What is the relation between hormones and bird migration?

In her PhD, Juliana da Costa Araújo investigates whether hormones influence changes in the behavior of a South American bird throughout the seasons.

High body temperature, feathers, oil and shivering: those are ways how birds living in cold climates manage to survive the winter. Their feathers help them conserve heat coming from their own bodies by keeping a layer of warm air between them. They maintain a body temperature around 40°C. Many species produce an oil to preserve their feathers and make them waterproof. Others shiver, moving their muscles involuntarily to produce heat. Despite all these adaptations, it is very difficult to maintain this energy when food is scarce, such as winter. Therefore, many other species adapt to these natural climatic fluctuations by migrating to warmer regions.

This is the case of the little bird white-crested elaenia (Elaenia chilensis). This South American native species travels from North to South on the continent in search of more favorable conditions to its survival. When it is summer in the southern hemisphere, the birds inhabit a more southern region of the continent, and are often found in Chile (hence the name of their species) and Argentina. When the weather cools down, these birds go in search of warmer temperatures, travelling around 6,000 km to find the ideal shelter in Brazil.

The white-crested Elaenia (Elaenia chilensis), a South American migratory bird. Photo by Rigoberto Yáñez, published in the Avibase platform.

The little Elaenia birds certainly perceive changes in weather and food availability during the seasons. But how this external information is processed by their brains, leading them to migrate? Is there something that changes in the brains of these animals that correlates with these external changes? These were the initial questions that motivated Juliana da Costa Araújo’s PhD project.

The scientist’s bet is that at least one of the explanations for these questions lies in hormones. These are molecules produced by specialized cells, usually part of endocrine organs. When they are ready, they are released into the blood in order to send a message to another part of the body. “It is as if the hormones were on a bus traveling to their workplace. When it arrives at the correct place, the hormone gets off the bus and goes to work at the place it arrived,” Juliana explains.

“In my case, the place that the hormones will act is the brain. But for the hormone to get into the brain, it has to prove that it is itself and not another foreign [substance]. Each hormone has a unique appearance. It is as if it has a special key to get into the right place and start working, and this key has to fit into the lock just right. This lock is called a receptor, and each hormone is identified by this receptor to make sure that only the right hormone gets in there,” continues the scientist. And in her work she tries to find out where and how many locks for certain types of hormones are located in the brain of the little guaracava bird. Since her study is still in progress, the identity of these hormones cannot yet be disclosed.

With her research, Juliana wants to understand if there are any changes in the brains of guaracavas from one season to the next. Her hypothesis is that hormones may be behind changes in the birds’ behavior between seasons, such as migration. And, to test this hypothesis, she studies whether there are any differences in the types and amounts of hormones and their receptors throughout the year: “I compare these receptors at different times of the year (e.g., Spring and Summer) and make a description of these differences,” she explains.


Distribution of the white-crested Elaenia in the world, in lilac, according to the eBird platform.

In addition to analyzing how the small Elaenias adapt to normal environmental fluctuations between seasons, studies like Juliana’s can also help understand how these little birds are affected by climate change. If these birds migrate over such large distances, it is reasonable to think that environmental impacts such as global warming would greatly affect their habitats and, consequently, these birds. Therefore, over time, by comparing studies like Juliana’s with others produced at different periods, one can get an idea of the impacts of these global temperature changes on this species.

And her research is also quite relevant for studying a species that is not commonly explored in academia. “Most neuroscience studies have been done on model animals, that is, few species and animals used in captivity. In this way, it is not possible to have a broader understanding of the brain and its evolution that is closer to reality. The study becomes particularly important for animals outside the places of major scientific focus, such as North America and Europe,” adds Juliana.


Juliana’s routine is divided between being in the lab and doing field work.

Most neuroscience studies have been done on model animals, that is, few species and animals used in captivity. In this way, it is not possible to have a broader understanding of the brain and its evolution that is closer to reality. The study becomes particularly important for animals outside the places of major scientific focus, such as North America and Europe.

And just like her research subject, the scientist has moved quite a lot in search of different opportunities. The Brazilian scientist, from Natal, graduated in Biology at the Federal University of Rio Grande do Norte (UFRN), in Natal. During her undergraduate studies, she spent a year and a half at University of Lethbridge, in Canada, sponsored by the Science Without Borders program. After graduating, she returned to Lethbridge to pursue a Master’s degree in Neuroscience and did an internship at Cornell University in the United States. And today she does her PhD in Biology at Max Planck Institute for Ornithology and at the University of Konstanz, both in Germany.

And in her doctoral project it has not been different. To collect samples of white-crested Elaenias she embarked on an adventure toward Argentinian Patagonia. There, she lived for five months in Esquel, part of one of the least populated regions of the country. In a mixture of amazement, excitement and exhaustion, her routine involved, among other things, opening trails, collecting samples, and observing the behavior of the birds. Besides the intense workload, many challenges came along the way: there were forest fires, there was a lack of material to preserve the samples, and, on top of that, it was her first experience coordinating research assistants. But she says that without the help and hospitality of the Argentinians everything would have been even more difficult.


Juliana in Esquel, Argentina, collecting samples for her project.

Her passions for adventure and nature don’t stop at work. In her leisure time, Juliana enjoys outdoor activities such as hiking, kitesurfing, and scuba diving. When asked what inspired her to become a scientist, she recalls her eighth grade Biology teacher, Solange: “She was passionate about the field and that was important to me.” Being a very curious person, the researcher believes that her profession is quite stimulating for her: “Having a job that allows me to answer my own questions is something that motivates me a lot,” she explains.

Thank you, Juliana, for sharing your story with us. May your curiosity, adventurous spirit, and passion for nature continue to inspire you. You will go far!

You can continue to follow Juliana’s career here.

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