Migrating and breeding bird use of restored shallow lakes in Iowa

Large shallow lakes in the Prairie Pothole Region (PPR) have become highly degraded since European settlement. The Shallow Lakes Restoration Program aims to restore Iowa’s shallow lakes to improve water quality and wildlife habitat. The goals of this study were to (1) assess the differences in migrant waterbird species composition, abundance, and diversity in shallow lakes in non-restored, younger, and older states and identify habitat variables that influence migrant waterbirds, (2) quantify the density of breeding marsh birds in shallow lakes in different restoration states, and (3) characterize the vegetation community among shallow lakes in different restoration states. Restored sites had a greater number and diversity of waterbirds during spring migration. Early in the season, older restorations had a greater abundance and species richness than younger restorations. Wetland area and water level change influenced the abundance of some waterbirds, while the abundance of several groups (e.g., diving ducks) showed a quadratic relationship with emergent vegetation. Older restorations had the greatest densities of breeding marsh birds. Observer bias, vegetation height (+, -) and density (-), time of day (+, -), and wind speed (-) influenced the detection of some species of breeding marsh birds. We also found that younger restorations had a greater number of emergent species than both non-restored sites and older restorations, but restored sites had the greatest diversity of emergent, floating-leaved, and submersed aquatic vegetation. Submersed aquatic species had a positive relationship with restoration age, but species sensitive to water quality were less abundant in older restorations than younger restorations. Marsh passerines and rails had a positive relationship with frequency of occurrence of aquatic vegetation and cattail (Typha sp.). These results emphasize the importance of restoration to migrating and breeding marsh birds, but further management action may be necessary to maximize the benefits of these wetlands to birds