Ecophysical Limits to Northern Breeding Distributions of Arctic Sandpipers

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9423522 Ricklefs The environment of the high arctic imposes two critical limits to the existence of many forms of life. One includes the extreme physical conditions of the environment: cold temperatures, high wind velocities, and low precipitation. The other is the briefness of the growing season. This environment is especially stringent for sandpipers (Scolopacidae), which occupy their arctic breeding grounds for as little as two months, and whose chicks are among the smallest of warm-blooded animals. This research project will utilize detailed measurements of the growth and development, energetics, thermal environment, food supply, and parental care of scolopacid chicks to discover how these birds exploit the arctic environment so successfully. Cold temperatures require a high capacity for generating metabolic heat; short breeding seasons require rapid growth. Therefore, the combined stresses of low temperature and short season would seem to push small homeotherms to the limit in the high arctic. The problem of resolving compromises between the conflicting functions of growth rate and heat generation is an excellent model for understanding how the design of the organism relates to its environmental setting. Field and laboratory measurements will be used to determine the forms of relationships and quantify the coefficients in a mathematical model of the scolopacid chick. The essential elements of the model encompass the internal organization of the chick and the relationship of the chick to its environment. The model changes continuously as the chick grows, and growth is simulated by expressions relating growth rate to functional capacity of tissues and functional capacity to the proportion of adult size achieved. Laboratory and field work will provide data to evaluate the scolopacid chick model. Laboratory investigation will focus on components of energy budgets, capacity of chicks to generate heat in response to cold stress, loss of heat from the b ody, including that caused by evaporation from the respiratory surfaces, and tolerance of body cooling. Observations of free-ranging chicks in natural family groups, using radio-tagged individuals where practical, will help to validate the results from penned birds. Conditions of the thermal environment and the availability of food items will be monitored continuously to provide data on the range and temporal variability of these factors.