Great blue heron nest (Photo by Don Reimer)
Great blue heron nest (Photo by Don Reimer)
As we approach late June, you may notice that the volume of morning birdsong has diminished to some extent. But certain of the habitual singers, like treetop-dwelling red-eyed vireos, never seem to get the memo, as they broadcast repetitive here I am; where are you? vocals. And robins will continue their larruping dawn and twilight serenades all summer long. Many robin pairs have already produced a first brood and are working on a second. Cardinals are another persistent songster that won’t quit. And those normally noisy blue jays are relatively quiet and secretive these days to conceal nest locations. Subtle but significant nesting activity is now occurring all around us.

Once again, I am involved in the Maine Bird Atlas project, now in its third season. This five-year study aims to “provide a comprehensive understanding of the abundance and distribution of Maine’s bird populations.” On a recent foray, I explored a local heron rookery overlooking a 10-acre beaver flow. Come along, and I’ll narrate the journey.

Great blue herons nest in small, concentrated colonies in isolated areas. And this particular colony met those defining characteristics well, especially that isolation factor. Without the property owner’s guidance, I wouldn’t have found the remote site containing about a dozen nests. Tromping the thick forest cover, a hint of open skyline finally emerged as we neared the beaver impoundment. Throaty squawks and harsh, guttural “kaks” announced the colony’s lively presence. Eight adult herons sat on nests or stood like sentinel statues on adjacent bare branches. Several nests appeared unused, while others contained several chicks in various stages of development. Discounting some remnant downy feathers on the growing chicks, their heavy, spear-like bills were evident. Upon fledging in late July, juvenile birds show a solidly dark cap that differs from the white-crowned adults.

The majestic, widespread great blue is the largest heron in North America. This hardy species arrives in Maine in April to construct or renovate a previous nest in tall trees. Variably placed 20 to 60 feet above ground or water, the male heron gathers materials, while his mate performs much of the actual construction. The resulting platform of sticks is impressively large and bulky. Bits of greenery, such as sprigs of white pine, may rim the nest. Two to seven eggs are generally laid in two-day intervals, which results in the young hatching over a period of several days. Facing competition from larger nest mates, late hatchers have lower odds of survival. Both sexes share in the incubation for about 30 days, and both parents feed the young by regurgitation.

An adaptable and variable diet that crosses several habitat types may account for the species’ broad success. Eating mostly fish, herons also consume frogs, salamanders, turtles, snakes, insects, small birds and mammals. These dietary factors also afford the ability to remain farther north in winter, even in areas where most waters freeze. Occasional herons tallied during Maine’s Christmas Bird Counts will attest to this cold-weather phenomenon.

And, finally, let’s give the beavers their due. Whether you regard them as engineering architects or pesky flooders of forest land, beavers often shape natural settings and play an influential role in determining what birds and animals come to inhabit them. Wetland species, such as wood ducks and mergansers, are direct beneficiaries. Dams are also associated with increased songbird diversity. The eastern kingbirds, common grackles and fishing osprey we observed at the pond’s edge can all thank the beaver for his unflagging work ethic.