Population dynamics of free-roaming dogs in Europe and implications for population control

Abstract

Changes in free-roaming dog population size are important indicators of the effectiveness of dog population management. Assessing the effectiveness of different management methods also requires estimating the processes that change population size, such as the rates of recruitment into and removal from a population. This is one of the first studies to quantify the size, rates of recruitment and removal, and health and welfare status of free-roaming dog populations in Europe. We determined the size, dynamics, and health status of free-roaming dog populations in Pescara, Italy, and Lviv, Ukraine, over a 15-month study period. Both study populations had ongoing dog population management through catch-neuter-release and sheltering programmes. Average monthly apparent survival probability was 0.93 (95% CI 0.81-1.00) in Pescara and 0.93 (95% CI 0.84-0.99) in Lviv. An average of 7 dogs km-2 were observed in Pescara and 40 dogs km-2 in Lviv. Per capita entry probabilities varied between 0.09 and 0.20 in Pescara, and 0.12 and 0.42 in Lviv. In Lviv, detection probability was lower on weekdays (odds ratio: 0.74, 95% CI 0.53-0.96) and higher on market days (odds ratio: 2.58, 95% CI 1.28-4.14), and apparent survival probability was lower in males (odds ratio: 0.25, 95% CI 0.03-0.59). Few juveniles were observed in the study populations, indicating that recruitment may be occurring by movement between dog subpopulations (e.g. from local owned or neighbouring free-roaming dog populations), with important consequences for population control. This study provides important data for planning effective dog population management and for informing population and infectious disease modelling. The results emphasise the importance of dog population management efforts that encourage responsible ownership through reduced abandonment and cover the entire city to reduce the risk of dog movement between sections of the city hindering management efforts.