Bulrush Mediation Effects on Wave Action: Implications for Over-water Nesting Birds

Many species of waterbirds nest over-water in shallow lakes and marshes in the Northern Plains region of North America. High winds are common in this region and the resulting waves can cause significant loss of nesting platforms, yet the behaviour of waves in these systems has not been well-studied. We used observational and experimental techniques to examine how Hardstem Bulrush (Schoenoplectus acutus Muhl.) impacts wave attenuation through its clonal growth characteristics. The predictable growth patterns influence nest placement and nesting success in colonial nesting grebes and other over-water nesting waterbirds. We constructed an artificial nesting colony to experimentally test how location with respect to wave-exposure affects nest structural integrity in grebes. Additional experiments with boat wakes confirmed the importance of emergent vegetation in attenuating waves caused by watercraft. Nests gain more protection from being placed on the lee side of a stand of vegetation than by having denser vegetation right at the nest. Over-water nests that are more protected from wave action by vegetation are at least three times more likely to hatch eggs than more exposed nests.