<p>While it is understood that an elevation in an ectotherm’s body temperature will bring about an increased metabolic rate (MR), the specific, quantitative increase in MR with temperature (e.g., the thermal metabolic sensitivity) varies among species. Thermal metabolic relationships for hatchlings of the estuarine, northern diamondback terrapin (<i>Malaclemys terrapin terrapin</i>), have not previously been quantified, leaving a data gap with respect to this species’ bioenergetics in the warmer, future climate. Hatchling diamondback terrapins derived from 18 nests in the field were assayed for routine metabolic rate (as O₂ consumption) at eight temperatures from 20.2 to 32.7&#xa0;°C following a 24-h acclimatization period. There was a positive linear relationship between Log₁₀ MR (per capita and per gram) and assay temperature. There were three apparent regions of thermal independence within the tested range, giving an almost stepwise pattern in MR in relation to increasing temperature. The temperature coefficients (Q₁₀) calculated across the range in assay temperatures showed that MR more than doubled over a 10&#xa0;°C range, with Q_{10 20.2–32.7} = 2.35 and 2.11 for per capita and per gram rates, respectively. In the absence of adaptation or perfect acclimation, an elevation in MR should alter the energy budget, requiring greater resource acquisition or reduced activity. Greater attention should be given to the physiological and subsequent autecological responses by ectotherms to contemporary and projected climatic conditions, as species-specific variation in the magnitude of the response will likely influence the nature and strength of competitive and predatory relationships.</p>