Data Sheet 1_Beyond population size: long-term changes in free-roaming cat population structure during TNR implementation in Seoul.docx

A logistic mixed effects model assessed apparent retention by baseline neutering status, and within-year encounter histories were used to estimate detection probability.</p>Results<p>Overall population size and density showed a decreasing temporal pattern, while neutering rates generally increased and kitten proportions generally decreased. At the survey-year level, higher neutering rates coincided with lower kitten proportions.

After adjustment for covariates and site-level clustering, cats neutered at baseline had significantly higher odds of apparent retention than non-neutered cats (OR = 3.06, 95% CI: 2.07–4.53). The pooled single-visit detection probability was 0.299, indicating that apparent retention remained subject to imperfect detection. In exploratory site-level comparisons, sites maintaining high neutering rates showed patterns consistent with lower kitten proportions and higher apparent retention, whereas sites with declining neutering rates showed patterns consistent with greater apparent turnover and higher kitten proportions.</p>Conclusions<p>These findings describe population-structure patterns observed during implementation of Seoul's public TNR program, including reduced kitten counts and increased neutering probability over time.

Given the observational nature of the study and the absence of untreated controls, these findings cannot demonstrate the causal effects of TNR. Nevertheless, structural indicators may complement simple procedure counts to identify sites requiring further intervention in urban cat management.</p>