Some Morphological Features of Avian Kidneys

Osc^a W. JOaNSON KNOWLEDCE of the external characteristics and weight of avian kidneys is fragmentary.Aside from generalized treatments (Stresemann, 1927-34; Benoit, 1950; Sperber, 1960), only limited information is available on external morphology (Kuroda, 1963 ) and kidney weight (Riboisiere, 1910; Crile and Quiring, 1940; Rensch, 1948; Quiring, 1962).Thus it seems appropriate to present the following data obtained as an adjunct to histological studies of the bird kidney.METI-IODS Preserved materials and other data were obtained from representatives of 181 species from 20 orders.I collected most of these birds myself in various portions of the United States, primarily in Arizona, Colorado, Minnesota, and North Dakota.The specimens were weighed (to 0.1 g) in the field, and the synsacra (kidneys in situ) were fixed in AFA or formalin.Later in the laboratory, the kidneys were dissected free, weighed (to .001g) in a sealed vial, and assigned to one of five categories (to be described later) representative of variations in external configuration.Prior to weighing, the kidneys were blotted lightly with absorbent paper.As used herein, kidney weight refers to the total of both organs in each individual.Where more than one specimen from a given species was available, mean kidney and body weight values were calculated.Additional body and kidney weight data from the literature (Riboisiere, 1910; Crile and Quiring, 1940; Quiring, 1962) were added to the above information.The supplement included 175 species not represented in my collection, and 14 species that were.The overlapping data were considered separately when developing the curve (Figure 1).In all 356 species from 23 orders are represented in the study.RESULTS AND DISCUSSION Weight.--Thedata are summarized in Table 1 and plotted logarithmically in Figure 1.The latter shows values ranging from hummingbirds to the ostrich (Struthio camelus).The data indicate a slight inverse relationship between kidney and body weight similar to those reported by Riboisiere (1910) and Rensch (1948).For the most part, the kidneys of relatively small birds (less than 100 g) exceed one per cent of body weight (latter level indicated by solid line in Figure 1).From 10.0 to about 1,000 g body weight, kidney weights are fairly evenly distributed around the one per cent line.In birds weighing more than 1,000 g, most kidney weights plot below the line.Because smaller birds metabolize more actively per unit body weight than do larger forms (King and Farner, 1961), the inverse kidney-body weight relationship probably reflects relative excretory demands.