Comments by Carrol Henderson on the Great Blue Heron Rookery
COMMENTS BY CARROL HENDERSON REGARDING THE GREAT BLUE HERON COLONY AT ROCHESTER, MINNESOTA. May 3, 2021.
I would like to provide these comments regarding the significance of the great blue heron colony located southwest of Rochester that is currently threatened by development. I visited this colony on Tuesday afternoon, April 27, and had the opportunity to view the herons at their nest and see the area of the colony that had been flagged by the developer for cutting the trees that would have been used for nesting by the herons.
Comments of the homeowners who had herons nesting on their property stated that the herons had been nesting as early as the 1950s, so the colony was likely active for 60 years or more. This is a very long time for a heron colony to sustain itself.
It was also apparent that there had been no loss of trees in spite of the long life of the colony. Typically, the excrement of heron droppings will increase the acidity of the soil and contribute to the death of the nesting trees. However, this has not happened to the trees in this colony.
The sloping topography of the colony site suggests that the acidity caused by the herons’ excrement and the amount of rainfall in the area flushes the acidity from the site and prevents death of the nesting trees. Most heron colonies are on flat terrain that results in death of the trees in the long term.
In 1980 I organized a volunteer survey of heron colonies with DNR wildlife biologist Katherine (Hirsch) Haws and we determined that there were 151 great blue heron colonies in the state. All the heronries in the state were either in dead trees in beaver ponds, on islands or peninsulas on lakes, or on the edges of lakes and rivers. None of the heronries were in mature upland hardwood forests. During the Minnesota Breeding Bird Atlas project conducted from 2009 to 2013, 90 great blue heronries were identified. None of those colonies were in mature upland hardwood forests. Conservationist Don Arnosti viewed the colony last week and determined that the trees in the colony included oaks, older aspen, black cherry, and understory trees of ironwood. To the best of my knowledge, this is the only great blue heron colony in Minnesota that is in a mature upland hardwood forest. The special features that I have mentioned above demonstrate that this is a unique natural resource feature both for Olmsted County and the state of Minnesota.
It is also important to note that the Minnesota Breeding Bird Survey that is sponsored by the US Fish and Wildlife Service has shown that Minnesota’s great blue heron counts have shown a steady decline of -1.32% per year every year since 1967. While these herons are not listed as threatened or endangered, this decline is troubling and could likely result in their being listed in future status assessments.
I would respectfully recommend that this colony be protected by a collaborative conservation effort that could include designation as a state Scientific and Natural Area (SNA).
Biography:
Since 1977, Carrol Henderson is recognized for his accomplishments in developing and implementing a statewide program for nongame wildlife conservation in Minnesota that has received national and international recognition. He studied zoology, botany, and physics at Iowa State and received a master’s degree in ecology and wildlife management from the University of Georgia in 1970. During his service in charge of the Nongame Wildlife Program he initiated projects for the reintroduction of Trumpeter Swans, River Otters, and collaborated on the reintroduction of Peregrine Falcons, conservation of Bluebirds, research on Bald Eagle lead poisoning, and contaminant studies on Common Loons resulting from the Deepwater Horizon oil spill. Carrol is the author or coauthor of 13 books which have sold over 300,000 copies. All the royalties from his DNR books have gone to the Nongame Wildlife Program.
Photo by Michael Melford