An Estimated Weight of the Largest Known Bird

Dean Amadon
1947 The Condor  
The Ostrich (Struthio camelus), largest of living birds, was far surpassed in size by the Elephant-bird (Aepyornis madmus) of Madagascar. The larger of the New Zealand moas such as Dinornis were intermediate in size. The moas and elephant-birds were exterminated by the natives of these islands and are known only from sub-fossil remains of skeletons, eggs and feathers. An estimate of the weight of the largest known birds may be of both scientific and popular interest. Although the living ratites
more » ... the living ratites may not be closely related to tlie extinct ones of Madagascar and New Zealand, they are the closest approach to them in size and proportions, and may be used as a basis for calculations. This study was undertaken at the suggestion of Dr. Ernst Mayr, and he has given me a number of valuable suggestions. MATERIALS AND MEASUREMENTS The species used in this study are as follows: Aepyomithidae. Elephant-birds: AepyorJs maximus, Mullerornis agilis. Dinornithidae. Moas: Dinornis maximus, D. giganteus, Euryapteryx sp. The two species of Dinornis were probably geographical representatives on the two principal islands of New Zealand. The skeleton of EuryaPteryx which was examined, according to Oliver' s (1930) key, would represent E. pygm&& _ Apterygidae. Kiwis: Apteryx sp. Casuariidae. Cassowaries: Measurements of the small species, C. bennetti, were not used. Most of the measurements availahle for the larger cassowaries (C. casuarius and C. unctppendicu-Z&us) were not identified to species and were combined. Dromaeidae. Emus: Dromaeus n. hollandiae. Rheidae. Rheas: Rhea americana. Struthionidae. Ostrich: Struthio cam&~. The Casuariidae and Dromaeidae belong to the same order. The Apterygidae are related to the Dinornithidae, though less closely. Except for these, the families listed above are believed to be no more closely related to each other than to various orders of flying (carinate) birds. Measurements used are as follows: Body length, measured from the anterior border of the thorax to the center of the acetabulum. Although this measurement falls on a diagonal, it seemed most satisfactory of several tried while seeking an over-aJ1 measure of general body size. In Aepyornis and Mulkrornis this measurement was &mated from photographs of articulated skeletons published by Monnier (1913) and Lamberton (1934), respectively, by taking a ratio between body length and a known measurement such as the tibiotarsus. Femur area, the area of the cross section of the femur calculated from its circumference measured at its smallest point near the center of the shaft. Egg weight, the approximate weight in kilograms. In a previous paper (Amadon, 1943a) I have summarized earlier formulas which show that the volume of an egg in cubic centimeters is roughly equal to one-half its length times its breadth squared (0.5 LBP) , measurements being to the nearest centimeter. This calculation also corresponds approximately to the weight of the egg in grams, since the specific gravity of a fresh egg is about 1. As interest for present purposes is in relative rather than absolute egg weights, use of this formula is satisfactory. Real errors in relative egg weights result from differences in egg shape (for example, the egg of the Ostrich is rounder than those of other living ratites), but it would be difficult to work out a compensation for this error. Limb bones, the over-all length of the bones. The flaring process at the proximal end of the tibiatarsus, which is especially large in the Emu, was not included in the measurement. (1927-1934), Heinroth (1922) and, for the Ostrich only, by Newton ( 1893-l 896). Most of these weights were based on a small but unstated number of captive specimens, usually of uncertain sex, age and sometimes specific identity. Stresemann' s weight for the Emu, which exceeds that of the Ostrich, 160 Weights of ratites are given by Stresemann THE CONDOR Vol. 49 Of the measurements discussed .above, the body length and the area of the femur are the only ones which, on the basis of the diagram and other considerations, seem to be correlated with weight. The proportions of the Cassowary appear most like those of July, 1947 WEIGHTS OF LARGEST BIRDS 163
doi:10.2307/1364110 fatcat:yksllxcanvdzbjfxx3dzn5gowm