Wheatlands Grassland Birds – 2013

Part One

In their 2013 breeding enterprise the grassland birds at Wheatlands Farm confounded and amazed. But as Flip Wilson used to say,

“ I’m going to tell you that story , but first I need to tell you this one so I can tell you that one.”

A discussion of grassland birds needs a sketch of grassland history and dynamics, which we cover in this first part; we’ll get to the 2013 adventures of the grassland birds in the next two episodes.

Wheatlands, a 165-acre beef cattle farm in the southern Shenandoah Valley, lies in the rain shadow of North Mountain, specifically to the immediate east of 4463’ Elliott Knob which lofts nearly 3000’ above the Valley floor.  In the lee of that prominence the annual rainfall averages 35 inches, ten inches less than the 45 inches lavished on the rest of Virginia. Thirty-five inches is a moisture regime favoring grasslands over deciduous forest and is only slightly more than the average for the tall-grass prairies that once carpeted Illinois and Missouri and Iowa – with a little help from the grazing ungulates and the peoples who invested in the “millennia of exuberant burning” chronicled by Charles C. Mann in 1491.(www.theatlantic.com/magazine/archive/2002/03/1491/302445)

It would be more accurate to say that at a location in temperate North America experiencing a 35-inch rainfall, woody plant succession is more easily arrested than at 45 inches. However, even at reduced moisture, plant succession is still as certain as gravity unless some force acts to suppress the trees and shrubs.  Humans, sponsoring a rich and mobile protein source in the form of grazing ungulates, have been that force since the Wisconsin ice receded 11,000 years ago. Perhaps for all of post-glacial history humans have managed the North American landscape to create grasslands where practicable, including much of the region east of the Allegheny Mountains and especially , I am inclined to believe, in the rain shadow of North Mountain.  That 20-square-mile enclave is beef cattle country today as it was bison country a thousand years ago. Buffalo Creek has cut a waterway through Little North Mountain creating Buffalo Gap which offered the bison summer grazing in the interior of the Alleghenies. Wheatlands Farm is at the center of North Mountain’s 35-inch rainfall arc.

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I live at Wheatlands, so I muse upon the Buffalo Gap grasslands, their history and their legacy complement of grassland birds. I and a Border Collie named Benson tend a cow/calf herd of Charolais-Angus beef cattle 75 to 100 critters strong.  The Wheatlands cattle, like the bison, are grazers; they eat a mix of grass and forbs (non-grass herbs).  When they discover a woody sapling in a pasture they attack, chomping and stomping, horning and wallowing, ripping off branches and pawing the successional intruder into oblivion. I suspect the bison carried the same genetically-encoded chip on their wooly humps, the innate urge to destroy trees, perhaps sensing that trees are a threat to their grassland "salad bar" (a Joel Salatin term. Joel also lives and raises cattle in the North Mountain rain shadow).  The cattle may be desperate for shade but they will not suffer a sapling to grow in their pasture. Moreover, they eventually kill even the mature trees by clustering under them, rubbing off the bark, and compacting soil at the roots.

My interpretation is subjective, but the bovid inclination to work in concert with fire-wielding humans to create and maintain grasslands is clear enough.  I am comfortable with the conclusion that grasslands in temperate North America and other locations, modern and past, are typically the result of the ancient alliance of humans and bovid ungulates – cattle (genetically, auroches ) and bison. Remove the bovids from the equation and humans have no incentive to burn (or mow). Remove the humans and the bison (or cattle) eventually face reduced rations or at least a shift of diet to browsing, which requires a different gut chemistry than is typical of bovids. Remove both and the land reforests in half a human span (Godfrey, 1980).

From the standpoint of grassland birds, grazers are a blessing, if mixed. As they can stomp woody saplings they can also stomp on-ground nests. But as they munch along they tend to leave a grass/forb stand of varying heights which accommodates the birds’ foraging and nesting needs. Dr. Scott Pendleton, a veterinarian in Cadiz, Ohio, monitors Upland Sandpipers and Bobolinks on reclaimed mine land in Harrison County. He notes,

“All the successful Upland Sandpiper and Bobolink nests I have seen on these reclaimed mine lands are in sections which the mine owners lease to local farmers for grazing. The birds need stands of varying heights and densities which the cattle create. The challenge is to encourage farmers to delay mowing to let the birds complete nesting.”

