Skip to main content Skip to navigation

Successful avian flirtation: less is more

Successful courtship is a question of practice, and the most successful aren’t necessarily the biggest show-offs – alternative flirting strategies are just as promising. Subtle, demure behaviour, such as coyness, arouses curiosity and can increase the interest in a potential sexual partner. This sounds very human, but a recent study conducted by the Konrad Lorenz Institute for Ethology at the University of Veterinary Medicine Vienna analysed this behaviour in avian courtship. The review was published in the British scientific journal Proceedings of the Royal Society B.

The three researchers analysed previously published studies on avian courtship and suggest that sexual selection research has been dominated by the notion that the strongest, most impressive and most extravagant courtship displays will lead to the highest success in mate selection – in other words, that the displays best reflect the quality of the courter.

Subtle trumps vigorous

However, as the researchers note, courtship displays are often structured temporally and contain different elements with varying degrees of intensity and conspicuousness. “For example, highly intense movements are often coupled with more subtle components such as static postures or hiding displays,” as Thomas MacGillavry explains. The researchers refer to such subtle display traits as “coy”, as they involve the withholding of information about maximal display capabilities.

Three hypotheses for the success of coy courtship behaviour

The researchers examined the role of intensity variation within temporally dynamic displays and discuss three hypotheses for the evolution of coy courtship behaviours. Giovanni Spezie explains: “We first review the threat reduction hypothesis, which points to sexual coercion and sexual autonomy as important facets of sexual selection. We then suggest that variation in display magnitude exploits pre-existing perceptual biases for temporal contrast.” As a third hypothesis, the researchers propose that withholding information may leverage the receivers’ predisposition for filling in the missing gaps – a phenomenon they call “curiosity bias” – with the goal of arousing curiosity in potential sexual partners.

New insights for a better understanding of courtship behaviour

“Much like human music or theatre, courtship displays may constitute true performances in their own right, where different elements interact to entice, build suspense, surprise and excite the intended audience. The way in which such performances unfold over time represents a promising and novel direction for studies of courtship behaviour,” says Leonida Fusani. The underrepresentation of such aspects is due to the fact that behavioural research tends to break down behaviour into its components and does not look at it as a whole, the researchers say. Such an analysis, however, may not correspond to the actual interactions that occur during these kinds of courtship displays.

The article “When less is more: coy display behaviours and the temporal dynamics of animal courtship” by Thomas MacGillavry, Giovanni Spezie and Leonida Fusani was published in Proceedings of the Royal Society B.

Scientific article

Photos: Dominic Chaplin

Social experience enhances female attraction to male courtship songs

Male house mice produce complex ultrasonic vocalisations (USVs), especially during courtship and mating. Their calls are similar to birdsong, although they are inaudible to us because they are above the frequency range of human hearing (>20 kHz). Male courtship songs are attractive to females, but it depends on their social experience, as shown in a recent study conducted by Vetmeduni’s Konrad Lorenz Institute of Ethology.

In their study, the researchers conducted a playback experiment with wild female house mice (Mus musculus musculus) in which each subject was simultaneously presented with entering an area with recordings of male USVs versus another area playing a control recording with no male USVs. allowed to choose between an area with a speaker playing

The experiment aimed to test whether the females’ attraction to male USVs was influenced by any of the three factors, social experience (comparing females housed individually or socially with another female), sexual receptivity (comparing females were in oestrus or not), or neonatal paternal exposure (comparing females that were reared with or without their father). Previous studies suggested that these factors influence the attraction of female mice to male USVs, but the results were contrary to expectations and limited to inbred strains of laboratory mice.

Social experience has a positive effect, paternal exposure does not play a role

Overall, the females showed no attraction to the males' USVs, but it turned out to depend upon their housing. "We found that the females were attracted to male USVs if they were housed with another female, whereas females that were housed individually, showed the opposite response and avoided the male USVs,” says Sarah Zala from the Konrad Lorenz Institute for Ethology. "It is unclear why individual housing reversed females' attraction towards male courtship songs", she explains, "but living alone might make them more cautious about approaching an unfamiliar male."

“We also found that females showed more attraction towards male USVs when they were not in oestrus, and especially if they were not in oestrus and socially housed,” says co-author, Dustin Penn also from the Konrad Lorenz Institute for Ethology. "This oestrous effect is consistent with a previous study on laboratory mice, he points out, "but we have no explanation." Finally, early exposure to a father had no effect on the females’ preference for male USVs.

