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Marcus Webster


In this study I measured resting metabolic rate (RMR), costs of thermoregulation, and specific dynamic action (SDA) in House Finches and I tested the hypothesis that SDA heat substitutes for costs of thermoregulation at low temperatures in House Finches. Oxygen consumption of both bed and fasted birds was measured at three different temperatures (5 C, 15 C, and 30 C) using an open flow metabolism system and converted to metabolic rate (kJ/hr) using caloric equivalents. RMR, obtained from the fasted metabolic rate within the thermoneutral zone (30 C) was 1.65+.10 kJ/hr. Costs of thermoregulation at 15 C and 5 C were measured as the difference between fasted metabolic rate at these temperatures and the RMR. At 15 C costs of thermoregulation were .41 kJ/hr and at 5 C were .59 kJ/hr. SDA was calculated from the difference in the metabolic rates between fed and fasted birds and expressed as a percent of gross energy intake (GEI). SDA averaged 3-5% of GEI. No effect of temperature on SDA was observed. At 30 C SDA was 4.12% of GEI and at 5 C was 3.68% of GEI.SDA is expected to decease with decreasing temperature if it substitutes for the costs of thermoregulation at low temperatures. I found no evidence to support the substitution hypothesis. High variability, however, made it different to draw solid conclusions.

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