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Barn swallows long-distance migration occurs between significantly temperature-correlated areas
Get PDFOrganisms are routinely confronted with crucial decisions on the best time and place to perform fundamental activities. However, unpredictable spatio-temporal variation in ecological factors makes life-history optimization difficult particularly for long-distance migrants, which are putatively blind of conditions thousands of kilometers and weeks ahead along their journey. Here we challenge, on a hierarchy of geographical scales, the common wisdom that migratory birds have no clue to ecological conditions at destination. Using ringing data of the inter-continental migrating barn swallow (Hirundo rustica), we show that temperatures at breeding sites and at times of arrival from migration are more correlated with those at actual wintering sites and at times of departure than with those at other sites and at periods before/after departure. Hence, individual swallows have clues to adjust timing of spring migration based on expected conditions at destination, and they apparently choose wintering sites to increase availability of such information
Data analysis and models for long-distance bird migration. From correlations on ring recoveries to machine learning on geolocator measurements
Get PDFIl clima è uno degli elementi plasmanti degli ecosistemi. I suoi continui cambiamenti influenzano profondamente il comportamento, la distribuzione e la dinamica delle popolazioni animali e vegetali. Gli uccelli migratori sono tra le specie più interessate da questo fenomeno, in quanto regolano la loro fenologia in base alle condizioni climatiche delle loro aree di riproduzione e di svernamento. Per indagare su come e in che misura le alterazioni dei regimi climatici possono determinare I cambiamenti cruciali nell'ecologia del movimento degli uccelli migratori, sono necessarie una conoscenza dettagliata dei loro siti di stazionamento e una ricostruzione affidabile delle loro rotte migratorie e del timing dei loro viaggi. I metodi classici per studiare la migrazione, come l’inanellamento degli uccelli, ora possono essere integrati da nuove tecnologie, come i GPS loggers o i light-level geolocator, che consentono di registrare dei proxy delle posizioni degli organismi durante le loro rotte.
Concentrandoci su una sola specie, la rondine (Hirundo rustica), in questo lavoro abbiamo per prima cosa sviluppato un metodo per studiare la presenza di connessioni climatiche tra le aree di svernamento africane e le aree di riproduzione europee di questo uccello migratore passeriforme: sono emerse correlazioni sorprendentemente significative tra le temperature medie dei siti di svernamento e le posizioni di riproduzione degli individui nelle settimane interessate dalla migrazione primaverile. Le correlazioni hanno un’elevata significatività solo in prossimità dei siti di svernamento e solo se le serie di temperature si riferiscono all’esatto periodo di migrazione. In secondo luogo, abbiamo ricostruito le rotte migratorie di 88 rondini usando le misurazioni fornite da light-level geolocator, verificando la ripetibilità del metodo di stima utilizzato. I risultati ottenuti ci hanno permesso di identificare quattro gruppi di individui e un possibile effetto dell'anno di migrazione su molti indicatori delle rotte ricostruite. Infine, utilizzando i dati analizzati durante la seconda parte della ricerca, abbiamo automatizzato una lunga fase manuale di pre-elaborazione dei dati dei geolocator implementando filtri basati su algoritmi di Machine Learning. Le rotte migratorie ricostruite utilizzando la pre-elaborazione automatica sono completamente confrontabili con quelle ottenuto dalla selezione manuale dei dati. Questo lavoro conferma che modelli basati su dati raccolti con dispositivi ICT potrebbero essere utili strumenti per approfondire l'influenza dei cambiamenti ambientali e climatici sulla connettività delle specie e degli ecosistemi.Climate is one of the fundamental shapers of ecosystems, thus its ongoing changes deeply influence the behavior, distribution and dynamics of plant and animal populations. Migratory birds are among the species most affected by this phenomenon, as they need to fine-tune their phenology according to the climatic conditions of their breeding and wintering areas. To investigate how and to what extent alterations of climate regimes may determine key changes in the movement ecology of migratory birds, a detailed knowledge of their staging sites, a trustable reconstruction of their migration routes and of the time schedules of their journeys is very necessary. The classic methods for studying migration, such as bird ringing, can now be complemented by new technologies, such as GPS loggers or light level geolocators, that allow to record proxies of organisms’ positions throughout their routes.
Focusing on a model species, the barn swallow (Hirundo rustica), in this work we first developed a method to investigate the occurrence of climatic connections between the African wintering and European breeding areas of this migratory passerine bird: surprisingly significant correlations between the average temperatures in the wintering and breeding locations of individuals emerged at the precise weeks of individuals’ spring migration. Correlations have high significance only in the proximity of barn swallow wintering sites and if the temperature series refer to the precise weeks of migration. Second, we reconstructed migratory routes of 88 barn swallows using the measurements provided by light level geolocators, verifying the repeatability of the estimation method we used. The results obtained allowed us to identify four groups of individuals, as well as a possible effect of the year of migration on many indicators of the migration schedules obtained from the reconstructed routes. Third, using the routes data as reconstructed in the second research step, we have automated a long manual phase of data pre-processing by implementing filters based on Machine Learning algorithms. The migratory routes reconstructed using the automated pre-processing are completely comparable with those obtained from the manual selection of geolocator data. The work confirms that models based on data gathered with ICT devices may be helpful tools to let us gain insights on the influence of environmental and climate changes on species and ecosystems connectivity.DIPARTIMENTO DI ELETTRONICA, INFORMAZIONE E BIOINGEGNERIASystems and Control31CASTELLETTI, ANDREA FRANCESCOPERNICI, BARBAR
Analisi di correlazione climatica tra aree interessate da connettività migratoria
No full textLAUREA MAGISTRALEIl clima è una delle componenti abiotiche fondamentali degli ecosistemi. I rapidi cambiamenti che osserviamo da mezzo secolo influiscono profondamente sul comportamento, la distribuzione e la dinamica di popolazioni di piante e animali.
