live in saturated habitats, whose semi-precocial young exhibit large variation in the timing of natal dispersal. We investigated whether the development of foraging skills of nutritionally independent juvenile mesites affects their dispersal decisions. Additionally, because parents show aggression towards older offspring particularly around the subsequent breeding season, we studied whether family-living is costly for parents. Our results indicate that juveniles develop their foraging skills slowly, that juveniles with poorer foraging skills tend to disperse later, and that adults experience foraging and reproductive costs from extended juvenile association. Therefore, it may be beneficial for less skilled juveniles to remain longer in the safety of the family when breeding vacancies are scarce. Furthermore, parental costs of family-living may trigger parental aggression towards juveniles, resulting in the dissolution of families and the lack of cooperative breeding in this species. This study highlights the importance of cost-benefit analyses from both the parents’ and offspring’s perspective to understand family stability and, hence, evolutionary routes towards cooperative breeding
Delayed juvenile dispersal and monogamy, but no cooperative breeding in white-breasted mesites (Mesitornis variegata)
No full textAlthough cooperative breeding is known from only about 9 % of bird species, it has received substantial attention because individuals foregoing their own reproduction to help others represent a long-standing evolutionary puzzle. We studied group formation, breeding system, spatial distribution and several life-history traits of white-breasted mesites (Mesitornis variegata). Based on field observations across 3 years, we found that white-breasted mesites live in year-round stable pairs, and that groups are formed by juvenile philopatry. As other family-living birds, M. variegata exhibit a slow pace-of-life, characterized by high annual adult survival, low productivity, long chick dependence and extended parental care. However, although reproduction is monogamous and juveniles showed interest in their parents’ nests, we found no evidence of cooperative breeding. We suggest that slow life-histories, extended parental care and year-round territoriality predispose juvenile mesites to delay dispersal. However, adult intolerance toward older juveniles may prevent them from adopting a cooperative lifestyle. Comparisons with other species of mesite indicate that monogamy and delayed juvenile dispersal are necessary, but not sufficient for the evolution of cooperative breeding in this family of birds, and that particular ecological and social conditions have facilitated the transition from pair-living to a type of group that may represent a stepping stone in the evolution of cooperative breeding in mesites and other birds
Characterization of 10 polymorphic microsatellite loci for White-breasted mesites (Mesitornis variegata)
Get PDFWe characterized 10 specific microsatellite loci for White-breasted mesites (Mesitornis variegata), an endemic bird species from western Madagascar. Nine loci were in Hardy–Weinberg equilibrium, and we detected 4–10 alleles per locus (mean = 6.1). These primers will be used to study the mating system and social organization of White-breasted mesites and may have applications for the conservation of the few remaining populations of this vulnerable and still poorly studied species
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
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
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