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
When corals eat plastics
24.05.2018 | Justus-Liebig-Universität Gießen
Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences