Metabolism, Growth, and Activity in Adélie and Emperor Penguin Embryos

The eggs of Adelie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) penguins are smaller than those of large species in other orders. The incubation period in Adelie Penguins was as predicted based on egg mass, but in Emperor Penguins it was 50% longer than predicted. Although penguins have been described as semialtricial using the behavioral and morphological traits in Nice's (1962) classification, total oxygen consumption during incubation was similar to that of eggs of the same masses laid by precocial species. In both penguin species prepipping oxygen consumption was at a level predicted for precocial species. Adelie embryos grew continuously during the last two weeks of incubation, but the relative growth rate (%/day) of both wet and dry mass decreased steadily until day 32 of incubation. From day 21 to day 31 of incubation, there was no significant change in the wet mass, dry mass, or caloric content of yolk. The mass-specific caloric content of the embryos remained constant at 5.49 kcal/g dry mass. Activity of the embryo between pipping and hatching contributed importantly to measured oxygen consumption (10% of the total measured during incubation, -20% in pipped eggs from 3 days to 1 day before hatching, and -25% on the day of hatching). We suggest that the limited behavioral repertoire of hatchling penguins evolved as a response to the severity of the environment into which they hatch and because of the skilled predatory behavior that they must learn before they can feed themselves. Received 21 June 1985, accepted 6 January 1986. MANY investigators have measured the energy metabolism of avian embryos and discussed the empirical relationships between this and other functions, including embryonic growth, egg mass at laying, length of incubation, developmental type at hatching, adult mass, adult basal metabolic rate, and conductance of the eggshell (for recent reviews and discussions see C. Vleck et al. 1980, Rahn 1982, Bucher and Bartholomew 1984). A stated or an implicit assumption in most of these studies is that the contribution of activity to the total energy metabolism of avian embryos is minimal. Embryonic oxygen consumption usually has been measured in closed respirometry systems, except for very large eggs (D. Vleck et al. 1980) and in a few recent studies (e.g. Bartholomew and Goldstein 1984). Closed-system respirometry is integrative and gives only average values and rates of energy metabolism over relatively extended time periods. Recently, it has become possible to follow short-term fluctuations in energy metabolism by using flow-through respirometry and calculating instantaneous rates of oxygen consumption (Bartholomew et al. 1981). Continuous monitoring of rates of oxygen consumption of avian embryos over extended periods of time allows one to determine short-term variability in oxygen consumption of an individual due to activity as well as variation due to longer-term ontogenetic change. All members of the order Sphenisciformes are considered to be semialtricial (Nice 1962). Most lay their eggs in relatively to extremely cold environments characterized by low absolute humidity. Emperor (Aptenodytes forsteri) and Adelie (Pygoscelis adeliae) penguins breed on the Antarctic continent and its fringe islands and have a circumpolar distribution. There were no published data on embryonic growth and metabolism in penguins, so it was necessary to establish as broad a data base as possible from the combination of materials available to us (see Methods). We collected Adelie Penguin eggs of known age from colonies near Arctowski Station and Palmer Station in the Antarctic. We made physiological measurements on the eggs of Emperor Penguins and on the eggs and chicks of Adelie 485 The Auk 103: 485-493. July 1986 This content downloaded from 157.55.39.132 on Thu, 15 Sep 2016 06:17:50 UTC All use subject to http://about.jstor.org/terms 486 BUCHER ET AL. [Auk, Vol. 103 Penguins at Sea World in San Diego, California. Measurements of embryonic mass and accompanying yolk mass were obtained when possible to allow analysis of growth patterns and of energy allocation at specific times during incubation.