Understanding within-patch seasonal demographics of patchily distributed odonates is fundamental to understanding aspects of their behaviour, ecology, and landscape-scale population dynamics. Such knowledge underpins effective conservation management and is dependent upon appropriate survey methods. The objective of this study was to understand the within-patch, flying season, population dynamics of imagos of the endangered mire-dwelling dragonfly, Petalura gigantea, using a modified Pollard Walk, a line transect survey technique. Relative abundance of imagos was monitored at nominally weekly intervals, by sex, across the duration of the flying season in six mire patches in the Blue Mountains, New South Wales. There was a preponderance of adult males and a relatively consistent trend in changing relative abundance of adult males compared to females within mire habitat across all surveys, with a marked seasonal peak in male abundance, confirming that surviving adult females generally occupy non-mire habitat other than for reproduction. This study confirmed the utility of this technique to monitor changing relative abundance of adult males within mire patches across a flying season, and potentially, for comparison among years for a separate, longitudinal, landscape-scale study. Successful use of the technique is contingent upon a sound understanding of the species’ habitat preferences and behaviour, with caveats for survey timing and weather protocols, to satisfy minimum requirements for detectability, repeatability, and replicability. The technique could be used, with species- and habitat-specific modifications, for monitoring other patchily distributed odonates, including petalurids, and contribute to their improved conservation management.