Big Cats vs. Crocodilians

The Mcbrides track cougars (Puma concolor) for the Florida Department of Natural Resources.  Roy Mcbride began tracking Florida panthers in 1972 when there was some doubt over whether this species still existed in state.  (The Florida panther is the same species as the cougar but I prefer using the latter common name.)  A few years ago, the Mcbrides interrupted a cougar feeding upon an alligator it had killed.  They treed the cat and examined the alligator.  Cougars were known to occasionally prey on smaller alligators, but the Mcbrides were surprised at the size of this specimen.  It measured 8 feet, 8 inches–the largest gator ever known to be killed by a cougar.  The cougar had eaten the brisket (chest area) of the gator but was so spooked by the trackers it never returned to the carcass.  The Mcbrides published their discovery in the Southeastern Naturalist.  Below is the 1st page of the 2 page article.

Cats are courageous hunters. Still, it seems unexpected that they would take on such a dangerous choice of prey.  Nevertheless, caimans make up a significant portion of the jaguar’s diet in certain parts of the Amazon jungle.

Jaguar killing caiman.

Leopards and tigers rarely prey on crocodiles, yet they have been recorded slaying them.

This leopard actually dragged the crocodile from the water onto land and killed it.

Youtube video of a tiger killing a crocodile.

A big cat’s strategy for hunting a crocodilian is cunningly effective.  They attack from behind, get a good grip on the reptile, and bite through the braincase, killing it instantly.  They don’t just ambush crocodilians sunning themselves on the riverbank.  The leopard in the above photos dove into the water and yanked the crocodile from its own element.

I wonder if saber-tooths (Smilodon fatalis) ever attacked alligators.  Saber-tooths had a weaker bite force than any species of extant big cat.  Their big canines would have been at risk of breaking, if they tried to bite through an alligator’s skull.  However, they were very powerful and would have been capable of rolling the alligator on its back and slicing through its throat with their fangs.  Jaguars were 1 of the most common large predators in southeastern North America during the Pleistocene and undoubtedly took a toll on alligators here then.

Reference

Mcbride, Roy; and Cougar Mcbride

“Predation of a Large Alligator by a Florida Panther”

Southeastern Naturalist 9 (4) 2010

Alligator and Heron

I once proposed that alligators saved all terrestrial life on earth.  An adult alligator establishes a territory and digs a deep hole in a marsh or swamp where water pools deeper than in the surrounding environment.  These gator holes help them survive droughts and cold fronts, and they also attract other aquatic animals such as fish, frogs, turtles, waterfowl, wading birds, raccoons and other mammals.  Following the fiery K-T impact 65 million years ago, all the dinosaurs died, but crocodiles and alligators along with the animals that sought refuge in their holes, survived.  Everything above ground literally cooked in the superheated atmosphere caused by the friction of asteroid fragments igniting oxygen.  I shared my hypothesis with a paleontologist, but she was skeptical.  She acknowledged that freshwater organisms suffered a lower extinction rate than dry land and marine species.  However, she didn’t think my hypothesis was testable.  Maybe, it’s an exaggeration to claim that alligators saved all  terrestrial life, but ecologists agree they play a crucial role in fostering wildlife populations in the modern day world.

Gator hole in the Big Cypress Preserve in Florida.

The presence of alligators is beneficial for heron and egret rookeries.  Herons and egrets nest in trees located in wetlands, particularly on islands surounded by alligator-patrolled waters.  Alligators do feed upon the occasional nestling that falls from the nest, but they also take a heavy toll on raccoons, opposums, and even bobcats that would otherwise swim to the island, climb into the rookery, and feast on the eggs or nestlings.  The herons in turn benefit the alligators because their manure fertilizes the water and this increases the abundance of fish.

Heron rookery in Venice, Florida.

Alligator tearing up a possum.  Possums are notorius egg-eaters.

