August is the month when birds start to do strange things. May features the influx of migrants. June is dedicated to baby-making. July is all about baby-raising. For the first half of summer, birds arrive at their breeding sites, and stay there. But August brings post-baby weirdness. It’s time for birds, young and old, to spread their wings and fly – both literally and figuratively. They wander.
You can watch it happening right now in Bangor’s Essex Woods. It’s the wetland next to I-95, below the sledding hill. It can be reached via Watchmaker Street from Essex Street, or via Garden Way, just off Drew Lane, near the Bangor Mall. Every August, great egrets move in. In some years, snowy egrets move in, too. The egrets will grab your attention, because they are large, white and not present through the first half of summer.
The egrets don’t nest in Essex Woods, nor anywhere near Bangor. They breed in southern Maine, notably in Scarborough Marsh near Portland, Weskeag Marsh in South Thomaston and a few other coastal marshlands. After nesting, they engage in what ornithologists call “post-breeding dispersal.” Rather than simply heading south for the winter, they spread out in all directions, with some flying north. Besides Essex Woods, they’ve been popping up at various other locations in eastern Maine. Alert readers have been sending me photos from throughout the Bangor region, asking “What is this bird doing here?”
There are many likely reasons for post-breeding dispersal. One obvious possibility is that they’ve eaten much of the available food where they nested. After feeding themselves and hungry kids in that one spot for several months, they may have simply exhausted the all-you-can-eat buffet. Once the kids are sufficiently grown, egrets can wander out to other marshes that might be inadequate for nesting, but terrific for feeding. They may even discover new marshes to colonize in the future.
Dispersal ensures that parents aren’t competing with their own kids for food. Remember that the breeding season begins with just the two parents occupying a territory. But by August, there may be two adult egrets and up to six youngsters trying to feed within the same territory, competing against all the other families doing the same.
Post-breeding dispersal has been studied in other animals as well. Typically, it’s the young that move on, obligated to search for their own territories once they’re old enough to breed. Beavers do this. One study documented dispersal behavior among red squirrels, and found evidence that mother squirrels dispersed so as not to compete with their own kids.
Most shorebirds nest in Canada’s arctic tundra. Southbound migration begins immediately after the chicks hatch. Among many shorebird species, one parent, then the other, leaves before the young have even learned to fly. This is more evidence that some species avoid competing with their own offspring for food. We mostly see migrating adults around Bangor at present, with more immature birds closer to Labor Day. Greater and lesser yellowlegs are early southbound migrants, and they’re turning up now. Solitary sandpipers are often seen in Essex Woods this time of year; adults first, younger birds later.
Along the coastal mudflats, we’re entering peak season for least and semipalmated sandpipers. Semipalmated plover numbers are likewise peaking. These shorebird species also migrate, with adult birds leading the way, followed by their offspring later in summer.
Other birds that nest in Canada are arriving offshore. Red-necked grebes are typically among the first migrants. Grebes are aquatic diving birds that typically nest on freshwater, and winter on saltwater. Although red-necked grebes breed exclusively in western Canada, many head east instead of south, arriving on the Maine coast right about now. The smaller horned grebes arrive a few weeks later.
However, one wayward grebe is further proof that weird things can happen this time of year. A Clark’s grebe has turned up on Togus Pond near Augusta. Clark’s grebes are larger than red-necked grebes – nearly the size of a skinny loon. They nest on freshwater lakes and marshes throughout the west, but rarely get east of the Mississippi River. One turned up in Owl’s Head in March 2005. Now this one. These are the only Clark’s grebes ever reported anywhere in New England.
So, birds are moving around. A lot. Eventually most will fly south, but not before possibly wandering north or east. Some are fleeing the tundra. Some are fleeing their kids. Some are just settling in for the winter. Anything can happen, and it probably will.
Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at firstname.lastname@example.org.