Free-roaming dogs in Ushuaia City, Tierra del Fuego, Argentina: How many and why

Abstract

Free-roaming dogs (FRD) in cities represent an increasing problem. Authorities need numbers of FRD to evaluate policies implemented and to monitor the dog population. We estimated the number of FRD in Ushuaia city, Argentina, using a photographic capture-recapture methodology. We estimated an abundance index, the power to detect changes in the index, and modeled factors that may explain the spatial distribution of FRD and their welfare status. We also infer whether if they are represented by partially supervised or unsupervised dogs, using a health and welfare index based on body fat coverage and skin condition, as well as on the presence of collars or accessories as a proxy of evidence for tenure. During three surveys, covering 72 transects along streets (9.9% of the street layout of Ushuaia), we recorded 539 different FRD. A model with individual heterogeneity in capture-recapture probability gave 12,797 FRD (95% CI 10,979—15,323), reflecting a dog:human relation of 1:6, higher than the relation recommended by the World Health Organization (WHO). The abundance index was similar between surveys (8.13 ± 1.36, 8.38 ± 1.46 and 9.55 ± 1.28 dogs/km). The difference needed to detect changes in the index is about twice the standard error of estimates. The best model explaining dogs’ abundance included only geographical location, although two neighbourhoods with 9 transects stand out with 181 different FRD identified. Together with the good overall dogs’ welfare status, modeling suggests that the behavior of owners is the main driver for the presence of FRD. We recommend the use of photographic capture-recapture methodologies instead of simple index estimation, due to the small additional effort required and the improved accuracy and precision obtained. We also recommend a permanent systematic design for future surveys, increase the number of survey occasions, and improve the survey process.