Great Blue Heron

The Great Blue Heron is by far the most familiar and widespread member of its family in New Hampshire. It nests either singly or in colonies of up to a hundred (or, rarely, more) pairs, usually in wooded swamps but occasionally on islands. Colonies are generally over water to minimize the risks posed by terrestrial mammalian predators. Their bulky stick nests are most easily seen when built in dead trees in beaver ponds or other open wetlands. A colony may persist in a location for decades, but over time dead trees (or their branches) fall and make the site less suitable and the herons are forced to shift elsewhere.

Disturbance and predation can also sometimes cause herons to abandon a colony during the nesting season. For this reason, it is recommended that human activity be minimized within 200-300 yards of an active colony. Generally, pedestrian intrusion is less disruptive than machinery, but there is a huge range of responses depending on habitat and disturbance type. As for predation, while their nest sites serve to minimize the threat from mammals such as raccoons, danger from above is another matter. While crows and ravens take a few heron eggs, the greatest threat comes from Bald Eagles. Eagles will readily kill nestling herons and even adults, and can cause significant colony disruption where they are common. In fact, rapidly growing eagle populations in Maine may cause ongoing heron declines and possibly lesser recent declines in New Hampshire.

Although nesting is localized in colonies, Great Blue Herons forage widely, sometimes travelling up to 10 miles in search of food. For this reason you can readily find them in areas without colonies, such as ponds in the White Mountains or along the seacoast. Numbers along the coast in late summer and fall are supplemented by post-breeding movements by herons from within and outside of the state. When there is open water, herons often remain along the coast or southern river valleys well into the winter.

Fish comprise the primary diet of the Great Blue Heron, but they have been recorded eating a wide variety of other items. Frogs are common, with other items including snakes, invertebrates, small mammals, and even birds. They have been recorded capturing and swallowing birds as large as Pied-billed Grebe and Least Bittern. This probably should come as no surprise considering the size of some fish herons have been seen to consume. Sometimes herons will specialize on small mammals when they are abundant. A notable anecdote involves one in a New Hampshire yard systematically depleting the local chipmunk population over a few weeks.