A fragmental observation on avian kidney

Abstract

The external morphology of avian kidney was compared by examining 39 species of 17 Orders of birds. The kidney type was characteristic by Orders, but also differed among families adaptively according to the pelvis type which is adapted to a particular mode of life or food habit. In a few cases, the kidney type showed apparent taxonomic significance supporting the results otherwise reached (such as osteology).
Among the Passeres examined, starlings showed slight difference of kidney type from general one and the Sylviidae (Acrocephalus, Locustella) had definitely different narrow type as the result of laterally compressed pelvic girdle adapted to live in the thickets and reeds. Among Anseres, the resemblance showed by Bucephala and Mergellus and their intermediate type between Anas and Mergus are of interest in supporting general taxonomic opinion. The phylogenetic affinity between Sphenisci and Tubinares generally believed was also suggested from their kidney types. On the other hand, Fregata and Sula of the same Order, but entirely different in habit (thus different in pelvis type) had quite different type of kidney but Sula resembled Nannopterum, a cormorant, in their long type.
The kidney varied from very simple and possibly really primitive type, only with anterior and posterior (in kingfisher Ceryle almost no division) lobes to complicated and possibly advanced one with middle and lateral lobes, but several weighing results suggested that the kidney occupies more or less 1% of the body weight (fat excluded) probably similarly in large and smaller birds. But, it might be speculated (partly from the result of the present study) that sea birds may have relatively more voluminous kidney and the basic kidney function might supplement the function of salt glands.
In Cygnus the kidney was peculiar in being divided into numerous small lobes and the general size was not voluminous for the bird. Thus in large flying birds the kidney may split to pieces to augment the surface and not the volume thus keeping the body light. The division of anterior, middle, lateral and posterior lobes in general birds may also be the result of such an adaptive devise.