Every year a small songbird, no heavier than a letter, crosses the Sahara Desert, the Mediterranean and the Arabian Desert on its migration. New research from Lund University in Sweden now reveals how the tiny bird manages this arduous journey: by flying night after night - and doing nothing during the day.
The thrush nightingale is a songbird is a long-distance traveller that arrives in Sweden in late April or early May and heads south again in August or September. They spend the winter in tropical regions, mainly in south-east Africa. In autumn, they move southwards via Egypt and east Africa. In spring, they take the journey back via the Arabian Peninsula.
Night flight saves energy
In a new study using advanced, ultra-light sensors, the researchers have been able to track the birds' behaviour during migration in detail. The results show a clear pattern. Thrush nightingales undertake four to five consecutive night-time flights, interspersed with daytime breaks where they barely move at all. In this way, the birds minimise their energy consumption during the hottest hours of the day and avoid the most intense heat in desert environments.
"This is extreme behaviour. They push themselves several nights in a row and basically shut down completely during the day," says Pablo Macías-Torres, researcher at Lund University.
Preparations before departure
The study also provides new insight into the careful preparation for the approximately 18,000-kilometre-long round migration. During their stops in desert areas, the birds, weighing in at around 25 grams - do not replenish their energy; instead, they survive on reserves built up in advance.
"These birds take no chances. Their entire strategy is based on having stored up enough energy before venturing into the most inhospitable parts of the route," says Anders Hedenström.
Improved sensor technology
Being able to track small migratory birds at this level of detail has long been a challenge. The breakthrough is due to the miniaturisation of sensor technology, which now makes it possible to study behaviour directly in free-flying individuals. The researchers have analysed eleven complete migrations from ten songbirds (captured outside Lund), both in autumn and spring over three years, providing an unusually comprehensive picture of the species' strategy.
"The next step is to understand how changing environments affect the songbirds' ability to complete the journey. This will be crucial in a world where both climate and habitats are changing quickly, concludes Pablo Macías-Torres.
Publication:
Link to the article in Biology Letters:
Migrating by night, inactive by day: ecological barrier crossing in a migratory songbird
