Mortality and refuge use by young ring-necked ducks before and during hunting season in north-central Minnesota

Abstract

North-central Minnesota has a system of waterfowl refuges that were created over the last 6 decades to benefit ring-necked ducks (Aythya collaris). New refuges were placed to complement existing refuges and to relieve high hunting pressure in bog areas that were traditionally remote and inaccessible but were receiving increasing use. These refuges have been credited with keeping waterfowl in the area, but this has not been substantiated with data. Furthermore, the survival benefits of these refuges, if any, to locally produced ring-necked ducks have not been evaluated. We examined weekly mortality and movements onto and off of refuges with data from young ring-necked ducks captured and radio-marked before fledging. We used a multi-state model to investigate factors affecting transitions between 4 states (i.e., alive and on a refuge, alive and off a refuge, dead and off a refuge, and dead and on a refuge), and to account for variation in detection probabilities. Our most-supported model based on Akaike's Information Criterion with a small sample size correction (AICc) included movements onto and off of refuge as a function of year and hunting season, and mortality as a function of year, hunting season, and sex. The second ranked model (ΔAICc = 2.74) was similar to the top model but without the sex effect. Other models received considerably less support. Mortality was greater during hunting season than before hunting opened. Young males had greater mortality rates (mean ± SE) off the refuge than young females both before (0.050 ± 0.004 vs. 0.030 ± 0.002) and during hunting season (0.234 ± 0.019 vs. 0.137 ± 0.011). Probabilities of movement onto refuges were greater during hunting seasons than during weeks with no hunting pressure (0.073 ± 0.046 vs. 0.023 ± 0.015), although birds left refuges at a similar rate during hunting and before hunting seasons (0.424 ± 0.116 vs. 0.457 ± 0.125). Birds that used refuges were detected on the study area longer. Our findings are consistent with the hypothesis that ducks benefit from refuges; we found lesser mortality of birds on refuges (no birds were detected dead on a refuge), and greater mortality off refuges during hunting season. We did not evaluate whether survival benefits of refuges accrued from reduced disturbance, greater time foraging, benefits of membership in a flock, or simply safety from hunters. Future studies examining food availability and foraging behavior on and off refuges may help clarify the contributions of these variables to reducing mortality of young ring-necked ducks during hunting seasons. © 2013 The Wildlife Society.