Introduction: The effective management of free-roaming cat populations depends on the robust monitoring of population size and welfare. This study compared two approaches, direct Mark–Resight patrol surveys and a virtual Mark–Resight method using camera traps, to evaluate a sterilized free-roaming cat population in a defined area.

Methods: Monitoring was conducted once every five weeks for one year. Each monitoring series included two consecutive days with surveys at sunrise and sunset (four observation events per series). In routine patrols, observers followed a standardized route at a fixed pace, recording encountered cats and identifying individuals using natural markings (coat pattern, scars, facial shape). In the camera trap method, two motion-activated cameras and an automatic feeder at a structured feeding station collected images via motion trigger and time-lapses. Images were reviewed post hoc to identify individuals. For each physical or photographic encounter, sex, age class (adult/young), sterilization status (indicated by surgical ear-tip removal), body condition score (BCS), and injury score were recorded. Population size was estimated per series using the Lincoln–Petersen Mark–Resight model, averaging morning and evening estimates.

Results: Routine patrols detected significantly more cats than camera traps throughout the study (32.5±1.6 vs. 15.8±0.09;P<0.0001). Both methods showed higher detection at sunset vs. sunrise (camera traps P=0.0119; patrols P=0.0002). Camera traps detected a higher proportion of young cats (P<0.0001) and showed a slightly better identification of sterilization status (P=0.0045). In patrols, young cats had lower BCS than adults (P=0.0058), with a similar trend in camera traps (P=0.0858). Variance in BCS and injury scores was greater in patrols (BCS: P=0.0163-0.0184; injuries:P=0.0517-0.0593), indicating superior sensitivity for welfare assessment.

Conclusions: Each method demonstrated distinct strengths: patrol surveys more accurately captured total population size and welfare indicators, while camera traps improved the detection of young cats and sterilization status. The combined use of both methods provides a more comprehensive framework for monitoring urban free-roaming cat populations.