Thirteen years ago, a violent storm with a massive tornado tore through North Minneapolis, leaving a swath of destruction in its wake. Numerous people lost trees, had their roofs removed, or their homes destroyed. Walls were reduced to matchsticks.
Among the casualties was a sizable Great Blue Heron rookery lodged in a cluster of trees edging the Mississippi River at approximately 4900 Mississippi Drive. The rookery took a direct hit. Not a nest remained, and dead and injured chicks lay scattered about the river banks. The storm hit at the height of the heron breeding season and could not have caused more damage. However, in the ensuing years, the birds demonstrated their resilience by establishing a new rookery downriver at Marshall Terrace Park, or by joining an existing colony upriver at Coon Rapids Dam Regional Park.
Herons nest in rookeries because they’re safe. The nests are placed in trees that often stand in water, making it hard for predators to reach vulnerable eggs and nestlings. Clustered nests mean that there are more than one set of eyes to watch for nefarious interlopers. Other rookeries can be found along the river and its tributaries, among them the large Pig’s Eye Lake rookery, which is closed to visitors during the breeding season.
Locally, there is a rookery on the St. Croix River south of Osceola; and also on West Rush Lake in northern Chisago County on “Crane Island.”
Standing tall at 46 inches, the Great Blue is North America’s largest heron. The species has a large range encompassing most of the continent. Herons nest in fresh and salt water, and they will forage in grasslands and agricultural fields. They also are flexible in their diet. They are frequently seen stalking fish, frogs or small mammals like mice, but will eat anything within striking distance, including reptiles and large insects. They have a large, dagger-like bill that generates great respect among researchers. Humans handling great blues have been known to lose an eye; one tale holds that a direct hit to the heart has killed a researcher, but that could not be confirmed.
Great Blue Herons return to their nests in March, early in spring with ice still covering lakes. Nests are repaired and mates begin elaborate courtship displays. Herons are mostly monogamous during the breeding season, but begin each spring with new mates. The female lays two to six pale blue eggs; both sexes incubate. Incubation lasts 27-29 days; and nestlings spend 49-81 days in the nest for a total nest time of about three months. That’s a long time to attend a nest.
As parent birds feed growing chicks, they forage in wider and wider circles. Observing a well-known rookery in Lake Minnetonka, T.S. Roberts learned that herons from that colony flew to the Minnesota River at Fort Snelling to forage, a distance of 18-20 miles—every day. Residents of southern Chisago County frequently see great blues winging their way northwest to the Chisago Lakes, most likely from the rookery on the St. Croix River. Conversely, herons can be seen flying southeast near sunset, returning home.
By mid-July, the nestlings are standing about in groups on the edge of the nest. Feeding becomes a perilous activity. To fall would most likely mean death, since the parents will not attend offspring on the ground. Roberts described a rookery as “a Great Uproar” resounding with “loud, raucous snarling outcries of the many birds.” He admitted that people might not like to live next to one, but that most appreciate the wild beauty of these lanky, elegant birds.
Once reduced to low numbers because they were hunted for their feathers, Great Blue Herons enjoy a stable population. However, they are vulnerable to habitat loss—like a spring tornado; and human activities, as increasing traffic, logging and motorboats can hinder their breeding efforts.
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