6th Annual Judith Ramaley Celebration of Research and Creative Scholarship
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Poster #52 Assessment of Great Blue Heron nest sites within the Mertes Slough Heronry Reese J. Glaser and Heidi S. Hickey Faculty Mentor: Neal Mundahl The Mertes Slough heronry in the Upper Mississippi River National Wildlife & Fish Refuge near Winona, MN, has been occupied by great blue herons (Ardea herodias) since 1977. Numbers of nesting herons have varied widely during that period, and the heronry location has shifted slightly. The objectives of this study were 1) to assess the current forest overstory used as nest trees and the forest midstory growing in as replacement nest trees; and 2) to document nest placement and clustering within nest trees. Nineteen variable radius plots were established evenly throughout the heronry. Overstory trees within each plot were counted, identified, and measured (height, diameter), and midstory tree species were recorded. Heron nests were counted and their heights were measured. Seven species of trees were represented in the heronry overstory, but silver maple (Acer saccharinum) dominated (85%) the community. Six species were recorded in the midstory, with silver maple (located in 79% of plots) and American elm (Ulmus americana, 37% of plots) being the most common. Heron nests were located in 40% of the overstory trees surveyed, with nest trees (95% silver maple; remainder green ash and eastern cottonwood) averaging nearly 5 m taller and 28 cm greater in diameter than non-nest trees. Most nest trees contained multiple nests (average 3.3 nests/tree, range 1-11 nests/tree), with nests averaging 16.1 m off the ground (range 8.2-23.2 m). Nest height was strongly correlated with tree height (linear regression r2 = 0.65, P < 0.001), with nest heights averaging 78% of tree height. Preferred nest trees appear to be plentiful in the shorter overstory and mid-story forest within the heronry, suggesting adequate nesting habitat for future generations of great blue herons. |
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