The flight of petrels and albatrosses (procellariiformes), observed in South Georgia and its vicinity

Abstract

Nine procellariiform species, covering a range of body mass exceeding 200: 1, were studied during a visit to Bird Island, South Georgia, with the British Antarctic Survey, in the 1979-1980 field season. Speed measurements were made by ornithodolite of birds slope-soaring over land, birds flying over the sea but observed from land, and birds observed from a ship. In the second group, which showed the least anomalies, lift coefficients corresponding to mean airspeeds were about 1 for albatrosses, decreasing to about 0.3 for the smallest petrels. All species increased speed when flying against the wind. The small species proceeded by flap-gliding, while the large ones flapped infrequently, and only in light winds. The small species flew lower than the larger ones, but this may be related to the fact that most of the observations were of birds flying into wind. The albatrosses ( Diomedea, Phoebetria ) and giant petrels ( Macronectes ) were found to have a ‘shoulder lock’, consisting of a tendon sheet associated with the pectoralis muscle, which restrained the wing from elevation above the horizontal. This arrangement was not seen in the smaller species, and was interpreted as an adaptation reducing the energy cost of gliding flight. The main soaring method in the large species appeared to be slope-soaring along waves. Windward ‘pullups’ suggestive of the classical ‘dynamic soaring’ technique were seen in large and medium-sized species. However, the calculated strength of the wind gradient would have been insufficient to maintain airspeed to the heights observed, and it was concluded that most of the energy for the pullups must come from kinetic energy, acquired by gliding along a wave in slope lift. Gliding downwind through the wind gradient should significantly increase the glide ratio, but this was not observed. Slope-soaring along moving waves in zero wind was recorded. The data were used to derive estimates of the average speeds that the different species should be able to maintain on foraging expeditions. Estimates of the rate of energy consumption were also made, taking into account the greater dependence on flapping in the smaller species, and on soaring in the larger ones. The distance travelled in consuming fuel equivalent to a given fraction of the body mass would seem to be very strongly dependent on mass. Comparison of the largest species ( Diomedea exulans ) with the smallest ( Oceanites oceanicus ) suggests that ‘range’, defined in this way, varies as the 0.60 power of the mass, although the relation is more complex than a simple power function.

Flight paths of seabirds soaring over the ocean surface enable measurement of fine-scale wind speed and direction

“…3A), which has several possible explanations. First, satellite-based wind speed is extrapolated to a 10-m reference height, whereas the average flight height of studied birds is below 10 m: ∼2 m for shearwaters and 3-8 m for albatrosses (28). This difference in height is suspected to be one of the cause of the underestimation of bird-based wind speed due to the shear of wind speed decreasing near the ocean surface.…”

Flight performance of the largest volant bird

“…Wandering Albatrosses (D. exulans) use a tendinous shoulder lock to hold the wing in a horizontal position (28) and dynamic soaring near the boundary layer above waves to achieve metabolically efficient flight. Frigatebirds pursue a different strategy, taking advantage of ascending air currents to maintain high altitudes and occasionally descending to the surface to exploit patchily distributed feeding opportunities (29).…”

Foraging energetics of Grey‐headed Albatrosses Diotnedea chrysostoma at Bird Island, South Georgia

“…However, the lower flight (and hence also at-sea metabolism) costs of Grey-headed Albatrosses is not unexpected considering the species' flight adaptations. Albatrosses are renowned for their ability to glide for long periods without a wing beat, utilizing specialized techniques (Pennycuick 1982(Pennycuick , 1986. In addition to the basic structural adaptations for this characteristic gliding flight, albatross energy costs are further reduced by a morphological adaptation (specifically a tendinous 'wing-lock') holding the wing in a gliding position without involving the use of musculature (Pennycuick 1982).…”

“…Albatrosses are renowned for their ability to glide for long periods without a wing beat, utilizing specialized techniques (Pennycuick 1982(Pennycuick , 1986. In addition to the basic structural adaptations for this characteristic gliding flight, albatross energy costs are further reduced by a morphological adaptation (specifically a tendinous 'wing-lock') holding the wing in a gliding position without involving the use of musculature (Pennycuick 1982). Analysis of their flight dynamics suggests that they are among the most economical of flying birds; the values for flight energy costs reported here are entirely consistent with this view.…”

“…Although field studies of energy expenditure have been carried out on a variety of birds and mammals (e.g., Mullen 1970, Utter & Lefebvre 1972, Shoemaker et al 1976, Bryant & Westerterp 1983, little attention has been given to species adapted for long-distance travel. Of birds, pelagic seabirds of the Order Procellariiformes contain many such species and pre-eminent amongst these, in terms of specializations for economy of long-distance flight, are the albatrosses Diomedeidae, which are essentially dependent on soaring and gliding (Pennycuick 1975(Pennycuick , 1982(Pennycuick , 1986. T h e metabolic rate during free-ranging gliding flight has not yet been estimated for any bird; the energy costs of foraging trips have not been measured for any procellariform and there is only one previous study of a seabird, the Sooty T e r n Sterna fusrata (Flint & Nagy 1984).…”