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One of my favorite birds on Cumberland is the Oystercatcher. These attractive shorebirds with their formal black and white markings and bright red bills are always an eye catcher on the beach. As their name implies, they feed on oysters as well as other shellfish.
The hunting skills these birds have particularly becomes apparent when they feed on oysters. On a falling tide, when these shellfish first become exposed to the surface many of them are still partially open while still feeding. The Oystercatcher, with surgical precision, can insert its blade-like bill into the narrow opening of an oyster, cut the abductor muscle and extract the animal. This adaption for shucking oysters makes the Oystercatcher unique among shore feeding birds.
Oystercatchers are starting to pair up now on Cumberland and will be nesting soon on the beach. Their nest is just a depression in the sand, usually somewhere between the high tide line and the fore-dunes. It’s because of this birds’ nesting locations they are now considered to be a species of critical concern. Many of the isolated beaches where Oystercatchers once nested have now been developed; so like many animals, they are losing habitat. But on Cumberland Island there is seventeen and a half miles of undeveloped beach that will always remain that way; protected, as a National Seashore, and a refuge for among other things, the unique Oystercatcher.
If you walk down the beach on Cumberland Island you will eventually come upon the shell of a horseshoe crab. Sometimes visitors encounter large numbers of these ancient animals beached along the shore. Horseshoe crabs which are more closely related to spiders than crabs have been around for over 400 million years according to fossil records, and have not changed much in form over the last 200 million years. They are true survivors that have made the right biological adaptations to face their environment. Along with a total body covering shell they have a protective copper base blood that allows them to live on the bottom of the surrounding shallow seas where there are heavy concentrations of bacteria. Because they are such a unique animal they have become the focus of a lot of research and several medical uses have been found for their blood.
But horseshoe crab populations have been impacted along the east coast for a number of reasons. In come cases, they have been used heavily for bait in blue crab traps. However nothing is isolated in nature so there are other animals that depend on them. Shore birds in particular rely on horseshoe crab eggs for a food source. Some species like dunlins and red knots time their migrations around the spawning of these crabs in the mid-Atlantic states. during this period large numbers of mating pairs come ashore at the waters edge to deposit and fertilize their eggs. On Cumberland Island however the mating activity is much more sporadic. The horseshoe crabs found on the beach are more likely to be individuals washed up by storms or simply animals that moved onto the beach at high tide and were stranded as the tide receded. Horseshoe crabs also molt, so the old shells they discard come ashore as well. After molting, a horseshoe crab can be twenty-five percent larger than it was before.
One interesting note: I have found some biologists reluctant to refer to horseshoe crabs as primitive animals. This is due to the fact that they have made few if any evolutionary changes over the course of millions of years. On the other hand, relative new comers such as mammals including humans are still evolving. But unlike other animals, humans can rapidly alter the environment. Time will tell if both humans and horseshoe crabs will be able to keep up with the rate of these changes.
March 13,2008
March can be a windy month on Cumberland and these conditions often make our morning birding tours a challenge. But even on windy days we can usually find some wildlife activity. While migratory songbirds become difficult to spot, shore birds are easily observed, gathered in flocks facing into the wind trying to maintain feather alignment and conserve body heat.
Strong winds associated with large weather fronts will change the feeding patterns of some animals like white-tailed deer. On Cumberland deer generally do not move around as much during windy conditions. But they can be seen feeding before and after extended periods of rain even if it’s very windy.
Strong winds after a soaking rain have a dramatic effect on the island’s dunes. The drying ability of moving air over wet pliable sand creates a rippled surface revealing a sence of order to the semmingly chaotic winds.
The winds also influence the tides. Strong easerly winds produce higher than normal tides while strong westerly winds expose much more of the beach by making tides lower than normal. The long term effects of wind is most noticeable on plants grwoing near the beach. Severely wind pruned live oak trees lean to the west after years of exposure to prevailing easterly winds.
To a large part, Cumberland is a product of the wind. This fact soon becomes apparent to island visitors any time of year they may be here.
March 5, 2008
It’s March and a wide variety of migratory birds are showing up on and around Cumberland including a large number of lesser Scamp. These handsome ducks with their blue bills are rafting up in the sea close to the beach. On the Island however, the main show is with our resident population of wild turkeys. Now begins the breeding season for these colorful birds with their gobbling and showy courtship displays in the forest, fields and dunes of the Island.
The comeback of the wild turkey in North America is a real success story as conservation practices regarding these native birds have greatly improved in recent decades. On Cumberland, turkey populations were once decimated by over hunting. Sometime during the mid 1900’s though, Island resident Lucy Ferguson re-introduced wild turkeys to the Island with wild birds from the nearby mainland. Today, Cumberland has a thriving wild turkey population.
The wild turkey is only native to North America, where the population is divided into five separate sub-species. Cumberland happens to be located in a region where two sub-species come together: the eastern to the north and the Osceola, or Florida wild turkey from further south. The birds on Cumberland actually have some plumage characteristics of both. The domestic turkey everyone is familiar with came from a sub-species that was captured in Mexico by early Spanish explorers and taken back to Europe where it was domesticated.
Wild turkeys are preyed upon by other animals, especially the young birds, but according to publications by the National Wild turkey Association, predation alone is not a determining factor of turkey populations. However, diseases are: diseases like Avian Pox carried by mosquitoes and Black Head disease carried by chickens can greatly alter the number of turkeys.
Prominent wildlife species such as wild turkeys are always the subject of many tales and stories. One story with some validity to it was that Benjamin Franklin wanted the wild turkey to be the national symbol. Another story is the turkey was looked down upon because they do not mate for life like the chosen symbol the bald eagle. What ever the case, the turkey didn’t make the cut. After observing the same turkeys on Cumberland for many years I can say they do attempt to mate for life, just not with the same partner, and this is the time of year they do it.
