AUTHORS: Emily Buege Donovan, Southern Illinois University; Stephen Blake, Charles Darwin Foundation, Saint Louis University, Max Planck institute of Animal Behavior; Sharon L. Deem, Charles Darwin Foundation, Saint Louis Zoo; Ainoa Nieto-Claudin, Charles Darwin Foundation, Saint Louis Zoo; Patrick Moldowan, Charles Darwin Foundation; Freddy Cabrera, Charles Darwin Foundation; Cristian Peñafiel, Charles Darwin Foundation; Guillaume Bastille Rousseau, Southern Illinois University
ABSTRACT: Chelonians are among the most rapidly declining vertebrate groups due to habitat destruction and overexploitation by humans. Information pertaining to when, where, and how often tortoises nest and how nesting behavior responds to environmental variation is useful in developing conservation or remediation plans. However, direct observation of nesting behavior in wild populations can be logistically difficult. We sought to address knowledge gaps in the temporal and spatial patterns of nesting by Galapagos giant tortoises using GPS and triaxial accelerometer data. We applied a Random Forest classification algorithm to historical data from 54 individual Galapagos tortoises across four species from three islands. The algorithm categorized activity as either nesting or non-nesting, ultimately identifying approximately 150 nests between 2010 and 2023. Together with additional field-validated nesting behavior, our total data set consisted of over 250 nesting events. A minimum of 40 individuals nested in multiple years, allowing for year-over-year comparisons in reproductive phenology. We found variation in the timing of nesting both between and within species. In examining spatial patterns, we found that some individuals are highly philopatric, while others displayed more variation in nest site selection. These data provide insights into variation of nesting behavior in vulnerable and critically endangered Galapagos tortoises which can inform conservation strategies and management efforts to protect nests from invasive predators and consider mitigation strategies under climate change. Our approach could also help in addressing these and other conservation challenges in other systems with broad global relevance for threatened chelonians.
