Flight Lines: The water giveth and it taketh away
With a spare moment last week I decided to check on the only great blue heron nesting area that I am aware of in Cass County. A handful of miles south of Galesburg just inside the county line, a small grove of cottonwoods have, for several years, provided a home to many pairs of this large wading bird, creating a small nesting colony known as a rookery. Upon arriving this day, though, it was apparent that no nests were present. Plus it looked as if there may not have been any last year either.
Great blue herons (Ardea herodias) spread out across nearly the entire lower 48 states during spring and summer making these tall—nearly four feet--gray-blue birds easily recognizable and familiar to most Americans. Their long legs and long sinewy necks help make this the tallest North American heron. Adults show a wide swath of black feathering over their eyes with a white cap and a hefty daggerlike bill similar to that of a common loon.
This is also a bird that is easily identified at great distances while flying. At first glance one notices a large dark bird in the sky and might think "eagle" or "vulture." But a more careful look reveals a tucked-in neck, gangly trailing legs, and slow ponderous wingbeats that seem to connote a lack of urgency. In addition, a heron flies with its wings held in arches like a rounded "M," a stark contrast to the long, straight, plank-like wings on which an eagle flies.
Usually seen singly or in small spaced groups, herons often stand stock still along the edges of ponds or lakes or step slowly and purposefully in the shallows, awaiting prey to happen by. The bird eats mostly fish and amphibians but is a formidable predator and will eat nearly anything including birds and mammals. Due to its S-shaped vertebrae, and not entirely unlike a viper, a great blue heron can uncoil and strike quickly, securing a meal firmly in its large bill before swallowing it whole.
I had heard of but never witnessed its mammal-eating habits until a couple of years ago when I walked a rural road along a pasture east of San Diego. Close by, a lone heron alertly stepped its way through some closely-cropped grass paying particular attention, it seemed, to disturbed soil where a gopher might be found. It didn't take long before the bird struck and seized a ground squirrel of significant size, and then swallowed the hapless critter headfirst in lurching gulps. This particular heron was apparently quite practiced in the art of gopher hunting.
With great frequency I encounter great blue herons at Fargo's sanitary lagoons north of town and wonder where these birds are coming from. I have found research that concludes they fly as far as 18 miles in extreme cases to forage. That would seem to indicate a rookery somewhere within that distance from Fargo but I am not aware of one. Might I simply be encountering unmated, non-nesting birds?
Herons usually nest within a couple of miles of a foraging area. Around here that means a wetland of some sort. Sure enough, the Cass County site had a cattail-lined slough within shouting distance of the cottonwoods. Now, however, it has dried up.
Don't look now but the bounty of life boosted by over 20 years of better-than-average moisture in this area might be coming to a halt as most of the state has been under drought conditions for many months. Just a couple of years ago, for example, a person would expect to find Nelson's and Le Conte's sparrows in their tall moist grass habitat here in Cass County. Today they are extremely scarce.
Another possible reason for the collapse of the colony might be harassment. Biologists have found that, in the wake of heavy bald eagle predation on adult herons and their young, rookeries are often abandoned. It's no secret bald eagles are steadily increasing around here.
All told, it might be a combination of factors that has led to the loss of the colony but we won't know. I do know one thing: Great blue herons, like most other organisms in this world, are quite adaptable to changing environmental conditions. They've seen dry spells before, they've dealt with predators before, and they've withstood myriad stresses over millennia that we can only imagine. Yet they've surely survived; just as surely as there will be another great blue heron colony in Cass County again someday.