Long-term habitat degradation affects nest site selection behaviour by a freshwater turtle (Chelodina oblonga) in Western Australia

Freshwater turtles are one of the most endangered vertebrate groups with >60% of species threatened globally. Terrestrial nesting habitat degradation is a major threat to freshwater turtles, but the characteristics of nesting habitat remain poorly understood. This study investigated the nest site selection of the southwestern snake-necked turtle (Chelodina oblonga) to improve the conservation prospects for this species in an urbanized wetland area. In total, 235 depredated and 86 non-depredated nest sites and 320 non-nest locations were surveyed at Bibra Lake, Western Australia, during the Austral spring-summer, 2018-2023. A suite of environmental variables was measured at nest sites and non-nest locations. Analysis of similarities was used to determine whether nest sites and non-nest locations differed in their environmental characteristics. Generalized linear mixed models were used to identify environmental variables that best explained the nesting preferences. The environmental characteristics of nest sites differed from those of non-nest locations, with turtles nesting mainly in remnant natural habitat with greater canopy cover. Turtles generally avoided nesting in modified environments such as lawns and impervious surfaces. Factors influencing nest site selection are probably associated with the conditions necessary for regulating incubation temperatures and ease of nest excavation. This study suggests that modification of terrestrial vegetation around wetlands is adversely affecting freshwater turtle recruitment by removing or altering preferred nesting habitat. Protection and restoration of natural habitats fringing urban wetlands is important for the conservation of remnant freshwater turtle populations, and local partnership projects can help to achieve this.