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The American crocodile (Crocodylus acutus) is the most widely distributed New World crocodile. However, the species has experienced severe declines due to overexploitation. In South Florida, loss of nesting habitat, with coastal degradation from sea level rise and urban development has prompted American crocodiles to nest in novel habitats. Crocodile Lake National Wildlife Refuge (CLNWR) serves as an important nesting site for the South Florida population of American crocodiles and more recently nesting habitat has been supplemented to manage coastal erosion. The goal of this study was to investigate the internal nest biology of American crocodile nests laid in sediment nourished sand mounds on CLNWR. We monitored internal nest temperature and volumetric water content of five live and two control sand nests in 2021 (N = 73 eggs) and 2022 (N = 84 eggs). The metabolic heat generated by incubating eggs in internal nest temperatures ranged from 0.8°C to 2.0°C warmer and more stable than ambient temperatures and reflecting a seasonal pattern. Average clutch size was 31.4 ± 7.09 eggs and incubation period ranged from 78 to 114 days until hatching. These data provide the first insight into thermal regimes of nests laid in novel/supplemented nesting habitat as is the case for a significant proportion of nests in the South Florida population of American crocodiles. Here we provide an opportunity to evaluate the importance of creating artificial nesting habitat for American crocodiles where habitat degradation from climate change threatens species survival. [ABSTRACT FROM AUTHOR]

Variable temperatures within a nest cause asynchronous development within clutches of freshwater turtle embryos, yet synchronous hatching occurs and is thought to be an important survival strategy for hatchlings. Metabolic compensation and circadian rhythms in heart rates of embryonic turtles indicate the potential of communication between embryos in a nest. Heart rates were used to identify metabolic circadian rhythms in clutches of an Australian freshwater turtle ( Chelodina longicollis ) and determine whether embryos metabolically compensate and hatch synchronously when incubated in asynchronous environments. The effects of a group environment during incubation on egg development and incubation period were also investigated during the final 3 weeks of development. Chelodina longicollis hatch synchronously and metabolically compensate so that less advanced embryos catch up to more advanced clutch-mates. Heart rates of embryos remained stable from week 4–7 in asynchronous (M = 89 bpm) and synchronous (M = 92 bpm) groups and declined in the final 2 weeks of incubation (M = 72 and 77 bpm). Circadian rhythms were present throughout development and diel heart rates of embryos in asynchronous groups showed less deviation from the mean (M = − 0.5 bpm) than synchronous groups (M = − 4 bpm). Eggs incubated in groups had a significantly shorter incubation period than eggs incubated individually. Phenotypic traits including size, performance, and growth of all hatchlings were not affected. Egg position within a turtle nest is important for coordinating development throughout incubation and facilitating synchronous hatching. [ABSTRACT FROM AUTHOR]