Social experience and sexual cycle make all the difference

In summary, this recent study shows that the attraction of wild female mice towards male courtship songs depended upon their social experience (housing) and oestrous stage. These results should facilitate research on the genetic control of hearing loss, often conducted with laboratory mice. The researchers emphasize how their findings show how seemingly unimportant factors, such as social housing and sexual cycle, can influence the behaviour of mice, despite that these and many other such variables are not usually reported in scientific papers. These results thus raise concerns that unreported variables potentially contribute to the "replication crisis" in science.

The article “Attraction of female house mice to male ultrasonic courtship vocalizations depends on their social experience and estrous stage” by Jakob Beck, Bettina Wernisch, Teresa Klaus, Dustin J. Penn and Sarah M. Zala was published in PLOS ONE.

Scientific article


Plastic instead of straw: Storks use human waste to build nests

Human-induced environmental pollution has a significant impact and even influences the nestbuilding of birds. This is shown by a recent European study led by the Konrad Lorenz Institute of Ethology at Vetmeduni using storks. However, the use of human waste differs significantly between individual stork populations.

Two major consequences of the ever-increasing human expansion are the conversion of natural habitats into agricultural land and the expansion of built-up areas. Related to this, human waste is also found just about everywhere. This has serious implications: Plastic pollution, in particular, is impacting wildlife worldwide. Discarded plastic is ubiquitous and increasingly a material for birds to incorporate into their nest structure - as now shown by a European research team from Spain, Poland and Austria using the white stork (Ciconia ciconia) as an example. In their study, the scientists describe the type, frequency and amount of anthropogenic nesting materials in two populations of the white stork in two geographically distant breeding areas, namely in Poland and in Spain.

Poland is not Spain: Significant differences in the use of plastic

In the total of 303 nests of the two populations, the researchers found significant differences in the use of anthropogenic nesting materials. To explain the reason of this, the scientist:in used remote sensing data from the Human Footprint Index (HFI) and the proportion of Impervious Surface Areas (ISA) - covered by buildings, roads and similar man-made structures. "We found that both ISA and HFI were positively related to the amount of anthropogenic nesting materials in the Spanish population. In contrast, there were no statistically significant correlations in the Polish population," said study final author Marcin Tobółka of the Vetmeduni's Konrad Lorenz Institute of Ethology. In addition, the researchers:in were able to demonstrate that the use of anthropogenic nesting material in Spain was twice as high as in the Polish white stork population.

Habitats: Variation in human footprint as a major factor

According to the study, the different human footprint HFI values for the Spanish and Polish study sites reflect different levels of human pressure on natural habitats. As a result, the Spanish white stork population inhabits more urbanized areas. In contrast, the Polish population remains a farmland bird and inhabits mainly areas with semi-natural meadows and pastures.

The article "The prevalence of anthropogenic nest materials differs between two distinct populations of migratory birds in Europe" by Zuzanna Jagiello, Łukasz Dylewski, José I. Aguirre, Joanna T. Białas, Andrzej Dylik, Alejandro López-García, Ireneusz Kaługa, Adam Olszewski, Joachim Siekiera and Marcin Tobółka was published in Environmental Science and Pollution Research.

Scientific article


Climate change alters bird clutches

A worldwide study with the participation of the University of Veterinary Medicine Vienna shows: Climate change has far-reaching consequences and also affects the offspring of birds - in very different ways.

Climate change influences the timing of reproduction in many bird species, but little is known about the impact on annual reproductive output. A recently published global study with the participation of the Vetmeduni now provides important new data based on a meta-analysis.

Broods become smaller on average

The research team examined long-term breeding data for the period from 1970 to 2019. A total of 201 populations of 104 bird species with 745,962 clutches on all continents were included in the study. On average, the number of offspring decreased over the last decades, but the researchers found significant differences between individual species and populations: 56.7% of the populations (significant at 17.4%) produced fewer offspring, whereas 43.3% (significant at 10.4%) had larger broods.

Some species benefit from climate change

"The results show that climatic changes influence offspring production," says co-author Marcin Tobółka from the Konrad Lorenz Institute of Ethology at Vetmeduni. In detail, the analyses indicate that rising temperatures have a negative effect especially on migratory, larger species, while sedentary species with smaller bodies might benefit from a warmer climate.

Declining number of birds is not due to smaller clutches

Since the trend towards smaller clutches is not very pronounced and is also inconsistent, the researchers assume that the rapid decline in bird populations worldwide is only to a small extent due to changes in the number of young.

