Historical and Contemporary Characteristics and Waterfowl Use of Illinois River Valley Wetlands

Understanding changes in characteristics of floodplain wetlands over time could provide valuable information to guide management and restoration efforts. We compared characteristics of 29 Illinois River valley (IRV) wetlands mapped during two time periods between 1938-1959 and 15 wetlands re-mapped in 2005-2006. Average proportions of wetlands classified as bottomland forest, scrub-shrub, nonpersistent emergent, and mud flat were generally greater during 2005-2006 than 1938-1942 or 1943-1959, but proportions of aquatic-bed and floating-leaved vegetation declined significantly by 2005-2006. We also modeled wetland use by mallards (Anas platyrhynchos) and diving ducks (Tribe Aythyini) during falls 1950-1959 in relation to wetland characteristics. Proportion of wetlands classified as nonpersistent emergent and an interspersion-juxtaposition index (IJI) positively associated with mallard use, whereas proportions of scrub-shrub and persistent emergent vegetation influenced diving duck use negatively. Use by both groups associated positively with wetland area and refuge. The loss of submersed and floating-leaved aquatic vegetation emphasizes the need to restore conditions that promote diverse plant communities in IRV wetlands. Composition and arrangement of wetland habitats (indicated by IJI) may be an important attractant to migrating mallards and perhaps a consideration when planning and evaluating wetland conservation efforts in mid-migration regions.