The Role of Climate and Species Traits on the Timing of Spring Emergence in Amphibians and Reptiles

ABSTRACT Aim The timing of spring emergence from brumation is crucial for amphibians and reptiles, because it coincides with resource availability and the onset of the breeding season. Here, we investigated how climatic factors and species traits interact to affect the timing of spring emergence in amphibians and reptiles, and how species traits mediate predicted shifts of this important phenological process under future climate scenarios. Location Northern hemisphere. Time Period 2010–2100. Major Taxa Studied Amphibians and reptiles. Methods Using > 2.6 million citizen observations of 97 amphibian and 182 reptile species, we first show that citizen data can be used to estimate the onset of spring emergence and then use this dataset to quantify and predict how climate and species traits affect large‐scale patterns of emergence timing, using Bayesian phylogenetic mixed models. Results Mean annual temperature was the most important factor determining spring emergence, with species in warmer regions becoming active earlier, and amphibian and reptile emergence predicted to advance by approximately 25 and 17 days, respectively, under a 4.3°C warming scenario by 2100. Species traits related to reproduction and physiology further explained phenological variation, with explosive‐breeding anurans emerging earlier than prolonged breeders. Moreover, urodeles with direct development and viviparous reptile species emerged comparatively later, with this pattern mediated by temperature, being more pronounced in colder regions. Main Conclusions Combined, our results highlight key climatic and biological drivers relevant for predicting amphibian and reptile species responses to global climate change, which may help us anticipate phenological mismatches, assess vulnerability, and prioritize conservation efforts.