Mallard survival, movements, and habitat use during autumn in Illinois

The Illinois River Valley (IRV) in central Illinois, USA, provides migratory stopover habitat for millions of waterfowl during autumn and spring in the Mississippi Flyway. Mallards (Anas platyrhynchos) are the most abundant species of waterfowl during autumn migration and the most harvested duck in Illinois. We investigated mallard migration ecology in central Illinois, USA, to address information needs of biologists and managers in the Upper Mississippi River and Great Lake Region Joint Venture and Illinois Department of Natural Resources. Our objectives were to document daily movements and identify factors affecting inter-wetland movements, investigate lengths of foraging flights, assess home range size during stopover, describe habitat use and identify factors associated with wetland use, estimate survival and cause specific mortality, and evaluate proportional use of refuges and areas open to hunting in and nearby the IRV by mallards. We employed standard radio-telemetry techniques to achieve our objectives during autumns and early winters 2009 and 2010 (n = 86 F and 56 M mallards). The mean movement distance between locations collected on consecutive days was 2,822 ± 120 (SE) m (n = 1,862; max. = 56,966 m) across age, sex, and months. Female mallards (n = 35) traveled 2,708 ± 191 m during evening foraging flights (n = 145) to agricultural fields and emergent marshes. Mean home range size (95% minimum convex polygon) was 21,306 ± 1,925 ha across sex and age classes (n = 81 mallards). We documented 43 mortalities of 142 radio-marked mallards (2009: 28.2%; 2010: 32.3%) with 85.0% and 69.6% of deaths attributed to hunting in 2009 and 2010, respectively. Body condition, hunting period, age, year, minimum daily temperature, and daily movement distance were important variables affecting survival, but differences were most pronounced for year and hunting period. Overall survival was greater in 2010 (Ŝi = 0.62) than 2009 (Ŝi = 0.39) and daily survival rates were 0.8% and 0.4% greater during closed than open hunting periods in 2009 and 2010, respectively. Mallards used open water most frequently across years (49.4% daily locations), followed by corn (dryland, flooded, standing, or harvested; 16.3%), herbaceous (10.6%), woody (10.5%), and other wetlands and upland cover types. Use of areas closed to hunting was low (18.7%) and most diurnal locations of mallards occurred in wetlands open to hunting (81.3%; i.e., not designated as refuge by statute). Similar to diurnal habitat use, female mallards returning from evening foraging flights (n = 138) used areas open to hunting (81.9%) more than refuges (18.1%). Refuges that were primarily composed of open water received low use by autumn-migrating mallards in the IRV. Restoration or rehabilitation of moist-soil and emergent wetlands within statutory refuges protected from unnatural flood regimes may improve foraging habitat quality and increase survival for mallards and other ducks during migration. © 2017 The Wildlife Society.