24. 05. 2022
Bird species whose males perform aerial displaying inhabit open rather than closed (forest) environments and are more likely to have multiple mates. They usually have more elongated wings, which is related to the fact that they migrate longer distances, and breed at higher latitudes, i.e. further from the equator. In addition, the aerial displaying seems to be relatively common in generally small passerine species with brightly coloured plumage. All of this suggests that the evolution of aerial displays in passerines is the result of both sexual and natural selection, as scientists from the Institute of Vertebrate Biology of the Czech Academy of Sciences and the Faculty of Science of Charles University have found in a recent comprehensive analysis. The results of the research have been published in the prestigious Proceedings of the Royal Society B journal.
“Our results suggest that aerial displays occur primarily in species with enhanced flight efficiency and flight capability, which would not be so surprising. However, we also found out that these bird species exhibit a stronger intensity of sexual selection,” says Tomáš Albrecht, the head of the Evolutionary Ecology of Birds research group at the Institute of Vertebrate Biology of the CAS. “This means that between the males, there are big differences in success among the females. A typical representative of a passerine that performs this way might be the European stonechat, skylarks, or some warbler species, such as Whitethroats.”
Obstacles to the research and the world’s largest passerine dataset
Data collection for this project was based on reading and compiling information from a large number of books and other literature. “To get the books, in particular, we had to visit libraries frequently, but they were closed due to the COVID-19 pandemic. So, we had to wait several weeks or months for the selected publications or to borrow one or two, go through them at home as quickly as possible, return them to the library and repeat the process several times,” explains Peter Mikula from the Institute of Vertebrate Biology of the CAS, the main author of the study.
“In total, we managed to collect information on 1,700 species of passerines, which is the largest dataset currently available on this interesting phenomenon in the world.”
“Thanks are due to all those who were willing to make the often rare and hard-to-get literature available.”
Thanks to the unique data and comprehensive analysis, the researchers were able to uncover the features that were most often repeated in the displaying fliers: more elongated wings, more partners, and, to a lesser extent, more colourful plumage and smaller body size. In addition to their visual characteristics, these fliers are also characterized by their habitat requirements and greater mobility: they tend to inhabit more open environments, migrate further and nest at higher latitudes (further from the equator).
Birdsong and display have never been properly studied
The initial impetus that led to the study of aerial displays of passerines in relation to the environment, was the repeated visits of Tomáš Albrecht to southern Africa. The terrestrial biomes there change rapidly, with semi-deserts replacing savannahs, which in turn are replaced by gallery forests and vice versa. “I have noticed that in each environment, the singing and aerial displays of the passerine communities have changed. It turned out that at the global level, this phenomenon has not been well described. This is because previous studies have only worked with a small number of species, on the scale of a few dozens, or focused on a single zoogeographic region. No one before us has been able to make a comprehensive synthesis using such a large dataset,” says Tomáš Albrecht, describing the beginnings of the research.
Why do birds behave like this?
“The behavioural ornaments of animals are yet a relatively neglected topic. Most studies dealing with the vertebrate sexual signals focus on the visual cues, such as the plumage coloration in birds and horns and antlers in ungulates, or the acoustic ones, such as the bugling of deer and the singing of birds,” says Peter Mikula. Researchers would therefore like to focus even more in the future on the sex-related behaviour of birds, about whose sexual life many interesting details have been collected in the recent decades with the help of hundreds or thousands of amateur ornithologists.
“Now, when precise data on the distribution of each species and on the phylogeny of this highly successful group of birds are also available, it is possible to proceed to global analyses on a scale that was unimaginable just a few years ago. In future studies, we would like to focus primarily on describing the relationships in sexual signalling, using the three main types of ornamentation in passerines: visual (feather colour), acoustic (song) and behavioural, which specifically includes aerial displaying, to understand how the environment influences the type of quality signalling across species in the context of sexual selection,” the authors of the study add.
Peter Mikula (firstname.lastname@example.org)
Tomáš Albrecht (email@example.com)