Leggy and elegant, the stately Great Blue Heron cuts a striking figure on Minnesota’s bird scene. We often see great blue herons wading in water on the edge of a pond, rapt and motionless, poised, it would seem, for a kill. Or they appear in the sky, necks drawn into an S-shape, long legs held straight aft, the six-foot span wings beating slow and steady.
Herons are short-distance migrators, coming to Minnesota for the breeding season and flying south in late fall to the mid-to southern part of North America. They arrive in Minnesota in mid-to late March, often before the ice is off the ponds and lakes in which they customarily forage. They are flexible diners, though, and will hunt anything that moves: fish, yes, and also frogs, snakes, grasshoppers and other insects, and mammals that might frequent a marsh, like mice, shrews and small muskrats. They will use their dagger-like bill to impale lunch.
Great Blue Herons are colonial nesters. They build platform nests consisting of sticks and lined with softer material like pine needles, moss and grass high in trees, often 100 feet above the ground. Rookeries are historical with birds returning to the same colony for decades. Colonies are almost always in the wooded part of Minnesota. Often nests are sited on an island, but colonies in tamarack swamps are not uncommon, as well as colonies in woods far away from water. (See previous article). Living in a colony has the advantage of having many eyes on the look-out for predators.
Heron rookeries are notably noisy. T.S. Roberts, writing in 1932 in Birds of Minnesota, visited a famous rookery on an island in Lake Minnetonka. The rookery had previously been on Crane Island, but the building of summer homes on that island had forced the birds to another island. Now, that island was threatened with development and Roberts feared that the birds would be forced out with nowhere to go. Still, on his visit he noted the “loud, raucous, snarling outcries,” especially at night. The clamor “swell[ed]…to proportions that are almost terrifying.” When a parent bird returned to the nest with food, the families were “noisy and boisterous.”
Colonial nesting means that parents must forage far afield to feed their brood. Roberts determined that the Minnetonka rookery residents foraged in the Minnesota River sloughs, as far south as Pike Island, a flight distance of 18-20 miles. On morning walks, I often see herons flying from what I presume is the rookery on the St. Croix River south of Osceola to the Chisago Lakes, a distance of at least 10 miles. The heron on our lake presumably stays the entire day, and departs as dusk for the rookery.
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