Managing Wetland Vegetation for Marsh Birds and Waterfowl
 

Matt Bowyer and Tom Nelson

Department of Biological Sciences, Eastern Illinois University

BACKGROUND

Wildlife populations have benefited greatly from federal and state programs to acquire, protect and manage wetlands. But the high cost of developing wetlands, warrants careful assessment of the management potential of these areas. Successful management requires specific information on the influence of flooding and drainage on the growth and development of wetland vegetation. This study was designed to provide this information for restored wetlands in central Illinois.

OBJECTIVES

Our objectives were to identify plant species present in the seed bank of wetland soils, investigate the growth of these species in relation to the timing of summer drainage and quantify the abundance of waterfowl and marsh birds using these wetlands during migration and the breeding season.

STUDY AREA

The study was conducted on Carlyle Lake Wildlife Management Area near Vandalia, Illinois. The area consisted of four moist-soil units (MSUs) divided by levees (Figures 1 and 2). Each unit could be flooded or drained by water control structures and ditches. Prior to the development of these units, this land had been agriculture fields for over fifty years.

Figures 1 and 2. Four restored wetland units separated by levees at Carlyle Lake.

METHODS

We surveyed seed banks by collecting twenty soil cores in each MSU. Cores were transferred to the Eastern Illinois University greenhouse (Figure 4). Seedlings were identified and counted as they germinated. The number of seedlings growing in each core was converted to density per square meter for analysis. To investigate the influence of the timing of drawdowns on the growth of wetland vegetation, we drained two of the MSUs in early May and two in late June. The timing of drawdowns was reversed in these units during the second year of the study. We surveyed the vegetation growing in each unit during August of each year. Vegetation was sampled in 0.25-m² plots established along the transects where soil cores had been collected. Plants in each plot were identified and categorized into cover classes. MSUs were flooded again in October after the growing season and before the onset of waterfowl migration. We conducted weekly censuses from October-January to determine the species composition and abundance of birds using MSUs during the fall migration and winter. Weekly censuses were conducted from March-July to quantify use during spring migration and the nesting season.

Figure 4. Germinating seeds in the greenhouse

RESULTS

Viable seeds from twenty-three species of wetland plants were identified in the seed banks of the four MSUs. Seed densities were high in each unit, averaging 15,000 seeds/m² and species composition differed little among units (Table 1).

Table 1. Viable seeds/m2 in seed banks of wetland units.

Early drawdowns favored beggar-ticks, rice cut-grass and smartweeds.  Water hemp, water primrose and sedges grew best with late drawdowns (Table 2). Wildlife food plants were more common in early drawdowns.

Table 2. Percent cover of emergent vegetation in MSUs drained in May vs. June.

Early drawdowns were used heavily by birds during fall migration, particularly dabbling ducks. These MSUs held 75% of all birds in the fall (Table 3). However, late drawdowns were more heavily used during spring migration, perhaps because seeds had been depleted in early drawdowns during the fall and winter. Late draw-downs also provided important nesting habitat for marsh birds during the summer.

Table 3. Avian use of MSUs during fall migration.

MANAGEMENT RECOMMENDATIONS

Restored wetlands should be managed as marsh complexes with both early and late drawdowns to best meet the annual habitat requirements of waterfowl and marsh birds.

ACKNOWLEDGEMENTS

Funding for this research was provided by the Illinois Department of Natural Resources and Eastern Illinois University.