International Journal of Contemporary Research In Multidisciplinary, 2026;5(1):58-63
Cloacal Protuberance and Body Mass in Indian Passerine Birds: Comparative Study of Quantitative Relations
Author Name: Pawan Kumar; Manju Bhaskar; Rajni Singh; S.K. Bhardwaj; Suman Tanwar;
Abstract
Many passerine species exhibit seasonal reproductive cycles, with activity restricted to a narrow vernal window. During the onset of the breeding season, male gonads undergo physiological maturation to initiate spermatogenesis. The sequestration of sperm within storage reserves induces a physical distension of the cloaca, resulting in the formation of the cloacal protuberance (CP). The objective of this study was to test the quantitative relations of these two measures and to compare their vernal temporal changes. Relative size of the cloacal protuberance (cp) was scored, providing a cloacal protuberance index (CPI: 0 to + + + +) and body mass were measured by Electric balance (with accuracy +_ 0.005Gm). The breeding phenology varies significantly between pairs in some passerines. Consequently, it is often difficult to determine an individual male's reproductive status—specifically whether he is actively producing sperm—at the time of capture. In this study of captive birds, we demonstrate that cloacal protuberance (CP) volume is significantly greater in males during their reproductively active state compared to their own inactive state. Measurements of CP volume and body mass at a single time point, therefore, directly allow the researcher to reliably determine an individual's reproductive status.
Keywords
Spermatogenesis, Cloacal; Body mass (BM), Cloacal Protuberance index CPI, Reproductive Cycle and Breeding Phenology.