Flight

The subject of animal flight in the Malay Peninsula and Borneo has been investigated primarily through quantitative biometric studies, with the most substantial contribution to the regional literature being a 1930 paper by E. Banks, Curator of the Sarawak Museum, which tested the mathematical relationship between body weight and wing area across birds, bats, and insects using specimens collected during four years of comparative isolation in Borneo [1, p. 334].

Scope and Historical Definition

Banks’s study drew on approximately 123 species of birds, 40 of bats, and 186 of insects collected for the Sarawak Museum, and was designed to extend the earlier German work of Mullenhoff (1885), who had measured 192 specimens of 88 bird species, 12 bats, and 75 examples of about 50 insect species [1, p. 335]. A key methodological distinction was Banks’s decision to measure wing area exclusively, excluding the surface area of head, body, and tail that earlier observers such as Mullenhoff and Harting had included; this prevented direct numerical integration of his data with prior European measurements [1, p. 335]. The central thesis was that the ratio of wing area to body weight follows a predictable inverse relationship, and that the cube root of this ratio approximates a near-constant value of about 4, a property that Banks and his advisor Prof. Huxley argued was primarily geometrical rather than biologically determined [1, pp. 334–336].

Quantitative Findings and Taxonomic Variation

Banks’s graphs, compiled from his own measurements and from Mullenhoff’s data, showed that relative wing area decreases very sharply at first as weight increases, then decreases more gradually in middle weights, and shows very little change as maximum weights are reached [1, p. 335]. The “constant” ³√(Wing Area/Weight) ranged from 5.8 to 2.8 in birds and bats, and from 12.6 to 1.6 in insects, clustering mostly between 6 and 3 [1, p. 336]. Many insects had a much greater relative wing area than birds, the ratio reaching approximately 300 in some of the former but not more than 10 in the latter [1, p. 337]. Among birds, strong, swift, direct fliers such as ducks, partridges, pheasants, waders, and pigeons had the lowest relative wing areas and the fewest light species [1, p. 337].

Several exceptions were noted. The Argus Pheasant (Argusianus grayi) had an inflated wing area owing to the enlargement of its secondary wing feathers as a secondary sexual character, while the Nightjar, Frogmouth, and Giant Swift were identified as unexplained outliers among Piciform birds [1, p. 337]. The male Flying Fox was typically heavier than the female but had about the same wing area, which Banks interpreted as an adaptation to the female’s increased weight when carrying young [1, p. 337]. Mullenhoff’s flying fish data placed them below any order of birds on the relative wing area scale, suggesting they were gliders rather than flappers [1, p. 337].

Gliding and Non-Flapping Locomotion

Banks included measurements of gliding mammals and reptiles alongside true fliers. The Flying Squirrel (Iomys thomsoni) and the Flying Lemur, both gliders, fell rather low on the relative wing area scale, while flying lizards (Draco sp.) had a ratio of wing area to weight of about 5, placing them surprisingly high among birds despite only gliding [1, pp. 337]. This distinction between gliding and flapping locomotion was a recurring theme in the comparative data.

Research and Documentation

The Society’s literature on animal flight is represented by a single substantial quantitative study. Banks’s 1930 paper is notable for providing the first large-scale dataset of wing-area measurements from a tropical fauna and for introducing the methodological refinement of measuring wing area exclusively [1, p. 335]. The paper explicitly frames Banks’s four years of “comparative isolation” in Borneo as a constraint on access to existing literature, positioning the work as a contribution made from the periphery of the European scientific establishment [1, p. 334]. Banks acknowledged that his German was insufficient to do full justice to Mullenhoff’s original article, which he described as inaccessible and containing much more on other aspects of flight [1, p. 338]. The study’s advisors included Prof. J. S. Huxley, who suggested the method of grouping by weight and plotting separate curves for each order, and Prof. H. Levy, who addressed the mechanical and mathematical possibilities of the analysis [1, p. 338].

MBRAS Sources

• E. Banks (1930). The relation of weight to wing area in the flight of animals. JMBRAS 8(2): 334–360

References

1. E. Banks (1930). The relation of weight to wing area in the flight of animals JMBRAS 8(2): 334–360.