Gli uccelli migratori sono tra le specie che più risentono di questo fenomeno, in quanto gran parte della loro fenologia è fondata sulle condizioni climatiche delle loro aree di riproduzione e svernamento. La comprensione di quali meccanismi determinino il comportamento della migrazione sono fondamentali per la previsione degli impatti a cui essa andrà incontro nei prossimi decenni.
Per questo tipo di analisi è necessaria una più approfondita conoscenza delle regioni interessate dalla migrazione e del periodo temporale in cui essa avviene. Il classico metodo di marcatura e ricattura è oggi supportato da nuove tecnologie e studi, come la telemetria da satellite e l’analisi degli isotopi stabili.
In questo mio lavoro di tesi ho analizzato le possibili correlazioni presenti a scala sub-continentale (in Europa e in Africa) tra le variabili di temperatura e precipitazione delle aree connesse dalla migrazione della rondine (Hirundo rustica), nel periodo caratterizzato dalla migrazione invernale.
I risultati mostrano la presenza di una significativa correlazione per i mesi di gennaio e febbraio tra la temperatura media e la precipitazione mensile dell’Africa subsahariana occidentale con la temperatura media mensile in Europa. La correlazione che presenta l’andamento più coerente con la connettività migratoria delle diverse aree è quella tra la temperatura media mensile dell’Africa subsahariana occidentale ed equatoriale e la precipitazione mensile dell’Europa, nel periodo gennaio-febbraio.
Queste evidenze, con un’analisi approfondita del loro trend temporale, possono portare allo studio e alla realizzazione di modelli clima-movimento, in grado di prevedere la dinamica spaziale e temporale dei fenomeni di migrazione.
Ho inoltre studiato il possibile legame tra l’inizio del periodo caratterizzato dalla presenza di precipitazioni più intense nell’Africa sub-sahariana (grazie alle quali le rondini possono accedere alle fonti di cibo necessarie ad affrontare la migrazione) e le condizioni climatiche tardo-invernali e primaverili in Europa. I coefficienti mostrano la presenza di una significativa correlazione negativa con la precipitazione del mese di febbraio nelle Isole Britanniche e nella zona del nord della Germania e della Danimarca, oltre a una lieve correlazione negativa con la temperatura media mensile di tutte le aree europee.
Tale risultato può servire come base per ulteriori stud
Across the deserts and sea: inter-individual variation in migration routes of south-central European barn swallows (Hirundo rustica)
Get PDFBackground The spatiotemporal organization of migratory routes of long-distance migrants results from trade-offs between minimizing the journey length and en route risk of migration-related mortality, which may be reduced by avoiding crossing inhospitable ecological barriers. Despite flourishing avian migration research in recent decades, little is still known about inter-individual variability in migratory routes, as well as the carry-over effects of spatial and temporal features of migration on subsequent migration stages. Methods We reconstructed post- and pre-breeding migration routes, barrier crossing behaviour and non-breeding movements of the largest sample (N = 85) analysed to date of individual barn swallows breeding in south-central Europe, which were tracked using light-level geolocators. Results Most birds spent their non-breeding period in the Congo basin in a single stationary area, but a small fraction of itinerant individuals reaching South Africa was also observed. Birds generally followed a 'clockwise loop migration pattern', moving through the central Mediterranean and the Sahara Desert during post-breeding (north to south) migration yet switching to a more western route, along the Atlantic coast of Africa, Iberia and western Mediterranean during the pre-breeding (south to north) migration. Southward migration was straighter and less variable, while northward migration was significantly faster despite the broader detour along the Atlantic coast and Iberia. These patterns showed limited sex-related variability. The timing of different circannual events was tightly linked with previous migration stages, considerably affecting migration route and speed of subsequent movements. Indeed, individuals departing late from Africa performed straighter and faster pre-breeding migrations, partly compensating for the initial departure delays, but likely at the cost of performing riskier movements across ecological barriers. Conclusions Different spatiotemporal migration strategies during post- and pre-breeding migration suggest that conditions en route may differ seasonally and allow for more efficient travelling along different migration corridors in either season. While highlighting patterns of inter-individual variability, our results support increasing evidence for widespread loop migration patterns among Afro-Palearctic avian migrants. Also, they suggest that carry-over effects acting across different phases of the annual cycle of migratory species can have major impacts on evolutionary processes
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
Reconstruction of long-distance bird migration routes using advanced machine learning techniques on geolocator data
Get PDFGeolocators are a well-established technology to reconstruct migration routes of animals that are too small to carry satellite tags (e.g. passerine birds). These devices record environmental light-level data that enable the reconstruction of daily positions from the time of twilight. However, all current methods for analysing geolocator data require manual pre-processing of raw records to eliminate twilight events showing unnatural variation in light levels, a step that is time-consuming and must be accomplished by a trained expert. Here, we propose and implement advanced machine learning techniques to automate this procedure and we apply them to 108 migration tracks of barn swallows (Hirundo rustica). We show that routes reconstructed from the automated pre-processing are comparable to those obtained from manual selection accomplished by a human expert. This raises the possibility of fully automating light-level geolocator data analysis and possibly analysing the large amount of data already collected on several species
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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