104,793 research outputs found
Studies on breeding shorebirds at Medusa Bay, Taimyr, in summer 2001
No full textIn the Summer of 2001 a combined Dutch-Russian expedition took place to the Willem Barentz field station at Medusa Bay near Dikson in north-western Taimyr. The expedition was organized by Alterra, the Working Group for International Waterbird and Wetland Research (WIWO) and the Agricultural Department of the Dutch Embassy in Moscow. The results obtained by the Alterra team are presented in this report. Subjects of study generally concerned breeding biology of arctic breeding shorebirds, especially aspects related to timing of breeding and adult body condition. This report's purpose is not to discuss the findings thoroughly but merely to summarize the research questions addressed and present all basic information collected during the 2001 season. Topics included are spring arrival and autumn departure of waders from the tundra, breeding phenology, nest success, biometrics of adult waders, chick growth rate, return rates of adult shorebirds, and seasonal and weather-related variation in arthropod availability. Where useful, results are compared with data collected in a previous expedition in 2000. More elaborate analyses and discussion of the data will be made elsewhere
Mortality of Black-tailed Godwit Limosa limosa and Northern Lapwing Vanellus vanellus chicks in wet grasslands: influence of predation and agriculture
No full textGrassland-breeding shorebirds show widespread declines due to a reduction in breeding productivity following agricultural intensification. However, there is also concern that increasing predation causes further declines or precludes population recovery. Predation may itself be enhanced by agriculture through changes in habitat or food availability, but little is known about the mortality of nidifugous shorebird chicks. We studied mortality by radio-tagging 662 chicks of Black-tailed Godwit Limosa limosa and Northern Lapwing Vanellus vanellus in 15 farmland sites in the Netherlands. Tagging and handling had no effect on the condition and survival of godwit chicks, but body condition was reduced by 6-11% in lapwing chicks wearing a tag for longer than 3 days. Fledging success was 0 - 24% in both species. Mortality was highest in young chicks but remained considerable until after fledging. Losses were traced mostly to predators (70 - 85%; 15 species, predominantly birds), but a! t least 5 - 10% were due to mowing, and 10 - 20% were due to other causes, including entrapment in ditches and starvation. Chicks staying in fields that were cut before the next radio check were found much more often as mowing victims and somewhat more often as prey remains than chicks in fields not cut, indicating that predation includes a limited amount of scavenging. The predation hazard for godwit chicks was higher in recently cut or grazed fields than in the tall, uncut grasslands they preferred, while that for lapwing chicks was lowest in grazed fields. In godwit chicks, poor body condition increased mortality risk, not only from starvation but also from other causes. Predation on godwit chicks was thus enhanced by intensive farming through a decline in the availability of cover, augmented by a reduced body condition, possibly due to food availability problems. Changes in farming practice may therefore help reduce predation pressure, though the observed interactions e! xplained only part of the high predation rate in godwits and n! one in l apwings. Predator abundance has increased in Dutch wet grassland regions, and chick predation has become a factor that should be considered in planning the type and location of conservation measures.
Mechanisms promoting higher growth rate in arctic than in temperate shorebirds
No full textWe compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate. Growth rate of knot chicks was very high compared to other, mainly temperate, shorebirds of their size, but strongly correlated with weather-induced and seasonal variation in availability of invertebrate prey. Red knot chicks sought less parental brooding and foraged more at the same mass and temperature than chicks of three temperate shorebird species studied in The Netherlands. Fast growth and high muscular activity in the cold tundra environment led to high energy expenditure, as measured using doubly labelled water: total metabolised energy over the 18-day prefledging period was 89% above an allometric prediction, and among the highest values reported for birds. A comparative simulation model based on our observations and data for temperate shorebird chicks showed that several factors combine to enable red knots to meet these high energy requirements: (1) the greater cold-hardiness of red knot chicks increases time available for foraging; (2) their fast growth further shortens the period in which chicks depend on brooding; and (3) the 24-h daylight increases potential foraging time, though knots apparently did not make full use of this. These mechanisms buffer the loss of foraging time due to increased need for brooding at arctic temperatures, but not enough to satisfy the high energy requirements without invoking (4) a higher foraging intake rate as an explanation. Since surface-active arthropods were not more abundant in our arctic study site than in a temperate grassland, this may be due to easier detection or capture of prey in the tundra. The model also suggested that the cold-hardiness of red knot chicks is critical in allowing them sufficient feeding time during the first week of life. Chicks hatched just after the peak of prey abundance in mid-July, but their food requirements were maximal at older ages, when arthropods were already declining. Snow cover early in the season prevented a better temporal match between chick energy requirements and food availability, and this may enforce selection for rapid growth.
