NUTRITIONAL NEEDS FOR EGG FORMATION IN THE SHAG PHALACROCORAX-ARISTOTELIS

Egg production does not impose a major food need in the Shag Phalacroc orax aristotelis because the eggs are small, are formed slowly and are laid at 3-day intervals, I used dye-dosing of females, laying time an d, after fixing and staining the yolk, daily ring counts to estimate t he amounts of protein and energy needed each day to produce a clutch o f three eggs. Maximum daily nutrient needs during egg formation were o nly 1.15 g per day additional protein and 34 kJ per day energy, Yolk f ormation times of 40 eggs were 13.5 (+/-1.2 s.d.) days. Based on yolk- ring counts and laying dates of 15 eggs that contained dye, the lag pe riod between yolk completion and laying was 3.1 +/- 0.06 days. The dis tinct light and dark rings of the stained yolk resulted from differenc es in the transparency of the yolk spheres. In the dark rings, the sph eres were relatively clear, so more depth of stained yolk could be see n than in the light rings, which reflected the incident light.