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 eating an opossum

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.

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4 Responses to “Alligator and Heron”

  1. jamesrobertsmith Says:

    Your proposal is probably not completely out of the question and may be one of the reasons that some animals survived beyond the extinction boundary.

    When I was a kid I read a wonderful book about an alligator. It told in simple terms everything that an alligator did to alter its environment, including widening and deepening pools for dry periods (which benefits many other animals). I’d love to find that book and add it to my library.

    I’ve also found Great blue herons to be very common. I see them everywhere in the low country and even here in the Piedmont. One year when we were in the midst of one of our very bad droughts (I think it was 2002), a stream I had to cross almost ever day slowly dried up, except for deep, isolated pools. The pools were full of fish. One day I noticed a Great blue heron on the creek and he slowly worked his way down the waterway over the course of a couple of weeks, one pool at a time, until he’d fished them all out. He didn’t leave a pool with a single fish in it.

    One day I stopped on the little bridge I had to use to cross that creek while he was fishing the pool beneath it and we just stared at one another. He (or she) didn’t seem to least bit worried about my proximity. One of my favorite birds.

    A park ranger (at Blue Springs State Park in Florida) told me that most people discount the Great blue heron as a predator. But he considered it a top predator and had seen them down animals you would not have thought were in their diet: large turtles, small alligators, big snakes, rabbits, opossum, raccoons, etc.

    • markgelbart Says:

      They’re like dinosaurs.

      I’ve seen great blue herons in the moutains as well.

      Audubon said they were dangerous to handle–they will aim their long bills at a human’s eye and could easily blind a man with an accurate strike.

  2. tai haku Says:

    Hi Mark
    That photo of the heron/rabbit is actually a grey heron and european rabbit – I believe it was taken in the netherlands by Ad Sprang but seems to pop up some times labelled otherwise.

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