A decade of tracking reveals strong nest site fidelity in four Galapagos giant tortoise species

Flexibility of reproductive behavior and physiology in response to environmental cues may buffer populations against the impacts of rapid environmental change. These responses are especially critical for oviparous species, as reproductive outcomes are particularly sensitive to conditions during incubation. Behavioral plasticity in reproduction can be expressed through traits such as nest site selection and nesting phenology. However, the degree to which these parameters are flexible remains poorly understood for many chelonian species, including Galápagos giant tortoises Chelonoidis spp. We applied a previously developed machine learning algorithm to over a decade of GPS and tri‐axial accelerometry data to examine spatial and temporal nesting patterns in four threatened to endangered species of Galápagos tortoise, C. donfaustoi, C. hoodensis, C. porteri and C. vandenburghi, across three islands in the archipelago. We identified 391 nests from 50 females laid between 2010 and 2024. Females typically nested more than once per year (1–4 nests detected per year) and had high annual nesting rates (proportion of years in which a female nested, mean = 0.87). Individual females showed nest site fidelity within and across years by returning to specific areas to nest, often placing successive nests < 300 m apart. While nest dispersion varied substantially by individual and species, we detected no variation in nest dispersion across years or between female C. donfaustoi with migrant or resident movement strategies. However, we did detect significant differences in the timing of nesting across species. Understanding these patterns improves our knowledge of the reproductive ecology and flexibility of long‐lived reptiles. Generating novel insights into nesting phenology and nest placement from accelerometry will facilitate linking nesting behavior to environmental drivers of reproductive variation, reproductive outcomes, and conservation management in Galápagos tortoises and other threatened chelonians.