The article „The effect of climate change on avian offspring production: A global meta-analysis“ by Lucyna Halupkaa, Marcin Tobółka, Konrad Halupkagg et al. was published in „PNAS“.

Scientific article


Poor visibility makes tadpoles more cautious

Low light and cloudy water are bad for vision. But how do such environmental conditions affect the behaviour of aquatic animals? A recently published study by the University of Veterinary Medicine in Vienna investigated this question using tadpoles. According to this, changing environmental conditions influence the behaviour of frog larvae - an important finding, especially because of the disturbance of many natural habitats by humans.

In their study, the international research team examined the behaviour of tadpoles of two poison dart frog species. The aim was to investigate the connection between environments with restricted vision and the individual reaction to perceived risks.

The poison dart frog species Dendrobates tinctorius - a frog with facultatively cannibalistic tadpoles - and Oophaga pumilio - whose tadpoles depend on their mother's food supply - were tested in different experimental settings. First, the general activity and space utilization of the tadpoles was measured on a black and white background, and then on either a black or white background where the tadpoles were exposed to visual cues from potential predators.

Clear and less clear effects

The effects of the original environment on the tadpoles of Dendrobates tinctorius were clear, according to study co-author Bibiana Rojas from the Konrad Lorenz Institute of Ethology at Vetmeduni: "Tadpoles that grew up in a darker original habitat were less active than tadpoles from lighter original habitats and did not respond to either of the two visual predators with increased activity. In contrast, tadpoles from a brighter source environment swam more when in the presence of potentially hostile conspecifics.” According to Rojas, this suggests that tadpoles can visually distinguish between predators. This hypothesis is also supported by the results with Oophaga pumilio: Their reactions to the two visual stimuli did not differ.

Clear proof of the influence of environmental disturbances on growing animals

A key finding of the study is that risk perception in animals is situation-dependent. In addition, the quality of light during adolescence has a significant impact on how animals respond to risk in novel contexts. "As animals are increasingly exposed to disturbed habitats, our results underscore how sensitively animals that rely on their vision respond to sudden environmental disturbances," Bibiana Rojas stresses.

Scientific article


Female scent – accelerated growth in juvenile male mice

Exposing female house mice (Mus musculus) to the scent of male urine is known to accelerate their sexual development in what scientists call the Vandenbergh effect. A recently published study led by the University of Veterinary Medicine Vienna now shows that this effect works both ways. The study found that juvenile male mice grew significantly faster when exposed to female urinary scent.

In their study, the research team tested whether exposing juvenile male mice to female urine influences their growth and the size of their sexual organs. Three-week-old male house mice were exposed to female urine daily 5x/week for about 30 minutes over a period of three months. A control group was exposed to normal water only.

Faster growth, but no influence on muscle mass or sexual organs

“We found that males exposed to females grew significantly faster and gained more body mass than control animals, despite all males being reared on the same amount of diet,” says the study’s first author, Sarah M. Zala of Vetmeduni’s Konrad Lorenz Institute of Ethology, “but we detected no differences in males’ muscle mass or sexual organs.” Exposing juvenile males to male urine had no effect on their growth. Last author Dustin J. Penn, also from the Konrad Lorenz Institute of Ethology, highlights the importance of the study: “Our results provide the first evidence to our knowledge that juvenile male mice accelerate their growth when exposed to the urine of adult females.”

Benefit without compromise: no change in immune resistance

The researchers also tested whether the males’ accelerated growth involved any functional trade-offs, where one benefit is given up in exchange for another, regarding the males’ immune resistance to an experimental infection. “We exposed juvenile male mice to a bacterial pathogen (Salmonella enterica) but found no evidence that increased growth had negative trade-offs on immune resistance to infectious disease,” says Dustin J. Penn. “Bacterial clearance, body mass or survival during infection were no different when compared to the animals from the control group.”

Underlying mechanisms still unclear

The exact mechanisms through which female urine triggers the accelerated growth response in males remains unclear, but an endocrine-mediated puberty acceleration seems conceivable. The new findings could prove useful for future studies aimed at influencing the growth or sexual development of male animals using more natural methods. According to the researchers, further studies are now needed to learn more about the mechanisms behind this effect. This would, for example, help to determine whether and how female urine exposure affects male growth and sexual development in a natural context.

The article "Female scent accelerates growth of juvenile male mice" by Sarah M. Zala, Brian Church, Wayne K. Potts, Felix Knauer and Dustin J. Penn was published in „Scientific Reports“.

