1. ABSTRACT Research on individual energy budgets has contributed greatly to our understanding of a wide range of ecological phenomena from life history evolution to ecological energetics. Modeling energy budgets of animals requires a detailed understanding of the physiological processes of energy assimilation during digestion, which includes estimating the cost of digestion. However, the standard method to measure the cost of digestion (by integrating the difference between digesting and standard metabolic rates over the time between feeding and defecation) assumes that the animals are resting or at least equally active while fed and fasted, which is not always true. Thus, activity metabolism can lead to inaccurate estimate of digestive costs. We have developed a novel method to measure the cost of digestion of the Eastern Fence Lizard (Sceloporus undulatus) that removes the effects of lizard activity during metabolic measurements. We used infrared time- lapse video imaging and a Sable Systems oxygen analyzer to simultaneously measure the rates of activity and metabolism. Using a Scalex Plan Wheel and our own device driver, we analyzed the videos to assess lizard movement rates during their metabolic rate measurements. Data indicate that even slight chamber activity (e.g. moving 1m/24 min) can significantly elevate metabolism. Our results over a range of temperatures show significant improvement in estimating the cost of digestion by removing the effects of activity metabolism.

2. Figure 3A - Lizards in temperature-controlled, double- walled glass tubes (metabolic chambers).

4. time (mins) position (cm) A B C Figure 8 - Representative lizard movement patterns for points marked A, B, and C from Figure 7.

5. metabolic rate (ml O 2 /h) total distance (cm) Figure 9 - Total distance vs. metabolic rate at 35 o C for: lizard R 2 A#9unfed0.77 B#9 fed0.68 C#5unfed0.67 D#5 fed0.44 E #4 fed0.53 AB D E C

6. total distance (cm) MR (ml O 2 /h) adjusted MR (ml O 2 /h) Table 1 - Sample calculations of “adjusted” metabolic rate removing the effects of elevated metabolism due to movement activity for the unfed trial of lizard #4. “Adjusted MR” = MR - 0.0252 * distance, where the number is the slope of the regression for the first 2 columns of data (see Figure 7).