Egg Weight Loss and Nest Humidity during Incubation in Two Alaskan Gulls

Abstract

Although weight loss of eggs during natural incubation has long been recognized, little is known about the mechanism by which water vapor is conveyed from the eggs to the atmosphere surrounding the nest. It has been suggested that this occurs in two steps: (1) molecular diffusion from the egg across the gas-filled pores of the shell to the microclimate of the nest, (2) convection from the microclimate of the nest to the ambient environment (Rahn et al. 1976, 1977). To evaluate these processes, one must not only measure the flux of water from the egg but also estimate or measure the vapor pressure of water in the egg, the nest and the ambient atmosphere. We attempted this in the Black-legged Kittiwake (Rissa tridactyla) and the Glaucous-winged Gull (Larus glaucescens) when they were nesting on Gull Island, Kachemak Bay near Homer, Alaska, during June 1974. In this study we have determined the rate of water loss from the egg during natural incubation, the egg temperature, the water vapor conductance and physical dimensions of the egg, and calculated the water vapor pressure of the egg, the microclimate of the nest and the nest ventilation.