FEEDING HABITAT OF HERONS AND EGRETS ON THE UPPER
MISSISSIPPI RIVER

Christine M. Custer, and Thomas W. Custer. 
U. S. Geological Survey, Upper Mississippi Science Center, P.O. Box 818, La
Crosse, WI  54602-0818 USA

We followed over 700 great blue herons and great egrets by airplane to their
feeding sites from 4 breeding colonies on the upper Mississippi River (UMR)
between April and July in 1995 and 1996.  There was little overlap in feeding
locations between nearby colonies.  More great blue herons left the Mississippi
River to feed during the care-of-young period than during incubation.  The reverse
was true for great egrets.  Water depth and food availability may account for these
differences.  Of those herons and egrets staying on the Mississippi River to feed,
most fed in braided channel habitat below a dam or levee, with fewer feeding
along the main navigation channel or in the open pool.  Those leaving the UMR to
feed went to small creeks or wetlands with fewer birds feeding in farm ponds. 
Herons generally landed on dead or live vegetation mats, bare ground, or on
logs/snags and then either fed from these perches or walked into the water to feed. 
Great egrets, on the other hand, nearly always landed directly in shallow water. 
The implications for feeding site selection will be discussed.

Keywords: feeding habitat, great blue herons, great egrets, Mississippi River

Christine M. Custer, P.O. Box 818, La Crosse, WI  54602.  Voice 608 783-6451,
Fax 608 783-6066, Email christine_custer@nbs.gov

Platform preferred, Poster would be acceptable.