Cumberland Island Journal

Many people who visit Cumberland are surprised to learn there are mink on the Island.  Most of our guest’s associate this member of the weasel family with more northern locals.  Mink actually range all the way down to South Florida where an endangered sub-species known as the Everglades Mink still manages to survive.  Throughout other parts of the south however the mink is not considered endangered but it’s an animal seldom seen by humans other than duck hunters or fishermen that spend a lot of time in this secretive animal’s wetlands habitat.  Mose people though, have heard of mink due to the fact this animal’s beautiful fur has been used for years to make high dollar garments such as mink coats.  Today captive, farm raised mink have taken over a large part of this market:  one reason is fur coloration can be kept more uniform with ranched animals.  On Cumberland I have noticed fur coloration can vary greatly among our wild mink from dark brown to a rusty red and even orange.  Recently I was with a group of people as we watched a blond two foot long specimen work its way down the river bank on the west side of the Island.  It was the first time I’ve ever seen this color phase.

Mink seem to be constantly on the move; either searching for food and mates or trying to avoid becoming food themselves.  There are a number of predators that will feed on these small animals; hawks, owls and bobcats would all dine on a meal of mink.  But alligators are probably their main threat in our area.  Stomach samples taken from local alligators indicate they frequently take mink.  The mink itself though is a formidable predator for an animal it’s size:  birds, rodents, fish and small crabs are all part of their diet.  Mink cover large territories and many use several denning sites along the way, complicating the efforts of anyone who is trying to observe these illusive animals.

On our Cumberland outings we talk a lot about the Island’s wildlife.  If we can get a glimpse of a seldom seen species it can be a memorable experience for some people and a touch of mink always helps.

While Cumberland Island ‘Greens Up’ in April, so does the nearly 8,000 acres of adjoining Salt marsh.  This is also the month when the bird most associated with these wetlands begins nesting.  Clapper Rails also known as Marsh Hens are a true symbol of the Salt marsh because this is the only habitat they live in; if you study the bird it’s easy to see why.  Rails are laterally thin birds which allows them to move about freely through the thick grasses of the marsh.  Their large feet help them swim and provide support on soft wet ground, while the bird’s long curved bill allows it to probe this muddy environment for it’s main food source, fiddler crabs and snails.

Clapper Rail nests have been described in bird books as grass made platforms on the ground.  However, the one nest I observed was a loosely woven grass bowl in a thick clump of new growth Saltmarsh cord grass about one foot above the ground.  Because this was new spring growth, the nest had been lifted another six to eight inches above the ground by the time the ten buff colored speckled eggs hatched.  Young rails have dark fuzzy feathers and are able to leave the nest and feed themselves within a day or two of hatching.  Although they are tiny and frail looking, the chicks quickly adapt to life in a landscape that floods twice every twenty-four hours with high tides. 

Rails tend to be secretive birds and spend most of their lives hidden in the tall grasses of their environment.  However, they are often seen in early mornings at low tide bathing and feeding along the shore of saltmarsh creeks that border Cumberland.  This time of year as the marsh turns green again and life is being restored there, it’s good to know the hardy little Marsh Hen is an essential part of it.

“Are those bugs all over the ground?”  This is a question I often get when our Island outings pass by a Saltmarsh.  What people are referring to are the great numbers of small fiddler crabs that live in this biologically rich environment.  There are at least three species of fiddlers that inhabit Cumberland’s Saltwater Wetlands.  As the name implies, this crab has a kinship with the fiddle as the large single claw of the male crabs in a way resembles that instrument.  During the warmer months when fiddlers are active, male crabs can be seen waving this pronounced claw in the air in an effort to attract females for breeding and to keep other males out of their territory.  Fiddlers feed mainly on detritus, a mixture of decomposed organic material, mostly grasses produced in the marshes.  These prolific crabs have specialized mouth parts that can seperate the organic food they ingest from the mineral sand, which is spit out in the form of small round pellets.  This feeding behavior qualifies the fiddler as a slow land builder.  Over the years I have come to realize these little crabs play a big roll in the ebb and flow of the Saltmarsh Eco-system.  For example:  many animals eat fiddlers.  Along with several species of wading birds, mammals such as mink and raccoons feed heavily on this abundant food source at low tide, when the muddy ground in the marsh becomes exposed.  During periods of high tide, several species of fish as well as the much larger blue crabs eat fiddlers.  So fiddlers fill a niche here between detritus and numerous predators.

Fiddler crabs most likely to be seen along the edge of a Saltmarsh are the colorful Sand fiddlers also known as Chinabacks:  so named because of the intricate designs on their shells that look like painted porcelain china.  As these roughly one inch long crabs gather along the Saltmarsh shoreline they are easy to see and sometimes mistaken for “bugs” by visitors to the Island.  However these tiny crabs spend much of their lives burrowed in the mud.  During the colder months when fiddlers are less active they are safer underground.  But as temperatures rise this time of year we see the fiddler on the Marsh.

