Birders across Ohio have been thrilled by an invasion of southern herons that are rarely seen this far north. The source of their excitement? The little blue heron, a denizen of southern swamps.
In a normal year, only a few of these waders make it north to Buckeye country. This year, several dozen birds have been sighted, in nearly all corners of the state. Little blue herons occasionally engage in large-scale late summer and fall northward movements. Such flights are termed post-breeding dispersals.
The reasons for these migrations are not clear, but a likely factor is a diminishment of good habitat in core areas of the breeding range.
Droughts can dry marshes and other wetland habitats, forcing herons to disperse far and wide in an effort to find food. If summer droughts combine with good nesting success in the heronries, the young birds are forced to go nomad en masse.
The little blue heron's main breeding range in the U.S. is in the southeastern Atlantic and Gulf coastal states. These lanky-legged waders occupy a much larger region than that, though. Little blues are primarily tropical, nesting from Mexico and the Caribbean south to Brazil and Peru.
Birds that make it to Ohio - about as far north as the species routinely occurs - are 5,000 miles north of the southernmost populations of little blue herons in coastal Brazil.
Massive irruptions of little blue herons into the upper Midwest are rare, especially in recent decades. The 1920s-30s saw large influxes of herons into Ohio, and 1930 was the biggest invasion year ever.
That year, observers tallied nearly 1,200 little blue herons.
The 2012 little blue heron flight has totaled about 50-60 birds - excellent numbers for modern times, but a shadow of the invasions of 80 years ago.
Most of the little blue herons appearing in Ohio are not really blue - they are juvenile birds, which are white. It would be easy to dismiss one as an egret, and indeed little blues are related closely to the snowy egret.
It takes a little blue heron two years to acquire full adult plumage, at which point they are clad in feathers of rich slatey-blue offset by deep maroon head and neck feathering.
Nearly any marshy wetland where herons congregate might be playing host to little blue herons now.
They'll probably be in association with two of our most common heron species, the great blue heron and great egret. The latter is all white, as are juvenile little blue herons, but that's the extent of the resemblance.
Little blues are far smaller and have dull grayish bills, while the comparatively giant egrets have large dagger-like yellow bills.
A more likely source of confusion is another southern heron, the snowy egret. There have been above-normal numbers of these southerners in Ohio, too, and little blues and snowy egrets often forage together.
Snowy egrets are about the same size as little blue herons, but are easily recognized by the yellow skin between the bill and eye, and black legs with golden-yellow "slippers" (feet).
Little blue herons are fun to watch as they hunt the shallows. A foraging bird moves slowly and methodically, keeping a sharp watch on the nearby waters. Occasionally, it'll stir a foot in the muck to spook aquatic animals to the surface.
Anything small enough to swallow that enters the heron's sphere is fair game: fish, tadpoles, frogs, crayfish, dragonflies, etc.
Our little blue heron invasion began in early July and should continue into September. Keep your eyes peeled for these southern visitors.
Jim McCormac is a wildlife specialist with Ohio Division of Wildlife.