The great blue heron (Ardea herodias) is one of the most spectacular birds of America, and they are common–I see them quite often everywhere.  Green herons (Butoroides stroutal) are supposed to be the most common heron, but I’ve only seen them a handful of times.   Great egrets (Cameroides albus) are about as common as great blue herons, though they seem more tied to larger bodies of water.  By contrast, I’ve seen great blue herons flying over busy highways and hunting in small creeks.  Little blue herons (Egretta caerulea) are supposed to be uncommon, but I’ve seen them more often than I’ve seen green herons.  I saw a yellow crowned night heron (Nyctocorax urolicea) for the first time this summer at Wakulla Springs, Florida.  It was shy and ducked into the weeds.

Great gray heron catching a European rabbit in the Netherlands.  Great blue herons also prey upon rabbits and rodents.  Audubon kept a great blue heron as a pet.  His children were upset when it swallowed their sleeping pet cat.

Yellow crowned night heron with a crayfish.

Scientists studying the Clarks Quarry fossil site near Brunswick, Georgia expressed surprise over the relative lack of abundance of alligator fossils, though the site yielded plenty of remains of aquatic birds.  Alligator fossils were found here, just not as many as one would expect.  Random chance may explain why there were fewer alligator fossils than expected, but I recently realized a possible alternative explanation.  Fossils from Clarks Quarry date to ~14,000 calender years BP.  This was before sea levels and the water table rose to  those of the present day.  Between ~30,000 BP-~7,000 BP, swamps and other wetlands where alligators thrive were rare relic habitats.  Moreover, winters were harsher and summers cooler, even in south Georgia during much of this era.  Alligator populations were at a low ebb in Georgia during the Ice Age.  Yet, they continued to live in low numbers wherever suitable habitat remained.  Alligators withstood the fire of the K-T impact and the icy dry conditions of the Pleistocene.  They are amazing survivers.

When Pleistocene Megafauna Roamed Interdunal Wetlands

My parents used to own a beachfront condo on Harbor Island, South Carolina.  One year, I was surprised to find a freshwater marsh in front of the condo, complete with cattails, frogs, and red-winged blackbirds.  The marsh was located behind a beach dune where it did not exist just a year earlier.  This type of environment is known as an interdunal wetland, and they can form rapidly.  The East Beach freshwater marsh on St. Simon’s Island formed in just 2 months.  Rain washes beach wrack (dead plants and detritus) into the swales between dunes, creating enough topsoil for freshwater species of aquatic plants to take root.  Heavy rains keep the marsh wet, and the dunes prevent drainage.  The water table at sea level is often close to the surface, and because fresh water is lighter than sea water, it remains on top, providing habitat for fresh water species.

Whitney Lake on Cumberland Island, Georgia.  Note the alligators.  It’s a freshwater interdunal wetland with an outlet to the ocean.  Storm surges of saltwater that kill woody plants keep it open.  The state of Georgia has the least developed coast on the Atlantic side of North America.  Most of Georgia’s barrier islands are not accessible via automobile.

Aerial photo of St. Catherine’s Island, Georgia.  The brown represents upland maritime forests of live oak, loblolly pine, and palm trees.  The green represents freshwater, brackish, and saltwater marshes.  About 40,000 years ago sea level was near  present day sea level and some of this island consists of sediment accumulated then.  Then, as the ocean receded, that sediment underlay oak hammocks  surrounded by miles of grassy savannahs.  About 6,000 years ago, sea level rose to this approximate location again and sediment is currently accumulating and building on the old Pleistocene sediment.

Interdunal wetlands located behind beachfront dunes may form rapidly, but they can also be short-lived.  Storm surges can breach beach dunes, resulting in an influx of salt water, followed by drainage.  However, storm surges may play a role in maintaining older freshwater marshes located in the middle of a barrier island well away from the beach.  The influx of salt water kills shrubs and trees.  Eventually, rainwater reduces salinity and shade-intolerant aquatic vegetation becomes re-established.

Feral horse drinking water from Whitney Lake on Cumberland Island.  Interdunal freshwater ponds acted as an oasis for Pleistocene megafauna surrounded by unpotable ocean water and salt marshes.  Horses and hogs run wild on some of Georgia’s barrier islands today.  The presence of megafauna on barrier islands during the Pleistocene wasn’t a problem because natural predators controlled their populations.  Today, large herbivores can overgraze vegetation and cause harmful erosion unless human hunters or wranglers take action.

