Birds of Indian Subcontinent

Foraging-Niche Dynamics of Gadwalls and American Coots in Winter

Publication Type:Journal Article
Year of Publication:1998
Authors:S. McKnight, K, Hepp, GR
Journal:The Auk
Date Published:1998
ISBN Number:00048038
Keywords:Anas, Anas strepera, Anatidae, Chaulelasmus, Chaulelasmus strepera, Fulica, Fulica americana, Fulica atra, Rallidae, Strepera
Abstract:We examined diet, microhabitat, and feeding method of Gadwalls (Anas strepera) and American Coots (Fulica americana) and their relationships to food abundance during winter to test several hypotheses relative to niche breadth and overlap. Mass of aquatic vegetation declined over time, and interspecific differences in diet and microhabitat generally occurred only when food abundance was low. Diet and feeding-method niche breadths were negatively related to food abundance, as predicted by niche theory. However, microhabitat niche breadth was not related to food abundance. Overlaps in diet, microhabitat, and feeding-method niches were positively related to food abundance, which is consistent with niche partitioning between potentially competing species. Divergence in foraging niches with declining food abundance was related primarily to behavioral differences between Gadwalls and coots. Both species fed predominantly at the surface in areas dominated by Eurasian watermilfoil (Myriophyllum spicatum) in early winter when food was abundant. Most of the Gadwalls left the reservoir when food abundance declined in late winter. Those that remained kleptoparasitized diving coots, or flew to relatively isolated habitats where filamentous algae grew at the surface. Coots, on the other hand, remained in deep-water habitats where they fed by diving for milfoil.
Short Title:The Auk
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith