The physiological ecology of bats and turtles was investigated. A Doppler-radar unit was developed to non-invasively record the ventilation rate of unhindered free-hanging microchiropteran bats. The technique was then used to examine the arrhythmic breathing pattern of torpid pipistrelle bats (Pipistrellus pipistrellus). At ambient temperatures ranging from -1 to 14 oC arrhythmic breathing was most marked at colder temperatures. Active breathing could only supply a small proportion of the total O2 uptake, suggesting that during apnea the glottis remained open allowing a significant diffusive influx of O2. Radars were used to monitor the winter activity of a captive colony of brown long-eared bats ( Plecotus auritus). During winter these bats were found to emerge from their hibernaculum with a high daily probability (0.4 to 0.9), and upon emergence they tended to feed first and then drink. A model was developed to predict the optimum clutch size of loggerhead sea turtles (Caretta caretta). Due to their high energy expenditure whilst on land, it was predicted that turtles should lay clutches that are as large as possible. Hence clutch size should be constrained by the egg carrying capacity of the individual, and so it was predicted that larger individuals should lay larger clutches. This was found in a population of loggerheads in Greece. Clutch volume was found to be independent of the inter-nesting interval between successive nests laid by the same individual, and was found to decrease as the nesting season progressed due to a reduction in egg size with successive clutches. Nest site selection by nesting loggerhead turtles was studied. Sand temperature was found to play no part in nest site selection. However, nests were not deposited at random, but tended to be laid away from the sea close to vegetation that backed the beach. This pattern of nest placement was found to maximise hatchling survival. The emergence pattern of hatchling loggerhead turtles was monitored using a portable radar. Most hatchlings emerged at night, and hatchlings came out of all nests on more than one night (maximum 11 nights). Evidence suggested that the rate of cooling of the deep sand (≥ 15cm) was a factor initiating emergence. When the sand cooled faster in the evening, the hatchlings emerged earlier. The remigration pattern of adult sea turtles to a nesting beach over several years showed that individuals varied in their tendency to return in subsequent years. Evidence supported the hypothesis that the lower tendency of turtles seen nesting less than twice to return in subsequent years was due to them nesting on other beaches. A single female turtle was tracked by satellite for 58 days during the nesting season. The transmitter was attached after the turtle had been observed nesting. The satellite data revealed that the turtle subsequently made only localised movements and nested 3 more times, although never returning to the original nesting beach. Finally a method was developed to rigorously quantify the probability of identifying a nesting event by a turtle by satellite tracking, using field data combined with prediction software to calculate the time of satellite overpasses.