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Palacký University
03-16-2016, 13:04, Age: 7 y.

Extreme Performance of Small Songbirds Crossing Sahara Desert

By: Martina Šaradínová

Ornithologists conducted their research with the help of these geolocators, carried by the birds on their backs.

Small avian migrants who have to cross the Sahara Desert on their way to their wintering or breeding sites often put on heroic performance. This has been proven by an international team of ornithologists, which included representatives of the UP Faculty of Science. Monitoring of small birds weighing about 13 grammes was provided by geolocators attached to their backs. This breakthrough finding was recently published in the scientific journal Scientific Reports.

Ornithologists from the Czech Republic, Switzerland, Sweden, Finland, and Germany deployed geolocators on four songbird species – two types of flycatchers and two types of warblers, including the endangered aquatic warbler. The geolocator, weighing only 0.5 grammes, monitors the intensity of daylight, from which the length of day and the time of sunrise and sunset can be estimated. On the basis of such data, scientists are able to reveal where the bird is situated. This time, researchers focussed on how fast and in what manner the vast barrier of desert with its inhospitable conditions is overcome by the small avian migrants.

“When these small birds depart their European breeding grounds at the end of summer, they usually fly overnight and rest in the daytime. Once they reach the Mediterranean Sea and the subsequent Sahara Desert, many of them switch to a nonstop regime, maintaining flight across the entire distance. Considering that these birds weigh some 12 or 13 grammes and that their flight over the Sahara Desert takes approximately 50 hours, it is an incredible performance. It denies, to certain extent, the existing knowledge on the physiology and capabilities of these animals,” said one of the co-authors, Peter Adamík from the Department of Zoology.

All 34 monitored birds however did not behave identically. Only a few individuals decided to take solely nocturnal flights, hiding from the heat in the day. Most birds, on the contrary, tried to cross as long a passage as possible, extending their nocturnal flights into the day. One of the factors was also which part of the Sahara Desert they were crossing. The width of its western part is over one thousand kilometres, whereas in the Central Sahara, roughly double the distance has to be covered. “The larger travel distance over the desert they had to cover, the longer the flight duration. So they were capable of being flexible, adapting to the conditions. They interrupt their flight only in an environment that allows them to find food and regain strength. For example, some organs decrease in size, while they must put on extreme weight, in order to build up their body fat reserve,” explained Adamík.

According to him, this study is ground-breaking, since such information on small migrant birds has been missing. Until now, ornithologists have only monitored the extremely long flights of bigger birds; smaller species could be monitored only by recently developed light-level geolocators. “The opinions on how the small songbirds cross the Sahara have varied to date. But we have found an answer. Nonetheless we also show that avian behaviour tends to be variable. The majority of monitored birds however tried to fly as long as possible in one go. For such small birds it is truly a heroic performance,” concludes Adamík.

Although it has been known that birds usually migrate faster in the spring than in the autumn, they need the same amount of time to cross the Sahara in both cases. This finding also confirms the fact that their crossing of this territory requires their maximum performance.

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Last update: 19. 09. 2012, Vladimír Kubák