Blue geese at McConnell River, N.W.T., lost 20% of eggs, mostly late in incubation. Parasitic jaegers and herring gulls were attracted to the colony and were efficient at finding eggs although geese defended their nests strongly. Since egg loss could only occur in the absence of both geese, jaegers, and gulls acted as scavengers rather than predators. Factors causing desertion were the true causes of egg loss. These may have been inexperience of younger geese, or starvation during incubation.During nesting, geese had very little to eat and lost about 25% of spring weight. While the birds were fasting, weight loss is a function of heat loss, in turn controlled by weather conditions. The relationship between heat loss and several weather parameters was determined by means of a water-heated model goose in a simulated environment. This relationship allowed prediction of heat loss, and hence weight loss, from air temperature, wind speed, incident radiation, and goose surface temperature.Severe weather could result in considerable weight loss and it is suggested that this impaired the goose's ability to incubate steadily. Extreme weight loss could result in death, and many nesting geese were found apparently starved during the hatch.