EFFECTS OF PREDATOR REMOVAL ON MALLARD DUCKLING SURVIVAL

Abstract

We experimentally evaluated the effect of predator removal on mallard (Anas platyrhynchos) duckling survival in south-central Saskatchewan, Canada, in 2000 and 2001. Previous predator-removal research has focused on nest success, but our study was the first to document an effect on duckling survival. We compared 4 control sites (no predator removal) with 4 treatment sites where professional trappers removed common nest predators. Survival of 686 ducklings from 78 broods was determined using radiotelemetry and periodic counts of ducklings. Duckling survival was higher on predator-removal sites relative to control sites in 2000 and 2001 and negatively correlated with hatch date in 2000. Results of analyses including and excluding hatch date as a covariate suggest that hatch date was confounded with predator removal (i.e., predator removal influenced hatch dates). Based on these results, we concluded that duckling survival was affected by predator removal in 2 ways. First, predator removal increased duckling survival by removing predators that likely caused total brood loss. Second, in-the-year hatch date was negatively correlated with duckling survival, earlier average hatch dates on predator-removal areas contributed to increased duckling survival. Combining the 2 effects and averaging over years, 30-day duckling survival was 0.573 (90% CI: 0.492 to 0.657) on predator-removal sites and 0.357 (90% CI: 0.275 to 0.456) on control sites. We concluded that predator-removal efforts conducted primarily to increase nest success of upland-nesting ducks also increased survival of mallard ducklings.