1,721,013 research outputs found
Long-distance movements in pelagic seabirds: at-sea behaviour and life-history consequences
Full text linkThroughout their lives, animals have to make trade-offs between current and future events in their annual cycle. Long-lived migratory species in particular have to balance the cost of reproduction with adult overwinter survival, which is heavily dependent on migration. Behavioural plasticity, perhaps through experience and learning, may play a role in shaping individual variations in life-history decisions. The mechanisms by which such variations develop, and their potential effects on life-history traits, are poorly understood. This thesis uses two species of long-lived migratory seabirds, the Atlantic puffin Fratercula arctica and the Manx shearwater Puffinus puffinus, to address these questions, combining spatial tracking data with fine-scale measures of individual behaviour during long-distance at-sea movements. At-sea behaviour (measured with estimates of daily activity budgets) varied amongst individuals of different sex, age, and colonies. Individual variations in non-breeding behaviour were affected by investment in the previous season, and such variations had important implications for individual fitness. Puffins which visited the Mediterranean Sea foraged more and had a higher breeding success than puffins which remained locally. In addition, females puffins which foraged more during the winter, regardless of their location, laid earlier (which is associated with higher fledging success) and had a higher breeding success. Shearwaters which invested more in reproduction and started fall migration later spent less time resting at the wintering grounds than in other years, laid later and had a lower breeding success the following season. Shearwaters which invested less in reproduction showed the opposite trend. These behavioural differences were reflected in the birds' energy expenditure. Higher energy expenditure often correlated with higher fitness. Finally, pairs of puffins which followed similar migratory routes laid earlier the following year, why this was the case remained unclear. Environmental conditions were likely drivers of individual variation in at-sea behaviour. Puffins from multiple colonies across their breeding range spent more time foraging when in colder and productive waters. Furthermore, puffins from colonies at higher latitudes foraged in colder waters, despite not necessarily remaining close to their colony; this suggests a local adaptation to temperature. In shearwaters, immature individuals foraged in less productive waters than breeding adults, which resulted in a lower foraging efficiency (mass gain per unit of time spent foraging). Spatial segregation occurred between individuals of different age, sex, colonies and potentially individuals of different quality, often accompanied by differences in activity budgets. Although intra-specific competition was a likely driver of the observed segregated at-sea distributions - for example between immature and breeding shearwaters - it was unlikely to be the only factor. Spatial segregation between pair members in puffins in the months leading to the breeding season, accompanied with higher female foraging effort and breeding success, suggests that segregation resulted from different energy or nutritional requirements, perhaps related to egg laying. Overall, this thesis highlights how the investigation of the behaviours underlying long-distance movements can be a powerful tool to study drivers of breeding and non-breeding distributions and migratory routes, and the important consequences that individual variation in behaviour may have on individual fitness, and ultimately on population dynamics and the evolution of life-histories
Understanding seabird behaviour through long term tracking data
Full text linkComprehending how organisms maximise their reproductive success in an ever-changing environment lies at the core of animal behaviour studies. However, animals that inhabit highly dynamic habitats often pose challenges for direct observation. Biologging deployments facilitate remote monitoring of animals in otherwise inaccessible environments, particularly pelagic species. In this thesis, I harnessed an extensive geolocator dataset spanning multiple colonies to extract novel behavioural insights concerning the Manx Shearwater (Puffinus puffinus), a procellariform seabird known for its extreme life history strategy. Their remarkable migration across hemispheres to synchronize with seasonal food availability presents a unique array of challenges. Firstly, I unveil the ability of individual shearwaters to plastically adjust their over-wintering distribution in response to the El Niño Southern Oscillation. However, decreased foraging activity during El Niño years initiates carry-over effects on subsequent breeding, resulting in a reduction of chick provisioning efforts. Additionally, I elucidate how shearwaters adjust their southbound migratory patterns based on breeding phenology. Birds that breed later and subsequently postpone their post-breeding migration take shorter duration migrations with fewer foraging stopovers. Notably, these late-departing birds optimize their flight with lunar cycles, strategically utilizing moonlit nights for visually guided flight. Next, I investigate how seasonal fluctuations in photoperiod influence light-limited chick provisioning behaviours. I find that extended daylight promotes increased foraging and provisioning efforts, albeit accompanied by shorter nights, diminishing adults' ability to mitigate predation risks through moonlight avoidance. Lastly, I delve into how sex-specific reproductive roles influence diving behaviour during pre-laying using dive logger deployments. I discern that males exhibit increased diving efforts during pre-laying, and are less able to exploit evening foraging opportunities due to heightened colony attendance for nest defence. I also employed a pioneering DNA metabarcoding analysis of Manx shearwater diet, identifying six distinct fish species consumed by breeding adults. This thesis exemplifies the application of advanced analytical techniques to long-term biotelemetry data, providing valuable insights into individual animal behaviour
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
The mechanisms and consequences of parental coordination in Procellariiform seabirds
