Assessment of sexual size dimorphism in Pilbara Olive Pythons (Liasis olivaceus barroni) and observations related to reproduction

The Pilbara Olive Python (Liasis olivaceus barroni) is a large-bodied python endemic to the Pilbara and northern Gascoyne regions of Western Australia. Despite its national listing as Vulnerable, data on its morphology, sexual size dimorphism, and reproductive ecology remain limited. We present data from a 4-year monitoring and radio-tracking program comparing measurements from 100 individuals sampled across 12 locations. Allometrically scaled morphometric analyses found minimal evidence of sexual size dimorphism, with males and females showing largely overlapping body proportions. Breakpoint analyses of body mass relative to snout–vent length indicated that males reach sexual maturity at smaller sizes (~1320 mm SVL) than females (~1805 mm SVL). Observations of reproductive activity showed a defined seasonal cycle, with females ovulating in September, gravid in October, and brooding in refuges between October and February. Juveniles were most frequently detected from November to February, with neonate-sized individuals detected in January. Both natural (caves, rocky outcrops, burrows) and artificial shelters (engineered rock wall) were used for brooding, highlighting flexibility in reproductive behaviour. These findings provide the first population-level assessment of sexual size dimorphism and reproductive timing in this subspecies and offer critical baseline data to inform conservation management.