by Patrick Higgins

I start looking on Valentine’s Day and saw my first swallow-tailed kite of the season on March 1^st. sailing just above a hammock in the southern reaches of the Park.   It seemed almost paper thin, flashing white then black as it effortlessly swooped, turned and soared, changing direction in an instant with slight adjustments of its scissor-like tail.  Native Americans saw these birds as the Great Creator’s window on our world or as messengers between the world above and ours below. For me too they have a spiritual quality and never fail to bring joy.

My excitement was heightened by the knowledge that this herald of spring had journeyed over 4,500 miles from the Pantanal, a vast Everglades-like wetland straddling the borders of Brazil, Bolivia and Paraguay, to nest here and then would repeat the trip home in September.

Males and females are indistinguishable in size and plumage.  My kite would already have formed a breeding pair during migration and then together sought out a nest site in a tall tree.  In the Fakahatchee swallow-tails favor the very top of slash pines on Four Stakes Prairie.  They usually nest in clusters within a few hundred yards of a couple of other pairs laying 2 – 3 white and brown splotched eggs, which need three weeks incubation. From hatching to fledging takes another 6 weeks, although only one usually survives to this stage – the others having been killed, out-competed for food or pushed out of the nest by the first chick to hatch.

In flight Swallow-tailed kites appear petite and delicate as they perform their aerial ballet, but their wing span is over four feet. They seldom flap their wings, making flight look completely effortless.  They seize prey like dragonflies and wasps midair and deftly pluck tree-frogs, anoles, small snakes, cicadas and baby birds from the forest canopy.  Unlike other raptors they eat on the wing as they continue searching for their next meal, and even drink and bathe on the wing, skimming the surface of ponds and rivers.  They mainly feed vertebrates to their young, but most of the adult’s diet consists of insects.  Due to their aerial prowess swallow-tails have few natural enemies, but are vulnerable to nocturnal predation by great horned owls.

Sadly their distribution in the United States has been steadily reduced by direct persecution in former times and continuing changes in land use and habitat loss.  They now occupy less than 5% percent of their historic range with only a few thousand individuals found in the southeast, Florida and parts of Texas, making each sighting seem even more miraculous.

A mass of wading birds feeding on concentrated prey during the dry-down on the salt marsh south of the Trail. Photo by Patrick Higgins

by Patrick Higgins

Last month I was tearing along Tamiami Trail for an early morning FOF meeting when my eye was caught by one of those Florida spectacles that just stop you in your tracks.  Late or not, I squealed over onto the verge.  Hundreds upon hundreds of birds were engaged in a feeding frenzy in a series of ephemeral ponds stretching southward across the tidal marsh, just north of the East River. Crowds of great egrets, snowy egrets, white ibis, wood storks, cattle egrets and even white pelicans were hobnobbing in the pools.

As they strutted and bobbed they were perfectly reflected in the waters below. There was a constant fluttering of wings and an undercurrent of coarse “arrr, arrr, arrrs” from great egrets, and what sounded almost like a heron being throttled, followed by a hyena-like cackle from the snowys.  Scattered amongst this host were a few great blues, and a few spoonbills, but it was very much a white tie affair. They were gorging themselves almost shoulder to shoulder on the highly concentrated prey resulting from the seasonal dry-down. By my return in the late afternoon the birds had all dispersed.

But 80 years ago a Russian ecologist named Gause developed the Competitive Exclusion Principle. He postulated that two or more species, having identical patterns of resource use can not coexist in a stable environment, as one will be better adapted and eventually out-compete and eliminate the other.  So how do all these different species coexist?

This free-for-all is the exception.  The superabundance had allowed each species to temporarily step out of their niche.  Most of the year direct competition is avoided by resource partitioning. Although the birds share the same habitat, they avoid direct completion by either exploiting different resources, or the same ones but in different ways. This is largely achieved by specialized bill adaptations, varying leg lengths, and differing hunting and feeding strategies.

The ibis (Eudocimus albus) for example feeds by probing with its narrow decurved bill in a frenetic manner. It explores in, around and under obstacles. As a result it captures a higher percentage of invertebrates, typically crayfish and insect larvae in fresh water, and small crabs in salt water. Much of the ibis’ quarry is taken directly from burrows or other hiding places, and this strategy seems equally adapted to our lawns.

The wood stork (Mycteria americana ) typically feeds in water 18” or less with its head down. It’s a grope feeder – swinging its partially open beak from side to side until contact is made. This triggers one of fastest reflexes in the animal world. Its bill snaps shut in 3/100^th of a second.  Sometimes the wood stork also sloshes its feet about to startle prey. Its tactile feeding technique works well in turbid water, but prey must be abundant to be effective and it’s ineffective in clear water as potential prey can see and evade them. Hence their nesting time coincides with the dry-down when prey is concentrated.

