Availabilty of Potential Invertebrate Foods for Anatini Ducklings Above and Below the Water Surface of Eastern South Dakota Wetlands

The availability of aquatic and aerial invertebrates as potential foods for Anatini (dabbler) ducklings was explored during the summers of 1998 and 1999 in eastern South Dakota. Two study areas, the Oakwood Lakes complex and Mickelson Memorial Wetland, were chosen for this research during the summer of 1998. In 1999, a third area, Redetzke Game Production Area (GPA), was added. Wetlands within the preselected study areas were classified as either high-use or low-use by dabbler (Anatini) duckling broods according to brood observations. Aquatic and aerial invertebrates were collected from these wetlands using funnel traps and sticky traps, respectively. Aquatic and aerial invertebrates were sorted and identified to family. Total and taxa abundance and volume displacement were measured. Additional habitat characteristics were also measured at each sampling site. Simple correlation revealed no similar trends in invertebrate abundance and volume during 1998 or 1999. In 1998, there was no apparent association between aquatic and surface invertebrate abundance (r=0.022, P=0.197) or volume (r=0.003, P=0.655). Similar results were found for aquatic and surface invertebrate abundance (r2=0. P=0.995) and volume (r=0.001, P=0.850) in 1999. Mean aquatic and aerial invertebrate abundance and volume were compared between wetlands receiving high- and low-use by ducklings. In 1998, aquatic invertebrate abundance was greater in high-use areas compared to low-use areas (P=0.027) while it was statistically similar between areas in 1999 (P=0.337). High- and low-use areas had similar aquatic invertebrate volume in 1998 (P=0.283). In contrast, 1999 low-use areas had greater aquatic invertebrate volume compared to high-use areas (P=0.069). Aerial insect abundance was greater in high-use areas compared to low-use areas in 1998 (P=0.097) whereas aerial insect abundance in 1999 was similar between areas (P=0. 337). Low-use areas had greater aerial insect volume than high-use areas in 1998 (P=0.038) while no differences were detected between surface insect volumes in 1999 high- and low-use areas (P=O. 126). Adult chironomids, a favorite food of many ducklings, were more abundant in high-use areas compared to low-use areas (P=0.001). In contrast, 1999 low-use areas had greater adult chironomid abundance than high-use areas (P=0.007). The influence of habitat variables on invertebrate abundance and volume was also explored. Aquatic invertebrate abundance was positively associated with high air temperature .in 1998 and 1999. During both years, an increase in aquatic invertebrate volume was associated with an increase in submerged vegetative cover. There was also a positive relationship found between the volume of aquatic invertebrates and their distance from emergent vegetation. Surface insect abundance increased with an increase in the surrounding air temperature, as well as an increase in submerged vegetative cover. Wind speed was the predominant variable positively associated with surface insect volume during 1998 and 1999. The absence of association between aquatic and aerial invertebrates helps illustrate the importance of knowing both invertebrate communities before assessing the suitability of a wetland for brood-rearing. Data from 1998 high- and low-use areas imply that numbers of invertebrates may have been the major determinant of habitat used by dabbler broods. High- and low-use areas in 1999 had similar invertebrate abundances, suggesting other factors played a role in habitat selection. Protection of wetlands with an abundance of both aerial and aquatic invertebrates in addition to adequate emergent escape cover is warranted. Additional research reinforcing the importance of aerial insects as duckling food may provide more insight into their role in suitable brood-rearing habitat