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Green herons (Butorides virescens) are here – but not for much longer. After arriving in spring earlier than most other herons – often the fourth week of April – and staying the summer, they fly south from late September to late October. A few stragglers may not leave until November. They head for warmer climes, such as Florida, the Gulf Coast, the Caribbean, Mexico or Central and South America. Who can blame them? Sometimes in the winter, I myself wish I were in one of these places.
Green herons migrate at night, often triggered by the arrival of cold fronts that bring cooler air and winds from the north, after using their time here to breed.
The female lays about four eggs, which hatch in about three weeks. The young, high in trees, become expert climbers. They move among the branches, still covered in white down, before they can fly. According to Bent,
In climbing they make use of their feet, wings and bill, or, rather of the neck, hooking their bills and chins over the branches and pulling themselves up … If the ornithologist climbs the tree in order to observe the half-grown young in the nest, these almost always leave in haste and scatter to the outermost tips of the branches.
When the young are approached too closely, they regurgitate the contents of their crops to the discomfort of the seeker after knowledge, although this action gives the latter an opportunity to learn the character of their food.
Apparently, regurgitation as a defense mechanism is innate. The birds do not have to be taught how to do this:
The brand new baby, who had never been fed, and who had scarcely opened his eyes on this queer world, yet attempted to protest against our meddling by the characteristic heron method of defense. In his case the action was merely a nervous “gagging” and would seem to indicate that this act is involuntary rather than intentional on the part of all herons.
Green herons are about the size of crow, but they can extend their coiled S-shaped neck to a length equal to that of their body. This “rubber neck” helps them stretch out to catch prey, swallow large critters and position their head without moving the body. Green heron necks also have a specialized long vertebra that acts like a hinge, allowing the heron to suddenly snap its head forward with great force and speed. The neck vertebra allows the heron to spear or grab unsuspecting prey.
Herons are unique in other ways too. Underneath their outer feathers, they have special down feathers that are always growing. The feather tips break down into a dust the consistency of talcum powder. Using a claw on its middle toe, the heron collects this powder and works it into its feathers. This powder helps waterproof the bird, and it absorbs dirt on the feathers, making them easier to clean.
Green herons have been known to use tools, a learned behavior of some of the more experienced birds. For example, a heron might notice that a fish gobbles an insect on the surface. The heron might then drop an insect to see if a fish responds. Herons have been known to try to attract fish by dropping pieces of bread, insects or even feathers onto the water’s surface.
It’s a little surprising, then, that they build such flimsy-looking nests – though ones that nonetheless serve their purpose. The female put the nests together after the male chooses a site, often in the fork of a tree, near or over water, and gathers twigs for her. Ornithologist Arthur Cleveland Bent described the structures this way:
The nest itself is a simple affair from 10 to 12 inches in diameter, ill-adapted, it would seem to hold eggs when the tree branches wave in the wind, for it is a flat platform of sticks, destitute of any sort of lining and not cup shaped. Some at least of the twigs composing the nest are green. The nest is so thin and flimsy that one can sometimes look through it from below and see the eggs. In making the nest the herons must weave the twigs in and out to a certain extent, for if they merely laid the sticks one on top of the other, the nest would fall to pieces at the least disturbance.
Green herons used to be spotted all over the Cambridge region. According to William Brewster in 1906,
In midsummer, after their young had become strong of wing, our Cambridge Green Herons were once accustomed to feed in the early morning and late afternoon – as well as at all hours of the day when the weather was lowering – in the salt or brackish marshes along the Charles River. We used to see them constantly in the month of August, passing and repassing low over Brattle Street at various points between Sparks Street and Mount Auburn. They all returned to their roosts in the Fresh Pond Swamps at evening, when the last stragglers sometimes met the first flights of Night Herons moving in the opposite direction. Within the past two or three years both species have nearly ceased to visit the Charles River Marshes.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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