Call the grasslands a stool, if you will, of the kind that furnishes seating and requires three legs – people, ungulates, and a group of birds which are obligate grassland breeders.  If the grasslands and the grassland ungulates knew a close ecological kinship with the humans of olden times so must the grassland birds. Over the millennia the Meadowlarks, the Grasshopper Sparrows, the Bobolinks, the Dickcissels must have been co-passengers with the bison on mankind’s grassland rollercoaster.  Management by birds of seed dispersal, insect pollinators, and food-source insects (grasshoppers et al) are surely vital functions in grassland economics, perhaps of importance equal to the contributions of people and bovids. The entire avian cohort must have learned to balance in the shifting winds of human-created grasslands in North America, riding waves of tribal warfare, weather events, climate shifts, and developments in food-production technology.  We must have in mind that pre-Columbian native populations in North America were large -- 20 to 40 million people at times (Mann, 1491)-- and the ability, the need, of those populations to manipulate the landscape carried massive ecological impact. Trackless virgin forests? Forget it. Even in the East. It is much more efficient to harvest bison in large herds on open grasslands than individual deer skulking in forests.

A hypothesis emerges; like the bison and the grasslands themselves, the grassland birds must operate in  a confederacy with mankind. Over time (people have been in North America for at least 16,000 years) the grassland birds have followed moccasin and hoof through wealth and want, shifting their ranges and schedules and diets with the fortunes of the grasslands of human creation. We see our birds, our surrounds generally, through a squinty lens of 500 post-Columbian years.  That is a very short slice (maybe 5% of the whole salami) of the era of people and their grasslands in North America. The dynamics have always shifted and calamity is likely no stranger, but it seems justifiable to see at least a blur of birds and bison on mankind’s grasslands over 500 or so human generations. 

A Krakatoan blast hit North America’s grasslands after 1492 in the form of diseases distributed by the Spanish.  Very quickly, most of the native human population was dead. There was no immunity to the new pathogens and there was little immunodiversity in the native genetic endowment because the natives of the Western Hemisphere were descendants of a small number of adventurers who crossed the Bering Land Bridge. In Guns, Germs, and Steel Jared Diamond reports,

"Throughout the Americas, diseases  introduced by Europeans spread from tribe to tribe far in    advance of the Europans themselves, killing an estimated 95% of the pre-Columbian  native American population. The most populous and highly organized native societies in North America,  the Mississipian chiefdoms, disaappeared in that way between 1492 and the late 1600s, even before Europeans themselves made their first settlement on the Mississippi River. "

The scheme which had created and maintained the grasslands must have collapsed abruptly. Much of the continent, especially the well-watered East, quickly reforested.  Some understand the volume of atmospheric carbon sequestered in this sudden reforestation to be sufficient to account for the 200-year global temperature drop beginning in 1650 known as the Little Ice Age. By the time the English took an interest in penetrating the continent’s interior in the early 1700s a newly established canopy covered dark corridors of forest that shrugged as if to ask “Grasslands? What Grasslands?”

In the 1700s the English, and others, cleared a lot of forest and created a lot of new grasslands.  By 1900, 75% of the Piedmont was under plow or pasture.  In the accounts of A.C. Bent, the grassland birds recovered somewhat.  But by 1980 only 25% of the Piedmont was cultivated – we, especially we southerners, abandoned our farms wholesale and put them in the hands of the wood products companies creating a desert of row-planted pines.  The grassland breeders vanished from those lands.  Bent refers to a reduction in the Dickcissel’s presence in the East beginning in 1900; the 1980 edition of Peterson’s Field Guide to the Birds notes “formerly bred along seaboard Mass to S.C.”  The Dickcissel, an obligate grassland breeder, has responded to the abandonment (and reforestation) of eastern farmland by vacating much of the East. Other grassland endemics, including Bobolinks, are reduced as well.

Another disruption now threatens the grassland birds – climate change.  Beginning in 2011 and through the 2013 nesting cycle, there has been chronic drought and fire in the Dickcissel’s core breeding range, the traditional prairie grasslands.    The results are apparent in one corner of one valley in Virginia and probably at other locations to the east of the Alleghenies. An informed argument (Kaufman, private correspondence, 2011) suggests that drought-associated pressure on the core breeding range in the Great Plains forced some of the birds eastward. For the first time since 2000, Wheatlands hosted Dickcissels in 2011, probably a half dozen, then more than two dozen singing males in 2012. Numbers were down in 2013 to the 2011 level as the drought shifted westward.

We can hope that the Dickcissels that fled the western droughts in 2011-2013 to nest in the southern Shenandoah Valley may rekindle an interest that will persist even when drought spares the West. That depends on the health of the eastern grasslands and on the compatibility of our farming methods with the birds' breeding needs – in other words, the Dickcissels not only need to nest in the East, they need to nest successfully to recruit a cadre committed to the East.  Because nearly all remaining eastern grasslands are on active farms under intensive production, many nests go through hay-making machinery.

   

In the next two parts of this post we will detail the 2013 nesting cycle of the Bobolinks and Dickcissels at Wheatlands. Their unexpected schedules and behaviors may add an increment to our understanding of these birds with an ancient link to man.