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• • • 5 At both Peltier Lake and Smith Slough rookeries, great blue herons were more likely to land on the shoreline or on vegetation and walk into the water to feed than were great egrets (Table 4). Great egrets were more likely to land directly in the water than were great blue herons. Because great egrets often feed with other egrets, the water depth is "known" to them because of the other egrets already feeding in the area. Great blue herons, however, often feed solitarily and therefore have no indication of water depth. Hence, they land on a shoreline, vegetation, or other substrate and them walk into the water from there. Great blue herons can also feed from those perches. Table 4. Landing substrate used by great blue herons and great egrets in the upper Mississippi River basin, 1998. Landing substrate Colony & species Vegetation Shoreline Water Logs/snags Tree Other Peltier - Great 9%1 27% 36% 18% :;a % •.: 49/0 9% blue heron �,.,.� Peltier -Great 19% 31% 27% 8% 15% 2 egret Smith Slough • 20% 32% 30% 10% 8% Great blue heron Smith Slough • 4% 13% 63% 4% 13% 2 %3 Great egret Verrnillion - Great blue heron 12% 59% 21% 9% Are 4 herons that plunged to feed and 1 that landed on a man -made structure. 2 Are 4 egrets that landed at an upland site which was probably a roost. site 3 Is 1 egret that landed on a muskrat house A feeding strategy, plunge diving, was used by great blue herons from Peltier. This was included in the "other" category in Table 4. This was a novel feeding strategy that had been seen by the author very infrequently at the other 8 rookeries where the author has worked. This feeding strategy was seen quite commonly at Peltier rookery. When using this feeding method, a great blue heron would fly slowly over the water and then drop into the water to catch a fish. The bird would then rise from the surface of the water, and it had caught a fish, return to shore so that the fish could be swallowed. This feeding method seems to require calm water with fish routinely feeding near the surface.