Three tall white birds danced along the muddy shore of the Kennebec River in Gardiner last week. They were great egrets, birds just a little smaller than the familiar great blue heron, but all white with yellow bills and black legs. Great egrets are the cousin of the smaller snowy egrets you can sometimes see from spring through early fall along the coast. Snowy egrets, in contrast, have black bills and black legs with yellow feet (“golden slippers,” some birders like to say) and almost never leave coastal locations where there is at least a taste of salt in the water.

Herons and egrets are really both part of the heron family, formerly known as the Ardeidae. The name “egret” has most often been applied to herons that are white although there are some herons that have white forms including the great blue heron (the white form is rather rare) or that pass through an immature all-white phase (the little blue heron). There is also at least one egret (the reddish egret) that can be found in both all-white and darker forms.

Herons and egrets are famous for a somewhat unusual propensity to wander in the post-breeding period. Young birds born earlier in the summer are often found quite far north of their normal breeding range. A few great egrets probably nest annually at one or two islands like Stratton Island, Scarborough, and perhaps Appledore Island, off Kittery, along the southern Maine coast, and birds can be seen feeding  in salt marshes from Scarborough south throughout the summer. But just about every year in late August and, with this year’s lingering hot weather, into September, a few pop up at inland locations in Maine. We often see from one to three somewhere along the Kennebec River between Augusta and Gardiner at least once a year during that season. They hang around for a few weeks and then eventually apparently depart for points south for the winter.

The last two years some colleagues up in the Northwest Territories of Canada have noted a similar dispersal phenomena of great blue heron. Single birds showed up on Great Slave Lake in August and September, many hundreds of miles from the nearest breeding colony down in Alberta. Last year in August, friends in the tiny isolated community of Deliné on the shores of Great Bear Lake (one of the largest lakes in the world and with only this single community of 600 people on its shores) were perplexed to see a bird there that they had never seen before. They sent photos, and it was an immature great blue heron, one of the most northerly records of that species ever in Canada!

Closer to home, a yellow-crowned night-heron has set up shop near the ice pond on Monhegan where it has been enjoyed by birders continuing in September. This is another species that is more common farther south and is looked for by birders here in Maine in the late summer and fall when some disperse north along the Maine coast.

Why do these herons and egrets do this?

One theory is that these young birds are probing the edges of the northern range to learn about and test the conditions. Some pioneering birds just might come back the next year as adults and try to find suitable nesting areas and expand the range northward.

We’ll be watching for “our” great egrets in our area again next year at around this time.

Jeffrey V. Wells, Ph.D., is a Fellow of the Cornell Lab of Ornithology. Dr. Wells is one of the nation's leading bird experts and conservation biologists and author of the “Birder’s Conservation Handbook.” His grandfather, the late John Chase, was a columnist for the Boothbay Register for many years. Allison Childs Wells, formerly of the Cornell Lab of Ornithology, is a senior director at the Natural Resources Council of Maine, a nonprofit membership organization working statewide to protect the nature of Maine. Both are widely published natural history writers and are the authors of the popular book, “Maine’s Favorite Birds” (Tilbury House) and the just-released “Birds of Aruba, Bonaire, and Curaçao” from Cornell University Press.