Scientific article


Sexual selection alters dance moves of birds during courtship display

All dressed up and a god on the dance floor – in Saturday Night Fever, John Travolta made an impression both on the big screen and with the audience. Birds do it in a similar way, combining an attractive plumage with an acrobatic performance. The evolution of avian courtship displays was the focus of an international study conducted with the participation of researchers from the University of Veterinary Medicine Vienna using manakins, a group of birds found throughout the American tropics.

For their study, the researchers compared the elaborate courtship behaviour of two closely related species, golden-collared manakins (Manacus vitellinus) and white-collared manakins (Manacus candei), and their hybrids, focusing on a small island population of hybrids off the coast of Panama.

Courtship dance beats genetic similarity

The study confirmed that the island birds were genetically similar to the mainland hybrids, which in turn were more similar genetically to the white-collared manakin parental species. The research team then analysed the courtship dance, which is performed within an area demarcated by small saplings, which the courtship male cleans before his courtship dance (jump-snap routine).

The researchers were surprised to find that hybrid males, despite their genetic similarity to white-collared manakins, performed key dance manoeuvres like golden-collared manakins. Other elements of the hybrids’ dance performance either did not differ from that of the white-collared parents or was a mix of the courtship dance of both parental species.

Modular evolution in response to sexual selection

But why does the courtship dance of hybrid males resemble that of golden-collared manakins when the genetic background of the hybrids is more consistent with white-collared manakins? The researchers suspect that selected components of the dance routines of golden-collared manakins have been adopted by white-collared manakins through sexual selection.

Leonida Fusani, the study’s last author and head of the Konrad Lorenz Institute of Ethology at Vetmeduni Vienna, explains this process in evolutionary terms: “We hypothesise that such modular evolution occurs in response to sexual selection, whereby specific components of the bird’s dance routine shift to yield a broader change in its functional appearance.”

The article "Beyond plumage: acrobati c courtship displays show intermediate patt erns in manakin hybrids" by  Julia Barske, Matthew J. Fuxjager, Claudio Ciofi, Chiara Natali, Barney A. Schlinger, Tim Billo and Leonida Fusani was published in „Animal Behaviour“.

Video vom Balzritual

Wissenschaftlicher Artikel


Birds and biologgers – shape and position matter

Biologging devices are often attached to birds for research purposes and to collect important data. Now a team of researchers led by the University of Veterinary Medicine Vienna has investigated the aerodynamic effect of biologgers with northern bald ibis, an endangered species of bird, in a wind tunnel. The results showed that biologging devices significantly influence energy expenditure and flight distances, and that aerodynamic optimizations and proper positioning on the birds’ bodies can significantly reduce the detrimental effects.

There has been little scientific research to date regarding the impact of biologgers on animal aerodynamics and hydrodynamics. This stands in marked contrast to the increasingly extensive use of such technologies in wild-living animals. Recently, there have been growing concerns about the detrimental effects that these devices may have on the animals involved.

While the focus in biologging has long been solely on reducing weight, the researchers in this study investigated the aerodynamic effects of the devices. For this purpose, the northern bald ibises (Geronticus eremita) were trained to fly in a wind tunnel where heart rate and dynamic body acceleration (VeDBA) were measured as parameters for energy expenditure in relation to different logger shapes and wind flow directions.

The perfect biologger: attached to the back of the body and aerodynamically shaped

“Our data demonstrates that the position of biologging devices significantly influences the flight distances, and that shape has a considerable effect on energy expenditure. Unfavourable shape and positioning not merely affect the amount of energy expended during flapping flight; the energetically probably more important effect is that the devices impair the bird’s ability to glide or soar, which forces them to perform the energetically much more demanding flapping flight more frequently,” says the study’s first author, Ortal Mizrahy-Rewald from the Research Institute of Wildlife Ecology at Vetmeduni, summarizing the key findings of the study.

A complementary study with wild-living northern bald ibis during spring migration demonstrates that the position of the devices on the birds’ backs affects the length of the flight stages. “Birds that carried the devices on the upper back had significantly shorter flight stages compared to birds with a device positioned further towards the tail,” as Mizrahy-Rewald explains.

Little effort required to reduce detrimental effects

According to the researchers, the detrimental effects can be reduced with relatively little effort through a strictly aerodynamic design of the housing and increased consideration of aerodynamics when attaching the device to the animal’s body. In birds, the attachment of biologging devices via leg loops to the lower back is clearly preferable to the common attachment method via wing loops on the upper back. Nevertheless, the importance of drag reduction may vary between systems, as the benefits of having a biologging device close to the centre of gravity may outweigh the increase in drag that this involves.

