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Gut hormones prepare birds for migration

The long seasonal travels of migratory birds are a well-known phenomenon. But what hormonal processes are involved? A recent study by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine Vienna identifies sharply rising levels of the hormone ghrelin as a key trigger of migratory restlessness. The recently published research could not, however, confirm a connection with the hormone corticosterone as shown in other studies.

Migratory birds have spectacular physiological adaptations to accommodate the long-distance flights between their breeding and wintering grounds. The animals use fat reserves built up prior to migration as their main source of energy. In both captive and free-flying birds, the migratory phenotype – the physical changes that occur prior to and during migration – is signalled by rapid and marked increases in food and energy intake as well as by changes in nocturnal activity and by migratory restlessness. However, there has been little scientific evidence to date on the exact hormonal mechanisms underlying this process.

Hormone ghrelin makes quail fit for long flights

An international research team led by the Konrad Lorenz Institute of Ethology at the University of Veterinary Medicine used common quails (Coturnix coturnix) to assess if  the hormone corticosterone and the gut-derived hormone ghrelin play a role in the seasonal expression of migratory behaviour. For their experiment, the researchers exposed quails to controlled changes in day length  to simulate autumn migration, followed by a wintering period. The researchers then compared corticosterone and ghrelin concentrations and assessed whether these two metabolic hormones varied between migratory states.

“In accordance with our predictions, we found that the emergence of the migratory phenotype was associated with higher concentrations of ghrelin. In addition, ghrelin correlated with changes in body mass of birds as they transitioned into their autumnal migratory state and as they entered the wintering state,” explains the study’s first author, Valeria Marasco from the Konrad Lorenz Institute of Ethology at Vetmeduni.

No correlation between corticosterone levels and migratory restlessness

Contrary to their predictions, however, the researchers observed no correlation between circulating levels of ghrelin and corticosterone. The scientists were also unable to detect elevated levels of corticosterone in the migratory phenotype. “There was no significant correlation between baseline corticosterone levels and changes in body mass, levels of food intake or migratory restlessness (the urge of captive birds to migrate at night)” says the study’s senior author Leonida Fusani, head of the Unit of Ornithology at the Konrad Lorenz Institute of Ethology.

The article "Ghrelin, not corticosterone, is associated with transitioning of phenotypic states in a migratory Galliform“ von Valeria Marasco, Hiroyuki Kaiya, Gianni Pola, and Leonida Fusani was publised in „frontiers“.


Scientific article



VetmedTalk „Grüne Lungen“ (Green lungs). People and animals in forest ecosystems

 (Talk in German)

VetmedTalk: Heute verstehen. Morgen verändern.


12 December 2022 | 5-6 p.m. | Online 

Sometimes you can't see the forest for the trees: Countless details block the view of the big picture. With this VetmedTalk, the University of Veterinary Medicine, Vienna, together with the experts from the Donauauen National Park and the Austrian Federal Forests, wants to offer a comprehensive overview of the special features of the forest habitat. For a healthy future for animals and humans, we need a healthy forest.

Austria is a densely wooded country: 3.5 billion trees cover almost 50 percent of the national area and form a diverse habitat for a wide variety of animals. Deer and rabbits, foxes and hedgehogs, but also many birds, insects, amphibians and reptiles make the forests a unique ecosystem. The VetmedTalk "Green Lungs" presents exciting research projects from veterinary medicine and examines how the health of animals and the health of humans are related through the forest habitat.

Forests are essential for us humans. They produce oxygen for our air, wood for our furniture, store our drinking water, prevent floods and protect against mudslides and avalanches. We use the "green lungs" in our free time as a place to relax, and as a huge carbon store, they are also an important instrument in climate protection. At the same time, the forest is a habitat for countless animal species, flora and fauna in the forest are essential for a healthy environment. Nevertheless, we humans have a massive impact on the life of these forest ecosystems through climate change and intensive forest use.

How can humans and animals coexist and thrive in the forest? And what can veterinary medicine contribute to climate protection and biodiversity?

In 2022, the Vetmeduni will focus on communication on "Life on land", UN Sustainable Development Goal No. 15, with a special habitat focus each quarter. It started with air, followed by fresh water and meadows , and the forest ecosystem now concludes the series. The last VetmedTalk of this year is about the status quo of our forest dwellers and how we can protect their habitat. Science communicator Bernhard Weingartner and his guests will answer questions from the online audience.


  • Claudia Bieber, Research Institute of Wildlife Ecology, Vetmeduni
  • Edith Klauser, Nationalpark Donauauen
  • Alexandra Wieshaider, Austrian Federal Forests
  • Richard Zink, Konrad Lorenz Institute of Ethology, Vetmeduni


  • Bernhard Weingartner, Science communicator and initiator of the Science Slam Austria


Live online stream at



The sex lives of birds

Banding together may pay off for subordinate males

Male spotted bowerbirds (Ptilonorhynchus maculatus) build and defend a structure of sticks and straw - the bower. They decorate these nests with colourful objects to attract mates during the breeding season. Certain non-resident subordinate males are tolerated by resident males in their bowers over multiple breeding seasons. Previous research has shown that these male coalitions bring indirect benefits to subordinate males. So far, however, it has been unclear whether lower-ranking males also have direct advantages. A current study by the Konrad Lorenz Institute of Ethology of the Vetmeduni shows for the first time that in rare cases the lower-ranking birds benefit directly from copulation opportunities.

