TUESDAY, 21 DECEMBER 2010
An international team of researchers has disproved this assumption by tracking migrating European bee-eaters, using radio transmitters attached to the birds’ backs. European bee-eaters weigh approximately 55g, and yet it was found that they often switched between flapping and soaring-gliding during their journey. Using heart rate as an indication of energy consumption, soaring-gliding was also found to allow much greater energy savings for these smaller birds than for larger species. Herring-gulls weighing 0.9kg, for example, are known to use 30% more energy when soaring-gliding than when they are resting, whereas the bee-eaters used the same amount of energy when soaring-gliding as when they were at rest in their nests.
The results of this study not only show that small birds, surprisingly, tend to soar-glide when migrating, but also indicate that soaring-gliding is even more energetically favourable for smaller birds than for larger species.
Written by Katy Wei Evidence gathered from large birds has shown that ‘soaring-gliding’ flight is much more energy efficient than flapping their wings. Until recently, however, it was thought that for smaller species soaring-gliding flight would not be advantageous compared to wing-flapping. A smaller musculature and wing structure was thought to mean that their flight speeds when soaring-gliding would be much less than when they were flapping their wings, and so a prolonged flight time would incur a high cost in terms of fitness. Scientists therefore believed that birds weighing below 0.9kg would always preferentially fly by flapping their wings when migrating.