Full text linkBiparental care is a longstanding evolutionary conundrum. Why should parents continue to
invest in their offspring cooperatively, when by abandoning their partner they can reap all the
benefits with none of the work? Since the 1970s, several models have attempted to explain the
evolution and maintenance of biparental care in animals, eventually converging on the solution of
conditional cooperation: a parent’s behaviour should depend on the investment decisions of its
partner. This responsive strategy can lead to apparent coordination between parents, and many
empirical examples have since been reported. However, it is difficult to determine whether there
is active behavioural coordination between parents, or indeed the mechanisms underlying it. This
thesis uses two long-lived, monogamous seabird species, the Manx shearwater Puffinus puffinus
and the black-browed albatross Thalassarche melanophris, to investigate the occurrence and
mechanisms of coordinated parental behaviour. Using both experimental field manipulations and
quantitative observations I investigated the evidence for parental coordination in these species, and
the mechanisms and information parents may use to achieve it. Firstly, I examined the incubation
behaviour of parent Manx shearwaters, and found that their investment decisions were underlain
largely by their available body mass reserves, matching life-history predictions that long-lived
species should be selected to prioritise their own condition. Specifically, foraging birds determined
how long they should spend at sea by the amount of mass gains they needed to make on their trip,
with lighter birds spending proportionally more time foraging. However, I found that this decision
was modulated by the partner’s condition, with birds curtailing their trips when their partner
was in poor condition, suggesting that cooperative processes, perhaps facilitated by a process
of negotiation, may drive the coordination of care during incubation in this species. For chickrearing
shearwaters, I examined whether direct communication, or indirect information garnered
from the behaviour of the chick, might facilitate the coordination of nest visitation. Neither
putative sources of information appeared necessary for coordination in this species, and it was
not possible to determine conclusively what information drives provisioning behaviour. Instead,
I introduced the possibility that coordination at this breeding stage emerges passively through
an entrainment process during incubation. Finally, I investigated the potential role of intra-pair
display in facilitating coordination in the black-browed albatross, with a focus on allopreening. I
report tentative evidence that display forms part of an assessment process whereby the outgoing
parent determines its partner’s willingness to invest in care, which may ultimately contribute to
decision-making processes relating to foraging trip duration. Overall, I present evidence that
biparental care in these species may be underlain by nuanced systems of intra-pair coordination,
giving further insight into why and how animals are able to achieve cooperative behaviour
Patterns of vagrancy and long-distance dispersal in migratory birds
Full text linkVagrancy, the process in which organisms travel far outside of their known species’ breeding and wintering range, has long been thought to be an aberrant trait. Vagrants are hypothesised to result from a series of individual mistakes, such as inheritance of an incorrect compass bearing, or displacement by wind or weather systems. Though previous studies on vagrancy do not provide sufficient evidence to support these hypotheses, vagrancy still remains understudied. This thesis uses a combination of experimental field techniques, and indirect methods, to study how and why vagrancy occurs in migratory birds. More specifically, I investigated whether vagrants differ behaviourally from non-vagrants, and what factors drive vagrant occurrence. Firstly, I tested the orientation behaviour of vagrant and non-vagrant passerines to determine whether vagrants are capable of selecting a preferred migratory bearing. That is, are vagrants capable of initiating directed migratory flights? I found that not only do vagrants select a preferred orientation, but that orientation did not significantly differ from that of our non-vagrant control species, the Blackpoll Warbler (Setophaga striata). Both vagrants and non-vagrants oriented on a north/northwesterly heading, which is consistent with studies on post-fledging exploration of Blackpoll Warblers. This suggests that vagrancy may be linked to post-fledging exploration. Feathers from these vagrants were also assessed for the ratio of stable-hydrogen isotope (deuterium; δ2H) to pinpoint their natal origin. The majority of vagrants were found to originate from the edge of their breeding range, which has been associated with increased exploratory behaviour in other species of passerines. External factors that may drive vagrant occurrence were also examined. For vagrant New World warblers, the size of the overall breeding population and vagrant distance were found to best predict vagrancy. Furthermore, when examined at the regional level, each species was best predicted by the annual variation in population size and growth at the edge of their breeding range, supporting my results that vagrants originate along the range edge. Additionally, this relationship was negative, suggesting quadratic density-dependence, whereby vagrants irrupt in years of plentiful resources as the population increases, and erupt in years of depleting resources, when the population exceeds available food or habitat. I tested whether this relationship could be used to infer the source population of vagrants indirectly, using vagrant Lesser Black-backed Gulls (Larus fuscus). Though it was possible to infer their origin, increased survey efforts are needed to improve predictions. Finally, since vagrants are irruptive, I investigated irruptions in the Northern Saw-whet Owl (Aegolius acadicus) to determine drivers of irruption cycles in this species. Irruptions were strongly influenced by prey abundance, which suggests that vagrants may respond to food availability. Overall, this thesis challenges the idea that vagrants are aberrant, and instead suggests that this behaviour is within the scope of the normal migratory programme
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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