Scientists from the Johannes Gutenberg University Mainz, the University of California at San Diego and Stanford University have used a novel approach to investigate which factors are decisive for clutch size, thus presenting the first global analysis of the clutch sizes of birds.
"We have found a clear north/south divide," reported Professor Dr Katrin Böhning-Gaese of the Institute for Zoology at Mainz University. "In northern latitudes, the birds lay more eggs, while in the tropics they lay fewer eggs." The decisive reason for the different clutch sizes, according to the scientists, is the difference in temperature between summer and winter and the associated consequences for the life of the birds. The results were recently published in the latest edition of the scientific journal PLos Biology.
Great tits lay seven to ten eggs in their nest, while the gray partridges lay ten to twenty - in some cases even up to 29. The nests of culvers, on the other hand, contain only two eggs at the same time, but they do lay several times a year. The griffon vulture, which used to breed in Germany, only lays one egg per nest each year. To explain these differences, two different approaches have been used thus far: either the clutch sizes were related to biological characteristics, such as body weight, or environmental factors such as climate were investigated. In the study now being presented, the scientists combined these two approaches, while also having access to the largest data set worldwide. "We have collected and analyzed records of almost 5,300 bird species and their different characteristics. This is by far the most extensive data collection there is," says Cagan Sekercioglu, one of the co-authors of the study. The bird expert does point out, however, that the data situation is not entirely standardized. The British, for example, have always been enthusiastic hobby ornithologists who carefully observed the bird population in their former colonies and wrote down their findings; this is why countries such as India have excellent documentation, while for Oceania data are only available for about sixteen percent of the species.
The evaluation of the enormous data set showed that it can be explained how many eggs a female bird would normally lay in her nest by looking at only a few factors. The greater the temperature difference between summer and winter, the more eggs the birds produce. This explains the larger number of eggs in Europe and North America and the smaller clutch size in the tropics. "As far as tropical birds are concerned, for example, warblers have only two young, but they feed and care for them for a period of more than two months," explains Böhning-Gaese. "This means having few offspring, but caring for them as well as possible." The researchers also found that nidicolous birds such as blackbirds and tits lay fewer eggs than nidifugous birds such as game birds. Cavity nesters such as tits and woodpeckers lay larger clutches of eggs than open-nesting species. "This is actually quite remarkable, as studies about the survival of bird populations would lead one to expect that cavity nesters are better protected against predators." The body size of the species in question, on the other hand, is far less important for the number of eggs than one would have expected.
The combination of two approaches - the so-called intrinsic factors based on the biology of the species and the macro-ecological factors - in one analysis marks a turning point in the research: what would once have been two individual disciplines are now recombined to form a new synthesis. This could be of advantage for the protection of the environment and of species. Walter Jetz, the primary author of the study, remarked: "Our results have shown that not only the habitat of a species but also its way of life are closely related to the climate. Rapid climate changes can therefore destroy links between behavior and climate that have developed over a long period, thus posing an additional risk factor for a species."
Böhning-Gaese concludes: "We can use such analyses for a correct prediction of the average clutch size of a bird species anywhere on earth with a high probability. This may also help to protect certain species from extinction. Species that lay few eggs are more at risk from human intervention, environmental catastrophes, and global climate change." An example are albatrosses, many species of which lay only one egg every two years and which are at risk of extinction as a result of long-line fishing in the Antarctic Ocean.
Prof Dr Katrin Böhning-Gaese | alfa
Litter is present throughout the world’s oceans: 1,220 species affected
27.03.2017 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
29.03.2017 | Materials Sciences
29.03.2017 | Physics and Astronomy
29.03.2017 | Earth Sciences