The study documents four cases of sneaky matings or mating attempts by subordinate males. The cases were observed in the bowers of spotted bowerbirds during the 2018 breeding season. Several non-resident males disrupted ongoing copulations between the bower-owner and a receptive female, and these events were followed by vigorous aggressive interactions. "These observations shed new light on same-sex social dynamics in bowerbirds and support the hypothesis that subordinate males are sexually mature individuals who occasionally gain access to females while visiting established bowers," said study first author Giovanni Spezie of the Konrad Lorenz Institute of Ethology at the Vetmeduni.

First observation of extremely rare events

The rarity of the events now observed is remarkable. Extensive observations have been made on spotted bowerbirds for several decades - but so far, none of the observed copulation events has been documented. Study lead author Leonida Fusani from the Konrad Lorenz Institute of Ethology at Vetmeduni: “The fact that we were able to record at least four independent observations in different individuals strongly indicates that sneaky copulations are not an isolated and abnormal behaviour. Rather, it is a behavioural pattern or alternative reproductive strategy used by subordinate males.”

Beta profits from Alpha – male coalitions are profitable

Male-male coalitions have so far been observed particularly in birds such as manakins, grouse, peacocks, wild turkeys and bowerbirds. A common feature of most courtship coalitions is that a dominant "alpha" male accounts for all or most copulations, while subordinate "beta" males abstain from breeding and have no—or very limited—access to mates. Sacrificing reproductive potential for a male association may seem paradoxical, but it has direct and indirect benefits for the subordinate males. The animals benefit indirectly, for example, from taking over the position of the alpha male after his death or from learning behaviour that is important for successful mating from him. As it turns out, they also derive direct benefits from clandestine mating with females.

The article "Sneaky copulations by subordinate males suggest direct fitness benefits from male-male associations in spotted bowerbirds (Ptilonorhynchus maculatus)“ by Giovanni Spezie and Leonida Fusani was published in „Ethology“.

Scientific article



Measuring brain size in birds: Which parameters are best?

Do bigger heads necessarily mean bigger brains? The study of brain size (as a proxy for cognitive ability) is rather difficult in wild animals, and scientists have tried to find ways to measure brain size without harming the animals. Head size has been used in the past and seems to work for some species – but not for all. In a study on quails by Vetmeduni scientists and researchers from Poznań University of Life Sciences, Poland, researchers found that it was head height, rather than overall head volume was a better predictor of brain size, However, it turns out that every species is different and needs to be assessed separately.

At least in part, the brain’s capacity to process cognitive processes depends on the mass of neural tissue involved – the more tissue, the more information can be processed. In fact, studies often find a positive relationship between brain size and cognitive performance. However, the majority of these studies are based on comparisons between different species. A growing number of scientists is now trying to understand how more subtle differences between individuals of the same species are related to their cognitive skills, which is often a big challenge when studying animals in nature. To do so researchers require techniques that do not interrupt the natural life cycle of wild birds.

A first study of barn swallows proposed to use external head measurements, which require handling but not the sacrifice of the individual bird, as an accurate approximation for brain mass.

A team of researchers from the Konrad Lorenz Institute of Ethology (KLIVV) of the Vetmeduni, together with researchers from Poznań University, Poland employed this method for the first time in a small Galliform, the Common Quail. They measured both the external head dimensions of the birds as well as the weight of their brains and tested how well these two measurements were related to each other.

Head height is crucial

Although the scientists found that these measurements were correlated, the correlation values were not very strong. This means that external head measurements really cannot be used reliably to predict an individual’s brain mass with high confidence. Instead, the best predictor of brain mass was not head volume per se, as was previously shown in barn swallows, but the height of the head alone.

“Our results show that the model that explained the highest proportion of variance in brain mass contained only one head measurement, the head height,” says Valeria Marasco, one of the two first authors of the study. “Nevertheless in our study species, the Common quail, this measure explained only a small proportion of the variance in brain mass of different birds. Studies on other species have found a much more significant effect of one or the other variable.”

It is likely, therefore, that other factors also explain the variation. “For example, average beak lengths in different species could influence head measurements,” says Joanna Białas, joint first author of the study. Interestingly, brain size was not at all related to body mass or length of the bird overall. Brain size has evolved from other aspects of an animal´s morphology.

The researchers recommend validating the original method of external head measurements in each avian species before making assumptions on how these measurements might be related to brain size and cognitive performance. More studies across diverse bird species are also needed to elucidate potential relationships between relative brain size, body parameters, and sex.

The article “Are external head measurements a reliable predictor of brain size in the Common Quail (Coturnix coturnix)?” by Joanna T. Białas, Valeria Marasco, Leonida Fusani, Gianni Pola, and Marcin Tobółka was published in the Canadian Journal of Zoology.

Scientific article