Habitat Variety and Bird Abundance
Part of the Young Naturalist Awards Curriculum Collection.
Over the past three years I have been privileged to observe Lake Wildwood fluctuate through three distinctive habitats. The original habitat was a full, man-made lake. The next habitat consisted of lake bed mudflats. The last habitat was a marsh. Finally, a return to the normal water capacity eliminated the marsh, thus completing the cycle. The habitat change began in September 1995 and ended in January 1998. Optics, a sketchpad, and a notebook aided me in recording bird abundance throughout the period, normally in the late afternoon. Two specific locations offered me a consistent vantage point of the lake. Each particular habitat attracted a different set of birds. Bird species used the lake when new sources of food and habitat favored their characteristics.
September 1995 ushered in an unprecedented season for herons, egrets, and shorebirds. The lake was lowered to install a pipeline along the southern edge of the lake and to desilt the "fingers" area of the lake. With the flood gate open, water began to recede. Five new species inhabited the newly exposed mudflats and shallow pools: great egret, snowy egret, little blue heron, blue-winged teal, and pectoral sandpiper. Rocky Creek continued to flow through the lake bed. The muddy creek water abounded with captivated fish.
The many eyes of egrets and herons intently watched the water for trapped fish. A great blue heron glided on its long legs with measured steps. With the aid of keen eyes and an outstretched neck, the heron struck and pierced a fish with its bill. Flipping the pierced fish into the air, the heron adroitly caught the airborne fish between its long mandibles. Pointing its bill upward, the heron positioned the fish into a headfirst descent down the throat. The neck bulged as the fish oozed into the crop.
Great blue herons and great egrets continued to inhabit the mudflats though the winter. Their numbers were not as high as in September because the fish population had declined. The original trapped fish had either been devoured by birds, or had died from lack of a suitable habitat. Thus, while a change in habitat may favor a new species, it may be to the demise of the original occupant. Killdeer, greater yellowlegs, and common snipe also occupied the 186-acre mudflat, feeding on invertebrates and arthropods. Puddles of water surrounding the continuously flowing Rock Creek attracted mallards, permanent residents of the lake. Canadian geese, hooded mergansers, along with several unusual Bonaparte's gulls, still found enough open water to feed. Eight new bird species were recorded using the water pools and mudflats during the winter, including gadwall, lesser yellowlegs, and American pipit.
Many species benefited from the concentration of dying fish. I observed a red-shouldered hawk eat a dead fish on March 3, 1996. With a fish in its talons securely fastened into its prey, the raptor devoured the fish piece by piece. Later that month I spotted another bird of prey taking advantage of the habitat change. While scanning the lake bed, interspersed with cut tree stumps, a few rusting barrels, discarded tires, and winding depressions, I noticed a large brown bird sitting on the mudflat. Was it a turkey vulture? Yes, and it was eating a dead fish! The fish was most likely a grass carp from its large size. Never before had I seen a vulture on the ground anywhere in the vicinity. Later, the vulture with evident exertion took flight on that storm-threatened evening.
I again observed turkey vultures on the ground in November 1997. On my way to the marsh near dusk one crisp, clear day, I unexpectedly discovered a thrilling sight. Looking up from the ground, I was startled to see a turkey vulture one hundred feet from me. Half raising its wings, the bird almost flew. The dead branch swayed under its weight, however, the bird did not fly. A tall, gnarled dead oak tree behind the closest bird hosted twenty turkey vultures and ten black vultures. Although they eyed me suspiciously, they continued preening. After five minutes, I slowly unpacked my scope and began sketching. A putrid smell began to become more obvious. Then I remembered the source of the smell. I had found a deer carcass here one week ago. Black vultures also took advantage of a road-kill beaver during November. By providing habitat for the beaver and deer, the lake indirectly supported vultures.
