Spatial distribution and population dynamics of free-roaming (stray and semi-domiciled) dogs in a major Brazilian city.

Introduction: Although estimate models have been proposed to determine free-roaming (both stray and semi-domiciled) dog populations, to date, no study has focused on the three major border areas of Brazil. Therefore, the present study assessed the free-roaming dog population of Foz do Iguaçu, a major far-west Brazilian city located in a three-border area (Brazil, Argentina, and Paraguay), which is considered among the top five Brazilian tourist destinations.

Methods: Capture-release sampling was performed in three phases with a 6-month interval and 10-day duration of each phase, totaling 18 months, between 2018 and 2019.

Results: A total of 1,273 dogs were estimated in the first [95% confidence interval (CI), 468-2,078 dogs], 904 in the second (95%CI, 452-1,355 dogs), and 1,564 in the third (95%CI, 521-2,607 dogs) capture phases in this area, suggesting a population density of 18.4 dogs/km (6.1-30.6 dogs/km, 95% CI). Of all free-roaming dogs, 452/1,125 (40.2%) were stray with no confirmed ownership or household, whereas 672/1,125 (59.8%) had a known origin, among which 625/1,125 (55.6%) were semi-domiciled with ownership or a household, 36/1,125 (3.2%) were neighborhood dogs with maintainers, and 11/1,125 (1.0%) were owned by recycling material collectors and homeless individuals. The majority of the 1,125 dogs (862/1,125; 76.6%) had an ideal body condition score. The high outdoor access of owned dogs is likely caused by cultural behavior. However, because 533/1,125 (47.4%) of the free-roaming dogs presented with clinical abnormalities, irresponsible ownership may have negatively impacted dog health and welfare.

Discussion: This study was the first to establish the density of free-roaming dogs, the ratio of stray and semi-domiciled dogs, and their dynamics over time in Foz do Iguaçu. The findings may serve as a warning for the high level of dog outdoor access and irresponsible guardianship, which may negatively affect animal health and welfare, leading to diseases, accidents, trauma, and animal cruelty.