Piedmont Cliff Ecology

Cliffs represent some of the most pristine natural environments left in the temperate zone .  Developers have little use for them, though some are transformed into stone quarries and ruined.  Cliffs are the best examples of environments that have remained unchanged since the Pleistocene.  Aside from a few bird extinctions and extirpations, they host about the same ecological communities now as they did a million years ago. 

Cliffs are common in the Blue Ridge Mountains of north Georgia but many are found in the piedmont region of the state as well.  Cliffs located in the piedmont offer the southeasternmost available habitat for species that depend upon this type of environment.  In the piedmont cliffs consist of erosion resistant rock that forms vertical or almost vertical bluffs adjacent to rivers.  There are cliffs along the Chattahoochee and Flint Rivers.  Some cliffs are mountains that rise well above the surrounding landscape.  Currahee Mountain in Stephens County, the southeasternmost extension of the Blue Ridge Mountains, rises 800 feet above the surrounding landscape.  Big Mountain in Oglethorpe County is 100 feet higher than the local topography.  Pine Mountain in Harris County reaches an altitude of 1,395 feet above sea level and has many cliffs.

Currahee Mountain in Stephen’s County.  It is located in the piedmont, just a few miles from the Blue Ridge region.  Note the radio towers.

Chattahoochee River Bluff. 

Sprewell Bluff adjacent to the Flint River

Tallallulah Gorge.  This is in the Blue Ridge Mountains, not the piedmont.  I visited this site in the Summer of 2004 before I started writing this blog.  I remember descending a stairway to the gorge and coming face to face with a black vulture, a species confortable at such heights.

Cliffs adjacent to rivers provide ideal nesting and roosting habitat for many species of birds.  Nests located on cliffs are difficult for mammalian predators to access.  The vantage point of a cliff allows predatory birds, such as peregrine falcons, to see potential prey on the river below.  Flying insects abound over river water, attacting swallows and bats.

Black vultures and turkey vultures use cliffs for roosting and nesting.  During the Pleistocene California condors, terratorns, and possibly Grinnell’s crested eagle used cliffs in Georgia.  However, most species of vultures also make use of tree snags.  Formerly, the peregrine falcon almost exclusively nested on cliffs.

Peregrine falcon nesting on a building in Atlanta.  These falcons use skyscrapers as a substitute for cliffs.  The skyscrapers mimic their original preferred habitat.

The peregrine falcon (Falco peregrinus) is also known as the duck hawk because ducks are a favored item of their diet.  They formerly were common in north Georgia where cliffs are abundant and likely nested as far south as the piedmont cliffs.  J.J. Audubon reported seeing 50 peregrine falcons on a 4 month trip down the Mississippi River to collect bird specimens, but I’ve never seen one in the wild.  They were extirpated from the state about 100 years ago–hunters used to shoot birds of prey for the hell of it, causing the local demise of golden eagles as well.  But with the help of recovery programs, they’ve returned to the state.  Instead of re-occupying natural cliffs, they’ve taken residence on big city skyscrapers that mimic their natural habitats.  They find plenty of prey in city pigeons which were also originally cliff dwellers.

Peregrine falcons are spectacular birds capable of reaching a speed of 200 mph when they are descending upon prey.  They usually attack flying birds, especially ducks, pigeons, blackbirds, and blue jays.  They are the only predatory bird crows are afraid to mob.  The chimney swift may be the only bird fast enough to outmaneuver it.  Peregrine falcons aggressively take over cliff nesting sites, chasing away not only all ravens but eagles 4 times their size.  There is a case on record of a peregrine falcon killing a golden eagle by chasing it into a cliffside.  The following youtube video shows a peregrine falcon knocking out and probably killing a red-tailed hawk that ventured too close to its nest. http://www.youtube.com/watch?v=Hpz66RYD110

J.J. Audubon observed peregrine falcons learning to associate the sound of a hunter’s shotgun with a dead duck.  Peregrine falcons frequently used to steal ducks dispatched by human hunters.  One individual falcon learned to enter a hole in Audubon’s pigeon coop and began taking a pigeon every day until Audubon shot it.  Audubon noted that peregrine falcons eat dead fish, but apparently they don’t normally prey upon mammals or reptiles.

Golden eagle feeding on a red fox that it killed.

Golden eagles (Aquila chrysaetos) primarily nest on cliffs and also formerly ranged into Georgia.  Eagle Mountain, Georgia may be named for the golden eagles that used to nest there.  They take large prey for a bird–juvenile deer, turkey, goose, raccoon, and skunk, but they mostly feed upon rodents and rabbits.  Bald eagles like to nest on cliffs too but will more readily build big stick nests in trees.

Cliff swallows building mud nests.

Cliff swallows (Petrochelidos pyrrhonatus) build mud nests on the sides of cliffs and catch insects flying over water.  They’ve learned to build nests under bridges all across the state, and I see them flying in the vicinity of just about every bridge I drive over during summer.

Ravens formerly nested on Georgia’s cliffs but are now considered rare stragglers in state.  Other birds that like to nest on cliffs include red-tailed hawks, great horned owls, barn owls, eastern phoebes, Carolina wrens, goldfinches, grackles, and mourning doves.

Some mammals reside in cliff environments.  Bats roost in overhangs, rock shelters, and caves.  Raccoons, woodrats, and chipmunks can climb to dens less frequented by predators.  Cougars are also known as mountain lions because they have enough agility to climb cliffs where there are safe denning areas for kittens.  During the Pleistocene other big cats and dire wolves would not have been able to reach these dens.  The ability to traverse rugged terrain gave cougars an advantage over other larger predators then and may explain why they were able to co-exist with low populations of humans for so long when other carnivores weren’t.

Enough soil washes onto ledges that plants can take root.  Lichens cover exposed rock.  Chestnut oak, sand hickory, winged elm, red maple, red cedar, shortleaf pine, and Virginia pine grow on cliff ledges in the Georgia piedmont.  So do shrubs such as blueberry, century plant, rhododendron, and mountain laurel. Povery oat grass, bluestem, rock-pink, violets, Carolina lilly, coreopsis, and rockcap fern are some examples of ground cover decorating cliff ledges.

References:

Audubon, J.J.

Audubon: Drawings and Writings

Penguin Books 1999

Larson, D.W.; Uta Matthes, and Peter Kelly

Cliff Ecology: Pattern and Process in Cliff Ecosystems

Cambridge University Press 2005

Tags: Big Mountain, Chattahoochee River Bluff, cliff swallows, Currahee Mountain, Falco peregrinus, golden eagles, Mountain lion, peregrine falcon, raven, Sprewell Bluff, Tallullulah Gorge