The resonance of musical gurgling and croaking filled the sky. My excitement rose while I scanned the sky with 10x42 Leica BA binoculars to locate the flock of gray long-necked birds. I was enthused when I observed the sandhill cranes close over the treeline. They were going to land! After several circles, the thirteen birds came to their resting point on the mudflats of the half empty lake. Elegantly placing each foot forward with precision, the flock spread out to feed. They did not stalk like a heron; they fed by foraging the surface of the mud. The tall, gray, slender birds each had a bustle created by wide and curved tertian feathers. A beautiful bare red forehead and crown adorned each bird. The date was February 26, 1996. The mudflats once again provided a new location for birds to feed and rest.
Sandhill cranes have a unique 100-mile-wide migration path through Middle Georgia. The eastern United States population spends a brief winter mainly in Florida and then migrates to the Northern Great Plains for the summer. I have seen them on the ground only three times in Bibb County.
The lake was lowered to a greater degree in April. That event saved the life of a red bat on April 2, 1996. On the main beach while drawing mallards early in the afternoon, I heard American crows calling raucously. Two crows were swooping and diving at some erratically flying creature. Was it a bird? No, it was a bat. Each bird took turns nabbing and harassing the bat. The bat fell to the mud below. The two American crows apparently had no desire to eat the bat, so they promptly left. I pointed my telescope to the red-colored bat. Ten minutes passed. Still the red bat did not move. Assuming that it was dead, I returned to drawing mallards. Movement from the bat's location attracted my eyes to the mud. The bat was flying! I followed the bat in my telescope to the shore, where it landed on the bark of an oak tree covered with ivy. The bat would have drowned if the water level had been higher. The change of habitat from lake to mudflats certainly bene-fited this little creature.
An abundance of plant growth became obvious in early summer. The moist lake bed provided optimum conditions for the germination of marsh seeds. The lowering and refilling of the lake unintentionally followed the pattern of impoundment drawdowns. National Wildlife Refuges and duck clubs often manage impoundment and ponds in this manner.
The dry upper edges of the lake bed near the main beach supported a nesting pair of killdeer. Like fiddler crabs of the Georgia Coast, the killdeer chicks scurried from place to place, behind their ever-watchful parents. When threatened, the fledglings retreated to the thick vegetation in the middle of the lake bed. Other than providing protection for common birds, would the marsh attract previously unrecorded species? Yes. I found a nesting pair of common moorhens, a first occurrence in Bibb County. In Middle Georgia they are rare visitors, appearing mainly in May and December. The moorhens were fond of shallow flooded areas of chufa, bulrushes, and cattails. Clucks and harsh squawks from the moorhens, piercing clucks from the green herons, and high-pitched whines from insects reminded me of the sensation of being in the Okefenokee Swamp. Large numbers of birds, such as the six green herons, did not necessarily prove that the overall bird population was increasing, but that abundance of food caused the concentration of birds.
With maintenance work completed, the flood gate was closed. Slowly, the lake began to refill from rain and the influx from Rocky and Colaparchee Creeks. It did not completely fill until early winter. The habitat was used extensively by dabbling ducks during the winter of 1996-1997. I found 15 species of ducks at Lake Wildwood, the most abundant of which was blue-winged teal. Quibbling, high-pitched calls of the teal added much to my enjoyment during the fall. Numbers peaked in early October when 320 birds occupied the marsh. Northern shovelers were regular visitors to the marsh. They fed by skimming their broad bill back and forth on the surface of the water. Males arrived in their eclipse plumage, retaining their splotchy appearance until late winter. I also recorded up to four northern pintails at the lake nearly every day from late September to mid-February. Pintails are rather uncommon winter visitors in Middle Georgia. Up to 446 American Coots inhabited the lake in January 1997. This marsh habitat would prove to be only temporary. The change of habitat to the original water level would eventually eliminate the healthy marsh. Without the marsh, the lake could no longer provide the optimal habitat and food for dabbling ducks.
The spring of 1997 ushered in a different era for the lake. The marsh had receded hundreds of feet. Double-crested cormorants were the most abundant species at the lake. One hundred fished the lake in late March. A killdeer pair raised another brood, although without the protection of the vegetated lake bed. Again, four chicks were raised. One day I could not locate the fledglings. When I finally looked at the adult, I saw ten legs under its body! All four chicks were hunkered down under the parent bird, hiding their heads in its belly feathers. Over the next two weeks this behavior was noted several more times. The fledglings were quite round with long legs. They only had one black breast band. Several weeks passed before the second band appeared. Their tails resembled scuffed up, frayed brooms. Propelled by their greenish-gray legs, the chicks ran from spot to spot searching for anything that moved. Erecting its body, one fledgling uttered a week "kil-dee." The adults, however, were quite loud. The killdeer has a very descriptive Latin species name: vociferous.
