BAKKEN, G.S.*; WILLIAMS, J.B.: Effect of Wind and Growth on the Thermoregulatory Metabolism of Arctic-breeding Shorebird Chicks
Many Arctic-breeding shorebird chicks leave the nest and forage with one or both parents soon after hatching. Chicks may be exposed to temperatures near 0oC, and tundra habitats offer little shelter from wind. Parental attentiveness prevents severe hypothermia, but foraging time may be limited by thermoregulatory competence. We used open-circuit respirometry to measure the oxygen consumption and evaporative water loss rates of downy chicks of 3 species of Arctic-breeding shorebirds, the least sandpiper, (Calidris minutilla), short-billed dowitcher (Limnodromus griseus), and whimbrel (Numenius phaeopus). Chicks ranged from 9 to 107g in mass and were generally 85 to 350 hours old during measurements. Measurements were made at wind speeds of 0.1, 0.8, 1.8 and 3.0 m/s. Air temperatures ranged from 15 to 30oC, depending on age and species, and were selected so that standard operative temperatures always fell somewhat below the lower critical temperature. While chicks can withstand temperatures below 10oC for short periods with no wind, they frequently became hypothermic during extended (2 hour) measurements below 20oC with wind. Normothermic body temperatures during measurements averaged 39 �1oC for dowitchers and whimbrels. Sandpiper body temperature increased with age from 37 oC at 170 hours to 39 oC at 220 hours. As wind u increased from 0.1 to 3 m/s, mass-specific thermal conductance, K (W/g-oC) increased 62% for sandpipers, 42% for dowitchers, and 35% for whimbrels. The combined effects of mass and wind are approximated by log(K) = -2.1 -0.54 log(m) + 0.055u.
