In Wieringermeer, a typical Dutch polder that was reclaimed from the sea in 1930, Bewick’s swans stop by during migration to feed on the leftovers of sugarbeets that remain after the farmer’s harvest. The ornithologists were interested in why some fields were used more intensively than others, while all fields seem to offer similar amounts of food right from the start.
They wondered: "In case foraging benefits seem to be equal across all fields, there may be variation in foraging costs that may explain the observed spatial heterogeneity in exploitation." The authors showed, in the May issue of the American Naturalist, that the time spent feeding on a field by a flock of swans can be used as a surrogate of an individual’s energy intake rate (which declines over time due to depletion). This showed that an individual’s intake rate at abandoning a field, which should reflect the foraging cost as experienced by the bird itself, decreased with the distance to roads and increased with the distance to its nighttime roost.
The higher intake rates at which fields near roads were given up reflected the chance to be disturbed by humans. The higher intake rates at which fields far from roosts were given up could be explained by the energetic cost of flight, which are substantial for large birds such as Bewick’s swans. When taking these flight costs into account, the authors calculated that the net benefits at which each field was given up corresponded with the net benefits obtained in the long run. The latter was measured via regular visual inspection of the thickness of each bird’s belly!
All these insights into foraging costs could be implemented into a model that predicted the number of swans that potentially could stop by at the site. This model accurately and correctly predicted the true number of birds that made use of the stopover. It could thus serve as a valuable tool to manage and protect the relatively small population of Bewick’s swans wintering in NW Europe, which declined from 30,000 to 20,000 birds over the last 15 years.
Patricia Morse | EurekAlert!
Bioinvasion on the rise
15.02.2017 | Universität Konstanz
Litter Levels in the Depths of the Arctic are On the Rise
10.02.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport
Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...
The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.
The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...
Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...
Nanometer-scale magnetic perforated grids could create new possibilities for computing. Together with international colleagues, scientists from the Helmholtz Zentrum Dresden-Rossendorf (HZDR) have shown how a cobalt grid can be reliably programmed at room temperature. In addition they discovered that for every hole ("antidot") three magnetic states can be configured. The results have been published in the journal "Scientific Reports".
Physicist Dr. Rantej Bali from the HZDR, together with scientists from Singapore and Australia, designed a special grid structure in a thin layer of cobalt in...
13.02.2017 | Event News
10.02.2017 | Event News
09.02.2017 | Event News
24.02.2017 | Life Sciences
24.02.2017 | Life Sciences
24.02.2017 | Trade Fair News