Responses by dabbling ducks and aquatic invertebrates to an experimentally manipulated cattail marsh

Abstract

The responses of dabbling ducks (Anas spp.) and aquatic invertebrates to artificially created cover:water ratios (i.e., 30:70, 50:50, and 70:30) in an overgrown cattail (Typha latifolia) habitat were studied from April to June 1978, on the Delta Marsh in south central Manitoba. Invertebrate populations were not affected by cover–water treatments, but significant temporal changes in population levels occurred. Between 20 May and 9 June, invertebrate levels were higher than during the previous 3 weeks and were higher than levels on the control area of uncut cattail. Dabbling duck pair densities correlated positively with invertebrate levels on treatment areas. Waterfowl behaviour also changed with the increased invertebrate levels. The highest densities of dabbling duck pairs were associated with 50:50 plots, which supports the hypothesis of maximum avian use and production during the "hemi-marsh" phase of the marsh cycle. Explanations for this phenomenon are discussed.