Geophagy is the consumption of hard objects with no caloric value (e.g. soil, sand, sediment) called gastroliths. This behaviour is widespread in animals, and among reptiles, geophagy has been reported in crocodilians and lizards and occasionally in chelonians. In this study, we calculated geophagy rates in snapping turtle (Chelydra serpentina) and painted turtle (Chrysemys picta) hatchlings under various incubation protocols, ranging from highly artificial to semi-natural conditions. Among multiple experiments where eggs were incubated atop the nesting substrate, 66% of painted turtle and 58–93% of snapping turtle hatchlings exhibited geophagy within 24 h of hatching. Snapping turtle hatchlings that experienced a simulated natural nest emergence had an 85–100% rate of gastrolith consumption. Hatchling snapping turtles from shallow simulated nests emerged earlier and had higher rates of geophagy compared with those from deeper nests. Given the high frequency, short time period (24~72 h) and variety of incubation protocols under which geophagy occurred, we suggest that this behaviour is intentional. We discuss multiple hypothesis for the adaptive and functional significance of geophagic behaviour with respect to chelonians, synthesize existing literature on chelonian geophagy and highlight the possible implications of hatchling turtle geophagy for ex situ captive breeding and head-starting programs. Given that hatchlings readily consume their incubation medium, caretakers should carefully consider the substrate their animals are exposed to. Future research should address how widespread geophagy is among hatchling turtles and the possible role of this behaviour for hatchling ecology and health, including effects on the gut microbiome. Animals regularly consume non-caloric foods, such as rocks and soils. This behaviour is exhibited by hatchling turtles, but why? Our literature review suggests that the ingestion of non-caloric foods by turtles is important for nutrition and, in particular, this behaviour may help establish gut health in hatchlings. Observational and experimental study demonstrated that nest characteristics in-part account for why hatchling ‘turtles eat dirt’. This has applications for hatchling ecology as well as captive rearing conservation programs, an increasingly common strategy for the conservation of these globally imperilled animals. This work complements several recent studies and review articles about geophagy in other major vertebrate groups (birds, mammals) and provides a comprehensive summary on the current state of knowledge of this behaviour for turtles.

中文翻译：

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幼龟以高频率摄取天然和人工孵化基质

Geophagy 是消耗没有热量值的坚硬物体（例如土壤、沙子、沉积物），称为胃石。这种行为在动物中很普遍，在爬行动物中，据报道鳄鱼和蜥蜴以及偶尔在龟类中发生食土。在这项研究中，我们计算了鳄龟 (Chelydra serpentina) 和锦龟 (Chrysemys picta) 幼龟在各种孵化方案（从高度人工到半自然条件下）的食土率。在将卵孵化在筑巢基质上的多个实验中，66% 的锦龟和 58-93% 的鳄龟幼龟在孵化后 24 小时内表现出食地行为。经历了模拟自然巢穴出现的鳄龟幼龟的胃石消耗率为 85-100%。与来自较深巢穴的幼龟相比，来自浅层模拟巢穴的鳄龟幼龟出现较早，并且具有更高的食土率。鉴于发生噬菌体的频率高、时间短（24~72 小时）和各种孵化方案，我们认为这种行为是有意为之。我们讨论了关于海龟食食行为的适应性和功能意义的多种假设，综合了关于海龟食食的现有文献，并强调了幼龟食食对易地圈养繁殖和启动计划的可能影响。鉴于幼龟很容易消耗其孵化介质，看护人应仔细考虑他们的动物接触的基质。未来的研究应该解决幼龟中的食地行为有多普遍，以及这种行为对幼龟生态和健康的可能作用，包括对肠道微生物群的影响。动物经常食用无热量的食物，例如岩石和土壤。幼龟会表现出这种行为，但为什么呢？我们的文献综述表明，海龟摄入无热量食物对营养很重要，特别是这种行为可能有助于建立幼龟的肠道健康。观察和实验研究表明，巢穴特征部分解释了为什么孵化的“海龟吃泥土”。这适用于孵化生态学以及圈养饲养保护计划，这是保护这些全球濒危动物的越来越普遍的策略。