Even small migratory birds rely on gliding flight

Study: Bee-eaters do not slow down while sailing and save even more power reserves than larger species

European Bee-eater © Itai Shanni
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Large migratory birds such as storks save on their flight power reserves by sailing on thermal currents. For smaller migratory birds, this behavior was previously unknown. However, scientists have now discovered that species such as the European bee-eater Merops apiaster sometimes fly in gliding flight.

These little birds will not slow down and save even more power reserves than larger species, the researchers write in the journal "PLoSOne".

When we think of birds that glide majestically through the air without a flapping wing, we imagine large species such as the white stork or a bird of prey in search of food. These flight patterns of large migratory birds have already been closely studied. Ornithologists know a lot about their airspeed, the distances covered and the proportion of different flying techniques during the turn.

European Bee-eater in the sights

In smaller birds they took a long time, they could not slide because of their low muscle strength and the smaller wings in the same extent and save power reserves. The gliding flight reduces the speed compared to the flight with continuous wing beat, so the assumption.

Scientists from the Ben-Gurion University of the Negev, the University of Jerusalem and Martin Wikelski from the Max Planck Institute for Ornithology in Radolfzell have for the first time examined the energy consumption of small migratory birds in the field. They caught a few specimens of the European bee-eater in Israel and attached small transmitters on their backs. display

Bee-eater in flight © Jorge Rodrigues

Energy expenditure determined

With the sensitive devices, they were able to measure every wing beat, heart rate and airspeed. In order to determine the energy expenditure, the researchers determined in the laboratory that the heart rate of the birds is an indicator for the oxygen consumption and that the measured values ​​draw conclusions about the energy consumption Allow during the flight.

In the evaluation of the measurement results, we were surprised to see that the bee-eaters frequently switched between gliding and rudder-flying and that, moreover, the heartbeat frequency during gliding was only half as high, says Wikelski. The birds need as little energy when gliding as when resting on a branch or in the nest.

Significantly higher energy savings

In previous studies on larger migratory birds, however, a 30 percent higher heart rate was measured during gliding than when resting. This flying technique therefore represents a much greater saving of energy for small migrating birds than for larger species. Even a loss of speed could not be determined.

According to the scientists, the result of this study answers not only the question of whether small train birds can sail or glide during their long journey: they are even as fast and use less power reserves.

(Doi: 10.1371 / journal.pone.0013956)

(Max Planck Institute for Ornithology, 08.12.2010 - DLO)