Mortality rates of feral ferrets (Mustela furo) in New Zealand

Abstract

Life-table data from feral ferret populations in New Zealand were analysed to estimate their mortality rates, and to test for any additive effect of Mycobacterium bovis infection on observed mortality rates. The observed instantaneous mortality rate was best estimated by modelling mortality as a 2-phase step model with different rates for juveniles (μ₁ = 1.45 year^–1, 95% C.I. 1.2–1.7 year^–1) and adults (μ₂ = 0.55 year^–1, 95% C.I. 0.4–0.9 year^–1). This corresponds to a survival probability of 0.25 during the first year of life, rising to 0.55 year^–1 thereafter, and a life expectancy of 0.95 years. At a population level, no additional mortality due to M. bovis infection was observed, suggesting either that the rate of disease-induced mortality was negligible, or that it was compensatory with natural mortality.