Freshwater ponds and marshes on barrier islands are like an oasis surrounded by undrinkable ocean water and vast salt marshes.  During the Pleistocene these sources of fresh water would have attracted every species of megafauna living on a barrier island.  Giant ground sloths, mammoths, mastodons, bison, horses, tapirs, llamas, peccaries, deer, capybara, and giant beaver were all drawn to the drinkable water and highly edible plants that grew in the marshes.  Predators, such as dire wolves and big cats, would have lain in wait at these water holes.  The location of interdunal marshes may explain the abundance of Pleistocene fossil sites in this region.  There are 9 above sea level, Pleistocene-aged fossil sites near the Georgia coast (Fossilosa, Isle of Hope, Mayfair, Porter’s Pit, Savannah River dredgings, Turtle River dredgings, Clark’s Quarry, and Watkin’s Quarry) compared to 3 sites in the Ridge and Valley Region and just 1 site in the Piedmont Region.  Animals attracted to freshwater marshes occasionally died there and were buried by sediment carried by storm surges.  This combination of factors explains why there are more Pleistocene fossils found near the coast than anywhere else in the state, though there are other depositional origins for some of the sites here as well.

Today, megafaunal species living on Georgia’s barrier islands include white-tail deer, feral horses and hogs, some exotic species of introduced deer, and alligators.  Paleontologists have noticed the relative lack of alligator fossils found in the Pleistocene sites near the Georgia coast, where they would be expected to be abundant.  Apparently, alligators did range here during the Pleistocene, but it may be that egg-eating mammals kept their populations in check.  Jaguars probably directly preyed upon adults.  Interdunal wetlands also host marsh rabbits, raccoons, mink, otters, wading birds, ducks, and songbirds that would otherwise be absent due to the lack of freshwater.

Mosquito fish (Gambusia holbrooki).  It’s well adapted for life in interdunal wetlands.  They are related to those tropical aquarium favorites–guppies.

Killifish, mosquito fish, top-nosed minnows, mullet, and gars thrive in interdunal ponds.  Mosquito fish are well adapted for this type of environment.  They eat their own weight in mosquito larva everyday, giving them the energy to reproduce rapidly–a population of 7,000 can increase to 120,000 is just 5 months.  This allows them to quickly colonize newly created marshes and improves their chances of survival during storm surges.  Mosquito fish can endure high temperatures and high levels of salinity that would prove fatal to most other species of fresh water fish.  Bream are also found in some interdunal ponds, but scientists don’t know whether they occur naturally or were introduced by man.

Botanists recognize 4 successional stages of interdunal wetlands.  The first is an open water stage with floating plants such as duckweed and emergent vegetation including cattails, pickerel weed, and arrow-arum.  The second stage has less open water and is dominated by cattails and pickerel weed.  The third stage is a grassy shrub stage with saw grass (of Everglades fame), cordgrass, sedges, buttonbush, rose mallow, and wax myrtle.  The final stage is a woods of red maple, Carolina willow, tupelo, and water oak.  A storm surge of saltwater can kill the trees and return the marsh to the open water stage.  Below are some photos of some shrubs commonly found in interdunal wetlands.

Buttonbush (Cephalanthus occidentalis) is common on the edges of interdunal wetlands.  A study of fossil mastodon dung found buttonbush to be a common item in their diet in Florida.  Mastodon foraging faciliated the spread of the seed-filled buttonballs which float.  A mastodon tearing apart a buttonbush was beneficial to the plant species’s long term survival.

Carolina willow (Salix caroliniana) with egret nests.

Wax myrtle (Myrica cerifera).  The wax rendered from the berries is used to make candles.  Euell Gibbons states that the leaves can be used for seasoning soups and stews, like bay leaves. 

Rose mallow (Hibiscus moscheutos), a common and beautiful plant found growing in interdunal wetlands.  The roots were used to make marshmallows.  All modern marshmallows sold in grocery stores are made artificially without mallow roots.