Effect van nestbezoek en onderzoek op weidevogels
No full textIn Nederland wordt veel energie gestoken in het zoeken en beschermen van weidevogellegsels tegen agrarische activiteiten om zo de gestage achteruitgang van weidevogels te stoppen. Jaarlijks betreft dit zo’n 150.000 nesten. Er is echter discussie ontstaan over het positieve effect van dit soort beschermingsmaatregelen omdat het controleren van nesten tot een verhoging van de verliezen zou kunnen leiden; het zogenaamde bezoekeffect. Om dit vast te kunnen stellen is allereerst gezocht naar een berekeningswijze waarmee een eventueel bezoekeffect kan worden aangetoond. Hiervoor zijn in totaal drie verschillende modellen ontwikkeld en getest. De verschillende modellen zijn uitgetest met een gesimuleerde dataset waarin de waarden voor de dagelijkse overlevingskans en het bezoekeffect bekend zijn. De beste schattingen van het bezoekeffect en de dagelijkse overlevingskans worden behaald met een model waarin tevens de broedduur en de eerste eilegdatum zijn gemodelleerd
Breeding success of Black-tailed Godwits Limosa limosa under 'mosaic management' : an experimental agrienvironment scheme in The Netherlands
No full textBlack-tailed Godwits (Limosa limosa) have been declining for decades in The Netherlands and so far this has not been slowed by conservation measures. A new form of agri-environment scheme was tried out in 2003-2005 at 6 sites where a ‘grassland mosaic’ (200-300 ha) was created by collectives of farmers through a diverse use of fields including postponed and staggered mowing, (early) grazing, creating ‘refuge strips’ during mowing, and active nest protection. We measured breeding success of godwits in each of the experimental sites and nearby, paired controls. Breeding success was higher (0.28 chicks fledged / pair) in mosaics than in controls, but due to lower agricultural nest losses only. Chick survival was 11 % in both mosaics and controls. The amount of late-mown and other grassland suitable for chicks hardly differed between treatments during the fledging period, mainly due to rainfall delaying postponed mowing in all sites. Chick survival was however positively correlated with site variation in the amount of high grass (>18 cm). Breeding success was high enough to compensate for adult mortality (ca. 0.6) in only one mosaic site. Chick survival was lower than in previous Godwit studies, indicating that additional loss factors have increased. Predation (50-80 % of chicks, mostly by birds) is a candidate, but changes in the suitability of late-mown grassland (insect abundance and sward density in grass monocultures) may also play a role. Consequently a higher management investment is needed to achieve a self-sustaining population.Die niederländische Brutpopulation der Uferschnepfe (Limosa limosa) verzeichnet über die letzten Jahrzehnte hinweg eine kontinuierliche Abnahme. Diese Bestandsabnahme konnte bislang auch durch Schutzmaßnahmen nicht aufgehalten werden. Deshalb wurde in den Jahren 2003 – 2005 in sechs Grünlandgebieten mit je 200 – 300 ha Fläche eine neue Form des Vertragsnaturschutzes getestet. Dabei haben die in einem Verbund zusammengeschlossenen Landwirte ein vielfältiges Bewirtschaftungsmosaik praktiziert, das unter anderem variable, gestaffelte Mahdtermine (mit Möglichkeit der Verlegung auf einen späteren Termin), eine (frühe) Beweidung, die Anlage von Fluchtstreifen während der Mahd und aktiven Gelegeschutz vorsah. Um die Wirksamkeit des Programms zu überprüfen, wurde der Bruterfolg der Uferschnepfe in den Vertragsgebieten mit angrenzenden Kontrollgebieten vergleichend untersucht. Die Mosaikbewirtschaftung führte in den Testgebieten zu einem höheren Bruterfolg (0.28 vs. 0.16 Küken pro Paar) gegenüber den Kontrollgebieten, allerdings nur infolge der geringeren Gelegeverluste durch die Landwirtschaft. Die Kükenüberlebensrate lag in beiden Gebieten bei 11 %. Entgegen den Erwartungen unterschied sich die Zahl der Aufzuchthabitate (hier: u.a. spät gemähte Wiesen mit hochwüchsiger Vegetation) zwischen den Test- und Kontrollgebieten während der Schlupf- und Aufzuchtphase kaum. Dieses Ergebnis geht weder auf die Landwirte selbst noch auf
die beschriebenen Managementbestimmungen zurück, sondern ist vielmehr das Resultat von Niederschlagsereignissen, die auf allen Flächen zu einer verspäteten Mahd führten. Unter Berücksichtigung der Gebietsunterschiede korrelierte
