Is the invasive pond slider (Trachemys scripta) favoured by a longer activity period than the native Mediterranean pond turtle (Mauremys leprosa)?

The annual activity patterns of the non-native pond slider (Trachemys scripta) and the native Mediterranean pond turtle (Mauremys leprosa) were assessed through transect surveys conducted in two irrigation channels in the Llobregat Delta (Barcelona, Spain), between July 2011 and May 2014. Individuals of T. scripta were categorised into four size classes (neonates, juveniles, subadults, and adults), whereas M. leprosa was treated as a single class including subadults and adults, as only two neonates and three juveniles were recorded. A total of 62 valid transects yielded 2525 T. scripta and 119 M. leprosa encounters. Activity of T. scripta began earlier in the season, with smaller individuals appearing in March and adults becoming more prominent approximately one month later, remaining active until October–November. A reduction in activity was noted during summer, particularly among adults and, to a lesser extent, subadults. Adult T. scripta ceased activity earlier than subadults and juveniles, which remained active until November. In contrast, M. leprosa was active from April to September, with reduced activity in October. Neonates of T. scripta were present in aquatic habitats from March to October, occasionally extending into November, with peak abundance in June. The longer annual activity period of T. scripta may confer competitive advantages in resource acquisition during more prolonged warm seasons, potentially contributing to its invasive success in Mediterranean wetland ecosystems. In addition, these results suggest an extended reproductive season with the potential for multiple oviposition events annually.