ENVIRONMENTAL CUES INFLUENCING THE BREEDING BIOLOGY AND CIRCULATING LEVELS OF VARIOUS HORMONES AND TRIGLYCERIDES IN THE CAPE CORMORANT

1. 1. Phalacrocorax capensis shows a well-demarcated summer breeding season. During this season gonadal weights, plasma levels of testosterone and luteinizing hormone are at peak levels. 2. 2. Plasma levels of circulating triglycerides and weight of stomach contents are also at their highest level during summer but body weight and fat index decline progressively during the breeding season. 3. 3. Although sexual activity is uniformly high during the summer breeding season, sexual activity of males precedes that of the females and two distinct peaks of activity occur within the breeding season which appear to be associated with the abundance, condition and reproductive activity of the main food item, namely pilchards. 4. 4. An analysis of the various environmental cues responsible for controlling the breeding season of P. capensis has been attempted. © 1979.