The article “The impact of shape and attachment position of biologging devices in Northern bald ibises” by Ortal Mizrahy‑Rewald, Natalie Winkler, Frederik Amann, Katharina Neugebauer, Bernhard Voelkl, Herwig A. Grogger, Thomas Ruf, and Johannes Fritz was published in Animal Biotelemetry.

Scientific article


Drones and bird protection - a double-edged sword

A current international study led by the Konrad Lorenz Institute of Ethology at the Vetmeduni examined the effects of drone flights for research purposes on vultures. The researchers come to the conclusion that unmanned aerial systems offer significant advantages over other investigation methods. On the other hand, there are risks from potential disruptive effects at the breeding site of the birds of prey. The scientists therefore recommend using drones with a sense of proportion.

Vultures are among the world's most threatened bird species and play a unique role at the bottom of the food chain in ecosystems. They are therefore of great interest to science. The use of drones for research on them is developing rapidly. Reasons are technological advances, affordability and easy accessibility. However, there are a number of factors that must be taken into account when using unmanned aerial systems in order not to disturb the sensitive phase of the birds' reproduction.

An urgen need to close dangerous knowledge gaps

“The reduced disturbance of wildlife is the main argument for using modern observation and photo techniques with drones. The big unknown, however, is how animals will react and the potential for long-term negative consequences. To fill this dangerous gap, we strongly recommend documenting the use of drones with animals in captivity and in the wild. In addition, we need uniform guidelines for the use of drones in order to be able to scientifically interpret disturbances and bird reactions," says study lead author Richard Zink from the Konrad Lorenz Institute of Ethology at Vetmeduni, summarizing the most important results.

Better safe than sorry: use drones with care

Richard Zink also advocates a controlled use of drones: "Due to the lack of data on long-term disruptive effects, we advocate the precautionary principle. By following a set of species-specific recommendations, the potential negative impacts of drones can be limited and their value for conservation management maximized. In particular, the physiological and long-term effects on vulture health and reproductive success should be considered.”

Concrete recommendations to the international scientific community

According to the scientists, the high sensitivity and territorial behavior of most vulture species in particular pose considerable challenges to the use of drones. In general, the experts advise against the regular use of drones for nest inspections during the most sensitive breeding phases and in bad weather or when potential predators of the chicks are nearby. "We are not calling for a ban on the use of unmanned aerial vehicles for vulture researchers, but we expressly advocate careful examination of the circumstances and careful documentation of the effects," emphasizes Richard Zink, who is responsible for the study and together with his co-authors analyzed scientific research on the responses of European vultures and other similar species to drones.

The article "Assessing the potential disturbance effects on the use of Unmanned Aircraft Systems (UASs) for European vultures research: a review and conservation recommendations“ by Richard Zink, Elena Kmetova-Biro, Stefan Agnezy, Ivaylo Klisurov and Antoni Margalida was published in „Bird Conservation International“.

Wissenschaftlicher Artikel


Stress in salmon farming, and how to prevent it

Stefan Fischer of the  Konrad Lorenz Institute of Ethology is researching behavioural ecology and is especially interested in environmental factors that limit or facilitate social behaviour und behavioural plasticity in highly social species.  In a new project financed by the Vienna Science and Technology Fund  - WWTF, "Implementing novel feeding strategies to improve animal welfare and the release success of commercial fish farms" he will research stress in farmed salmon.

Fish farming involves the commercial breeding of fish for food production purposes or for the rehabilitation of declining natural fish populations. Thus, improving the yield and success of commercial fish farms is not only of major economic concern, but is highly relevant to the success of conservation programs. One of the most important species produced in fish farms is the Atlantic salmon, which is highly threatened in their natural habitat.

For many species bred in captivity, including fish, the availability of an unlimited supply of food is known to negatively impact the capacity to cope with stress. The success of fish farms largely depends on the production of unstressed individuals, in perfect condition to become either, high-quality food or successful re-introductions into the wild. Fish products derived from stressed individuals have a shorter shelf life, and higher levels of stress leads to low reintroduction success rates. Surprisingly, this fact is rarely considered during the commercial production of fish and very often, individuals are reared under an unlimited food supply.

In this project scientists are proposing to raise awareness of stakeholders of fish farms, to implement novel feeding strategies that consider the consequences of overfeeding. Our project has two main aims:

  1. to experimentally investigate the consequences of different feeding strategies on individual stress responses; and
  2. to improve awareness in fish farms across Sweden and Austria, that overfeeding leads to economic losses and issues in conservation programs.