Concept: Dynamic soaring
Albatrosses do something that no other birds are able to do: fly thousands of kilometres at no mechanical cost. This is possible because they use dynamic soaring, a flight mode that enables them to gain the energy required for flying from wind. Until now, the physical mechanisms of the energy gain in terms of the energy transfer from the wind to the bird were mostly unknown. Here we show that the energy gain is achieved by a dynamic flight manoeuvre consisting of a continually repeated up-down curve with optimal adjustment to the wind. We determined the energy obtained from the wind by analysing the measured trajectories of free flying birds using a new GPS-signal tracking method yielding a high precision. Our results reveal an evolutionary adaptation to an extreme environment, and may support recent biologically inspired research on robotic aircraft that might utilize albatrosses' flight technique for engineless propulsion.
Animal movement is a fundamental eco-evolutionary process yet the behaviour of juvenile animals is largely unknown for many species, especially for soaring seabirds which can range widely over the oceans at low cost. We present an unprecedented dataset of 98 juvenile albatrosses and petrels (nine species), tracked for the first three months after independence. There was a startling diversity within and among species in the type and scale of post-natal movement strategies, ranging from area-restricted to nomadic patterns. Spatial scales were clustered in three groups that ranged from <3000 km to >6000 km from the natal nest. In seven of the nine species, the orientation of flight paths and other movement statistics showed strong similarities between juveniles and adults, providing evidence for innate orientation abilities. Our results have implications for understanding the development of foraging behaviour in naïve individuals and the evolution of life history traits such as survival, lifespan and breeding strategy.
Albatrosses and other large seabirds use dynamic soaring to gain sufficient energy from the wind to travel large distances rapidly and with little apparent effort. The recent development of miniature bird-borne tracking devices now makes it possible to explore the physical and biological implications of this means of locomotion in detail. Here we use GPS tracking and concurrent reanalyzed wind speed data to model the flight performance of wandering albatrossesDiomedea exulanssoaring over the Southern Ocean. We investigate the extent to which flight speed and performance of albatrosses is facilitated or constrained by wind conditions encountered during foraging trips.
- Philosophical transactions of the Royal Society of London. Series B, Biological sciences
- Published almost 4 years ago
While prior studies of swallow manoeuvering have focused on slow-speed flight and obstacle avoidance in still air, swallows survive by foraging at high speeds in windy environments. Recent advances in field-portable, high-speed video systems, coupled with precise anemometry, permit measures of high-speed aerial performance of birds in a natural state. We undertook the present study to test: (i) the manner in which barn swallows (Hirundo rustica) may exploit wind dynamics and ground effect while foraging and (ii) the relative importance of flapping versus gliding for accomplishing high-speed manoeuvers. Using multi-camera videography synchronized with wind-velocity measurements, we tracked coursing manoeuvers in pursuit of prey. Wind speed averaged 1.3-2.0 m s(-1) across the atmospheric boundary layer, exhibiting a shear gradient greater than expected, with instantaneous speeds of 0.02-6.1 m s(-1) While barn swallows tended to flap throughout turns, they exhibited reduced wingbeat frequency, relying on glides and partial bounds during maximal manoeuvers. Further, the birds capitalized on the near-earth wind speed gradient to gain kinetic and potential energy during both flapping and gliding turns; providing evidence that such behaviour is not limited to large, fixed-wing soaring seabirds and that exploitation of wind gradients by small aerial insectivores may be a significant aspect of their aeroecology.This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’.
Dynamic soaring is a small-scale flight manoeuvre which is the basis for the extreme flight performance of albatrosses and other large seabirds to travel huge distances in sustained non-flapping flight. As experimental data with sufficient resolution of th ese small-scale movements are not available, knowledge is lacking about dynamic soaring and the physical mechanism of the energy gain of the bird from the wind. With new in-house developments of GPS logging units for recording raw phase observations and of a dedicated mathematical method for postprocessing these measurements, it was possible to determine the small-scale flight manoeuvre with the required high precision. Experimental results from tracking 16 wandering albatrosses (Diomedea exulans) in the southern Indian Ocean show the characteristic pattern of dynamic soaring. This pattern consists of four flight phases comprising a windward climb, an upper curve, a leeward descent and a lower curve, which are continually repeated. It is shown that the primary energy gain from the shear wind is attained in the upper curve where the bird changes the flight direction from windward to leeward. As a result, the upper curve is the characteristic flight phase of dynamic soaring for achieving the energy gain necessary for sustained non-flapping flight.