die Überlebensrate der Küken positiv mit dem Flächenanteil höherer Gräser (>18 cm). Der für den Bestandserhalt notwendige Bruterfolg zur Kompensation der Adultsterblichkeit (ca. 0.6 Küken/Paar) wurde in nur einem Testgebiet mit Mosaikbewirtschaftung. Im Vergleich mit früheren Studien lag die Kükenüberlebensrate sogar niedriger. Dies legt den Schluss nahe, dass weitere, zusätzliche Verlustursachen an Bedeutung gewonnen haben. In Frage kommen hier ein zunehmendes Prädationsrisiko (50-80 % aller Küken; meistens durch Vögel verursacht) aber auch Veränderungen in der Verfügbarkeit und Eignung spät gemähter Grünländflächen. In Bezug auf die Eignung von Grünlandflächen als Aufzuchthabitate dürften insbesondere der Arthropodendichte und der Dichte der Vegetation Bedeutung zukommen. Die bisherigen Ergebnisse machen deutlich, dass der Umfang der Artenschutzmaßnahmen deutlich gesteigert werden muss, um eine tragfähige Uferschnepfenpopulation langfristig zu erhalten
Body condition of shorebirds upon arrival at their Siberian breeding grounds
No full textArctic breeding shorebirds carry substantial body stores on their long-distance migrations from their non-breeding grounds. Upon arrival at the breeding area the remains of these stores can be used for egg formation, insurance against poor feeding conditions or rebuilding organs. We quantified body condition (body mass, total body water, lean body mass and fat mass estimated using the deuterium dilution method) in seven shorebird species caught upon arrival in the Siberian Arctic. Arrival condition was compared with incubation condition in a subset of species. After correction for structural size, body mass was significantly lower at arrival than during incubation in most of the species (but 3–18% above lean mass). Fat index (fat mass/lean mass) varied between 5.1 and 13.2%. Fat stores were estimated to enable survival for 0.6 days for the smallest and 2.5 days for the largest species. We discuss possible functions of arrival stores: insurance, egg-formation or rebuilding organs.
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
Eggs in the freezer: energetic consequences of nest site and nest design in Arctic breeding shorebirds
No full textBirds construct nests for several reasons. For species that breed in the Arctic, the insulative properties of nests are very important. Incubation is costly there and due to an increasing surface to volume ratio, more so in smaller species. Small species are therefore more likely to place their nests in thermally favourable microhabitats and/or to invest more in nest insulation than large species. To test this hypothesis, we examined characteristics of nests of six Arctic breeding shorebird species. All species chose thermally favourable nesting sites in a higher proportion than expected on the basis of habitat availability. Site choice did not differ between species. Depth to frozen ground, measured near the nests, decreased in the course of the season at similar non-species-specific speeds, but this depth increased with species size. Nest cup depth and nest scrape depth (nest cup without the lining) were unrelated to body mass (we applied an exponent of 0.73, to account for metabolic activity of the differently sized species). Cup depth divided by diameter 2 was used as a measure of nest cup shape. Small species had narrow and deep nests, while large species had wide shallow nests. The thickness of nest lining varied between 0.1 cm and 7.6 cm, and decreased significantly with body mass. We reconstruct the combined effect of different nest properties on the egg cooling coefficient using previously published quantitative relationships. The predicted effect of nest cup depth and lining depth on heat loss to the frozen ground did not correlate with body mass, but the sheltering effect of nest cup diameter against wind and the effects of lining material on the cooling coefficient increased with body mass. Our results suggest that small arctic shorebirds invest more in the insulation of their nests than large species
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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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