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Freshwater turtles are one of the most threatened vertebrate groups. Climate change is a major threat to these species, with impacts affecting all life‐history stages. There is currently a limited understanding of how changes in climate may alter the environmental triggers for hatching and emergence from the nests of freshwater turtle hatchlings. This precludes making predictions about how climate change may impact freshwater turtle recruitment success. The southwestern snake‐necked turtle (Chelodina oblonga) is endemic to south‐western Australia, a global biodiversity hotspot that has undergone severe climatic drying. Recruitment failure is thought to be occurring in many populations of the species. However, there is little understanding as to how environmental change may be influencing recruitment. This study aimed to: (1) determine the incubation duration and hatching and hatchling emergence success of C. oblonga, (2) determine if the species exhibits hatching or emergence synchrony and/or delayed emergence and (3) quantify the effects of temperature and rainfall on hatchling emergence. Using this information, the study assesses how climatic drying and warming may be impacting C. oblonga's early life‐history. Between 2018 and 2020 nest sites were monitored around a large urban wetland with weekly assessments of egg and hatchling status. Incubation duration and hatching and hatchling emergence success were calculated, and generalized linear models were built to determine how temperature and/or rainfall predicted emergence. Hatchlings either emerged shortly after hatching or overwintered in the nest, and both hatching and emergence were asynchronous. Both emergence periods were positively associated with temperature and rainfall. This study reveals that incubation duration, hatching success, hatchling emergence and survival are all likely to be impacted by recent and projected climate change, and especially drying. Warming and drying are predicted for many temperate regions globally, and it is therefore important that their impacts on the early life history of freshwater turtles be better understood. [ABSTRACT FROM AUTHOR]

The value of assisted colonisation as a response to climate change can only be realised if focal species are well suited to their new habitats. For ectotherms, new habitats must offer microclimates that promote crucial behaviours such as thermoregulation and foraging.The Western swamp turtle Pseudemydura umbrina, a Critically Endangered species from south‐western Australia, serves as a global case‐study of assisted colonisation in action. Initial trials where juvenile P. umbrina were released into wetter and cooler climates found that individuals spent considerable time at body temperatures that apparently limited their growth.Using high‐resolution biologging data (temperature and depth), here we tested if turtle activity is thermally constrained in cooler latitudes by releasing 48 juveniles into seasonal swamps at three sites. One site was core natural habitat, and the other sites were wetlands 380 km apart that offered either warmer or cooler microclimates. Generalised additive mixed models were used to evaluate behaviours and time spent at optimal temperatures for approximately 1 month following release, and growth rates were measured and analysed after release until the end of the hydroperiod 4–5 months later.We found that turtles released into the most poleward (southern) wetland spent significantly less time active and basking and grew significantly less compared to turtles released further north. When analysed together, behavioural and growth datasets showed that activity was positively correlated with growth rates.We conclude that poor growth of turtles in the southern wetland was likely a result of lower body temperatures, stemming from a reduced ability to thermoregulate in water. Consequently, for assisted colonisation of juvenile P. umbrina to be successful, recipient wetlands must offer aquatic microclimates that are sufficiently warm to promote foraging activity that leads to growth, and ultimately to maturation. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]