How Wetland Type and Food Availability Affect Duck Abundance

Summary Boreal wetlands are essential breeding habitats for waterfowl but are increasingly vulnerable to hydrological changes. Despite their importance, temporary wetlands remain relatively understudied compared to permanent wetlands. These differences in wetland characteristics may influence how waterfowl distribute themselves across habitat types. Waterfowl are distributed over different wetland types according to their preferences. These differences are in wetland hydrology, structure and food availability, which determine the suitability of wetland type. This study examined duck abundance in relation to aquatic invertebrate availability in different wetlands in the Evo Natura 2000 area, southern Finland. Ducks were visually observed and counted in four different sessions and invertebrates were collected using activity traps and indexed by biomass proxy. This was executed in 21 wetlands: 7 lakes, 7 beaver ponds and 7 vernal pools. Duck abundance was hypothesized to be the highest in beaver ponds and vernal pools due to higher invertebrate availability. Results revealed that beaver ponds supported substantially more ducks than vernal pools and lakes. No significant correlation was found between invertebrate index and duck abundance. That is because vernal pools had high early-season macroinvertebrate populations but dried rapidly due to low precipitation and lakes showed high zooplankton indices but lower macroinvertebrates indices. Beaver ponds on the other hand, offered stable macroinvertebrate availability and structural complexity throughout the season. Those factors combined, offer possibility for hosting ducks in brood-rearing season. These findings indicate that factors like hydroperiod, habitat size, and temporal stability may outweigh invertebrate abundance in determining duck abundance. Therefore, this study accentuates the ecological importance of heterogeneous wetland mosaics for waterfowl.