Yet while many bird species shifted in numbers over the three-year period, belted kingfishers did not fluctuate. A pair could always be found fishing the lake. In the spring of 1995, I located a kingfisher tunnel in a clay bank about 100 feet from the lake. It was not an active nest, as it had spider webs in the entrance. In April 1996, I again checked the nest because of adjacent kingfisher activity. The nest was still vacant. However, when I turned around to climb down the bank, I noticed another hole in the opposite bank. Eagerly, I checked it. Two depressed grooves receded into the obscure dark tunnel. I had found an active nest! The bird's stout, short legs and feet had created the "railroad tracks." Although I checked the nest several more times that spring, I never saw a kingfisher enter it. A year later, while drawing near the bank, I observed a female fly into the new tunnel of last year! A few days later, determined to see the bird enter the tunnel with my scope, I hid in the woods near the bank. With my telescope aimed at the hole, I waited. Soon the bird flew up to the power line near the nest. Its harsh alarm alerted me to its presence. Because it did not tolerate even my concealed presence, it promptly left. A few days later I again waited for the bird. This time, however, a car was my blind. My eyes were trained on an old work sign, "Lake Wildwood Boating Areas," because this site was a favorite perching location. Arriving on the sign with a fish, the male kingfisher let out a rattle, raised its crest, and quickly flicked its tail upwards. At the latter part of the rattle, its tail eased down to the original position. Powerful, quick strokes of the wings propelled it to the nest tunnel. Yet it did not immediately enter. The kingfisher landed on a pine tree branch above the bank. Intently it observed the surrounding area. It finally flew into the dark tunnel. The parents would always enter the nest cautiously. Two young fledged at the end of April. During the mudflat stage of the lake the kingfishers fished Rocky Creek extensively.
The presence of varying sources of food attracted migrants during the fall of 1997. Restocked fish attracted a migrating osprey for four days in August. It was a creature of habit. If it was not fishing, it was sitting on a tall, slender dead tree at the extreme west end of the lake. While it often tolerated my presence, it made its aversion known by its strident call.
Chufa and other marsh grasses had declined throughout the summer. The few remaining plants of chufa attracted a spotted sandpiper, which ate the seed. Incessantly bobbing its tail, the sandpiper would travel the length of the beach for food.Another reason for the diminishing marsh was the introduction of grass carp. However, a remnant of the marsh was still intact in the fall of 1997. In contrast to the daily observations of pintails the year before, only one pintail was seen. The high count of blue-winged teal was only 56 birds, a low count. Although the rising water diminished dabbling duck habitat, it returned the lake to the habitat favoring diving ducks, specifically the ring-necked duck. Ring-billed gulls also inhabited the lake in high numbers.
Unintentionally created by man, the habitat at Lake Wildwood became a haven for a variety of wildlife during the past three years. Each habitat change benefited certain birds. No one habitat can support everything; habitat diversity is the key to abundant and prolific wildlife.
Bibliography
Berger, Andrew J. Bird Study. New York: Dover Publications, 1961.
G. Paul, An Annotated Checklist of Birds of Middle Georgia. Macon, Georgia, Unpublished. 1997.
Haney, J.C., et al. Annotated Checklist of Georgia Birds. Georgia Ornithological Society occasional publication. No.10. 1986.
National Geographic Society. Field Guide to the Birds of North America 2nd edition. Washington DC: National Geographic Society, 1987.
Peterson, Roger Tory. Eastern Birds. Boston: Houghton Mifflin, 1980.
Readers Digest. North American Wildlife. Pleasantville, NY: Montreal, 1982.
United States Department of the Interior. Waterfowl Tomorrow. Washington, DC: United States Government Printing Office, 1964.