In researching birding behaviors, I learned that great blue herons create their nests in rookeries. Here in Central Iowa herons prefer sycamore trees for their communal nesting sites. This particular rookery consists of about 50 nests in four sycamore trees in close proximity to each other. At two herons per nest, there are approximately 100 herons that populate this rookery. This time of year herons are working on their nests. To do this, the male heron flies to a nearby area and either finds a stick on the ground or breaks one off a tree. He then flies the twig back to the nest and gives it to the female who uses it on the nest. Ornithologists believe that the main reason for communal nesting is due to a scarcity of nesting areas that are isolated, near an abundant food supply, and contains tall trees. By living in large groups there is cooperative protection of their young from predators. If a hawk or raccoon is seen stalking a baby heron several adults in the colony will physically attack the predator. This is called “mobbing”. With their long, dagger-like bills, a heron can easily kill most predators. Herons are mostly monogamous during a breeding season, but choose new mates every year. In watching the herons for 90 minutes this morning, there was seldom a 15-second period where there wasn’t at least one heron in the air returning to a nest with a stick.