April is the month when the Islands most colorful bird makes its first appearance  after a migration from the West Indies and Central America.  Painted Buntings arrive to begin nesting on Cumberland.  As in most bird species, male buntings are the ones with the most distinctive plumage.  Biologists believe this is to direct predators away from the females as well as to attract the females to the most colorful males.  Whatever the reason, male Painted Buntings are well named with their bright red, blue, yellow and green plumage; while the females are completely green.  These birds are only about five and a half inches long but so brightly colored they always grab the attention of those who see them.  Unfortunately bunting populations have been decreasing at a rate of about three percent each year.  This is mainly due to the fact they are losing nesting habitat in large areas of their Spring and Summer range on the coast of Florida; areas that have been heavily developed.  On Cumberland however there is still suitable habitat for these beautiful birds, especially in the thicker edge vegetation between forest and wetlands.  This is the type of habitat found around the Greyfield Inn and also nearby Dungeness area; it’s the reason why many species of song birds including buntings are often seen here.

Although Cumberland lies within the Southern temperate climate zone there is a strong sub-tropical influence here and the return of the bunting in spring serve as a reminder of this fact.

Spring is officially here and so are warmer temperatures needed to bring out the reptiles.  Cumberland is home to over forty species of reptiles, the largest and most noteable being the alligator.  This is the breeding season for these top predators so the bellowing roars they make to locate mates will be heard in the freshwater wetlands on the Island.  Alligators are freshwater animals that will venture into saltwater to feed.  During the warmer months they are seen in the saltmarsh and tidal creeks on the west side of the Island.  Some alligators on the north end of Cumberland have been known to enter the ocean at night to feed on large schools of mullet that gather there during the summer months.  But alligators cannot live in a salty environment full time because salt will eventually dehydrate them so they have to make it back to freshwater in order to survive.

As one might expect, we get a lot of questions about these high profile animals such as “How big do they get?”  The largest alligator on record is a 19′2″ animal found in Lousiana.

On Cumberland a twelve foot alligator would be considered a very large specimen.  Under ideal conditions of food and climate, young alligators grow about one foot a year until they reach six feet, then the lengthening process slows down as the animal grows thicker.  The males grow faster than females; in twenty years a male can reach a length of about eleven and a half feet, while a female would only grow to a little over eight feet during that period.  However, both become sexually mature when they are about six feet long. 

An alligator nest consists of a large pile of dead vegetation close to water.  In this mound the female can lay anywhere from 20 to over 50 eggs.  The incubation period is about 65 days and the temperature of the eggs in the nest will determine the sex of the young.  Eggs below 86 degrees will hatch all females while eggs above 93 degrees will be all males.  Temperatures between these two extremes will produce both males and females but mostly females.  This information came from studies of alligators mostly in Florida.

Female alligators are good mothers and are very protective of their nest and young.  The young may stay close to her for up to three years before leaving to find their own new territories.  On Cumberland, once an alligator reaches a length of three feet they have nothing to fear except a larger alligator.  The big ones will eat the smaller ones, especially during times of drought when their normal food supply has been interrupted.

Truly wild alligators shy away from humans but can become aggresive and dangerous if people are feeding them.  Recent alligator attacks in Florida involved these types of habitual animals.  On Cumberland there has been one recorded alligator attack.  In 1989 a man bathing in a freshwater pond was bitten by a six foot alligator that quickly released him after making contact.  However, Island alligators are known to feed on large mammals such as deer, feral hogs and possibly feral horses so a human in the water cound be mistaken for something else. 

The alligator is certainly at the top of the food chain in this region and the undisputed king of the freshwater wetlands.  As such, they have an important niche to fill in order to keep this natural system in balance.  Alligators only feed on other animals many of which are mammals that can over populate.  Without predation, diseases will impact and weaken prey species.  So the alligator helps to level the boom and buse cycles of these animals creating a more disease free healthier environment.

Alligators are also important in other ways.  I have found that many people are fascinated by these animals; whether they be seasoned gator hunters from Florida or tourists from Europe or a northern city in this country.  The fact there are large predators in the wild like the alligator that can overpower and kill a human, has a humbling effect on people.  As a result, many of our guests want to see and learn more about these great reptiles.  Now with the warmer Spring temperatures, alligators are becoming active again on Cumberland Island.

It’s Spring green-up time on the Island as new leaves and blooming plants are evident everywhere.  Cumberland is located in the Southern temperate zone but because of the warming effects of the ocean, many sub-tropical plants thrive here including the Island’s most notable tree, the Live Oak.  Although in the same genus as other oaks, Live Oaks are considered to be evergreens.  Unlike most other hardwood trees, they do not drop their leaves in Autumn and lay barren over the Winter months.  Instead, Live Oaks lose most of their leaves in the Spring at the same time the new leaves and pollen heads are forming.

Live Oaks are the dominant trees on the Island because they can withstand more wind and salt spray than other competing trees.  The horizontal limb growth forms a broad sprawling canopy while the shallow root system spreads out to cover the same distance underground.  This combination works well to stabilize the tree.

These sturdy trees with hardwood and twisted grains were the first important commodity to be harvested on the Island.  In the early 1800’s Live Oak limbs with their natural curves were used for the main structural parts of the old sailing ships.

Live Oaks have an average life span of about 300 years although there are specimens in some areas that are much older.  On Cumberland most of the original trees the early settlers found are now gone.  But a few still remain.  One tree on the Greyfield Inn property has a circumference of twenty-nine feet, and according to researchers from the University of Georgia, is about 350 years old.

Compared to other oaks, Live Oaks are fast growers, so a mature forest of these majestic trees once again covers the Island and Spring is the time when they really stand out with their new bright green leaves.

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.