The Timing and Energetic Consequences of Egg Formation in The Adélie Penguin

-To study the timing of egg formation in the Adelie Penguin (Pygoscelis adeliue), we gave 150 females an oral dose of Sudan black dye before they laid their eggs. This lipophilic dye is incorporated into yolk synthesized on the day of dosing and deposited on the developing ovum as a blue layer. First, second, and third fresh eggs laid by dosed birds were collected. Analysis of the timing of egg formation revealed that rapid yolk deposition (RYD) on the first ovum began 10-l 2 days prior to cessation of feeding. Second and third yolks were initiated sequentially at 3-day intervals. The total time necessary for RYD was 14-17 days, and was followed by a 5to 7-day lag period between yolk completion and laying. In total, 19-24 days were required to produce each egg. Within clutches, second and third eggs were smaller than the first egg, owing to reduced albumen content, while yolk mass remained relatively constant. We determined the daily energy, protein, and lipid input into a clutch and estimated that the use of a female’s body reserves during a 12-day fast requires 307 g of muscle tissue. Of this, approximately 123 g of muscle (40%) are required to produce the 24 g of protein contained in egg components deposited during the fast. Both the long lag period and the 3-day interval between laying eggs may be adaptive in reducing the daily protein demand for egg production. The cost of egg production in wild birds has been the subject of considerable attention (see Ring 1973, Ricklefs 1974, and Murton and Westwood 1977, for reviews), but the importance of nutrient requirements for egg formation in such species has remained elusive and poorly understood. Egg formation in domestic hens, selected for rapid egg formation and prolonged productivity, cannot represent the avian model for this function, particularly when considering the temporal and energetic constraints attendant on most wild species. Our recent research (Grau ‘1984; Astheimer, in press) indicates that the process of egg formation is not evolutionarily static; there appear to be many species-specific variations which involve modifications both in the timing of formative events and in the rates of material deposition, either within the follicle or in the oviduct. Such differences would naturally affect any energy assessment of the daily production cost of a clutch. We chose to investigate the timing of egg formation in the AdClie Penguin (Pygoscelis adekze) to clarify the dynamics of egg production in a seabird that lays a two-egg clutch. We had previously concentrated on Cassin’s Auklet (Ptychoramphus aleuticus), which provided a simple model for egg formation of a single-egg clutch (Astheimer et al. 1980). An attempt to study this problem in eggs of the Fiordland Crested Penguin (Eudyptes pachyrhynchus) was limited to collection of single eggs of this species’ two-egg clutch owing to permit restrictions (Grau 1982). A preliminary study showed AdClie Penguins to be tractable experimental subjects (Grau and Wilson 1980) and, moreover, their highly synchronized reproductive timetable was delineated by distinct breeding events that could be related to the timing of egg formation. AdClie Penguins nest colonially on exposed islands and peninsulas in antarctic waters. Spring arrival often requires that the penguins cross many kilometers of sea ice on foot. After a brief prelaying period, during which courtship and nest construction occur, the female normally lays a twoegg clutch with a 3-day interval between eggs. Following clutch completion, she departs the rookery, ending her twoto three-week fast. Our purposes here were to (1) determine the timing of egg formation, (2) relate timing to the sequence of breeding events before laying, (3) compare differences within clutches in timing and egg composition, and finally, (4) estimate the daily and total nutrient costs of egg production for a female Adelie Penguin.