The roseate spoonbill (Ajaja ajaja), has an unusual spatulate-shaped bill which it swings from side to side, open-billed and submerged to stir up food as it wades in shallow water.  Like the wood stork when it feels a prey item it snaps its bill closed, pulls the prey out of the water, and swallows it.  Several birds often team-up forming a cooperative line. Most of their feeding is in salt water areas and their food is primarily crustaceans- especially prawns and shrimp, which aids the development of their pink coloring.

The great blue heron (Ardea herodias ) on the other hand by virtue of their large size – up to 4’6”, are able to fish in waters deeper than other wading birds. They are fairly representative of the 12 Florida species in the heron family. They are all visual hunters and mostly tallish birds that tend to stand upright and still in shallow waters or on the shore as “sit and wait predators” staring intently at the water, or patiently stalking through them. When prey is spotted they dart out their long necks to seize or spear it. Great blues tend to be solitary hunters not tolerating the close presence of other birds and are able to tackle larger fish up to 15” or even small mammals.  Some of the other herons may employ lures like the snowy wiggling its yellow feet to attract prey, or the tricolor heron may dash about in a shallow pool, then suddenly stand stock still with its wings out to create shadow to attract the panicked fish.

Resource partitioning may be temporal as well as spatial.  We have two nocturnal specialists, the black-crowned (Nycticorax nycticorax) and yellow crowned night heron (Nyctanassa violacea), although the former is the more nocturnal. Both of these stocky birds have larger eyes to aid night vision, but comparatively short legs for herons.  This restricts them to shallower water. They prefer wading on mud flats and sport heavy shear-like bills to tackle their favourite prey: crabs and crayfish, which they pull apart before ingesting.  Unlike most herons they prefer not to stand in the water when hunting, but to perch on mangrove roots or other objects at the water’s edge, leaning over to seize their prey.

Other wading birds like the limpkin (Aramus guarauna) are even more specialized with a chisel–like bill to tackle their favourite food, the Apple snail. After breaking through operculum,  the snail’s trap door, it slips its lower mandible into the shell to snip the muscle that attaches the snail to its shell and extracts and swallows it whole.  Its lower mandible actually curves slightly to right to accommodate curvature of shell. Although it hunts visually the limpkin can also probe tactilely under surface vegetation and in turbid water. Due to its selective diet it encounters little competition from other wading birds.

Similarly the cattle egret has carved its own niche via its association with cattle and by frequently hunting in terrestrial habitats.  Similarly differences in heron sizes sort them into what depths they can stalk. While diminutive green-backed herons are restricted to hunting on the edge and extreme shallows, great blues can wade out into substantial depths and tackle sizable fish that would be impossible for a greenback to handle.

So while the great blues, greenbacks and snowy egrets pursue fish, white ibis forage for fiddler crabs, roseate spoonbills sift in search of tiny aquatic invertebrates and least bitterns snap at dragonflies, all avoiding direct completion through resource partitioning aided by their specialized bill and other adaptations.

by Patrick Higgins

About 1 ¾ miles up Jane’s Scenic Drive just after the first bend there is a distinct ecotone where the prairie on either side abruptly transitions to forest. You’ve entered Fakahatchee’s strand; the world’s largest subtropical strand swamp and a geological feature unique to southwest Florida that provides habitat for many threatened or endangered species.   Technically a strand is simply a shallow, water-filled channel in which trees are growing. But it’s more than that. The Strand’s canopy moderates extremes, creating a microclimate that retains humidity, making it just a little bit cooler in the summer and a little bit warmer in the winter. This in turn allows a rich community of native bromeliads, ferns and orchids to flourish; it literally drips with life.

180 yards beyond the entry into the Strand, where a culvert passes under the Drive, there’s a small semicircular pond on the right that provides a window into this world. It’s worth pulling over to dwell a while, but best to go on some 20 yards and then double back on foot so you can approach slowly and quietly.

A broad slough spills out of the swamp here before it is channelled under the road.  On this windless early January day mottled grey pop ash trunks and a blue sky were perfectly reflected in the pool below.  Despite the Sun’s glare I could see a school of sailfin mollies (Poecilia latipinna) close by, hanging almost motionless in the 2 foot deep, tea-colored water. This robust native fish is the same that is often chosen for home aquariums, probably because they can tolerate a wide spectrum of conditions from low oxygen to high salinity. Their natural range is a crescent from North Carolina around through Texas to Mexico’s Yucatan, including Florida. Sadly someone thought it would be a good idea to introduce them to California’s hypersaline inland Salton Sea. A perfectly benign species here is now out-competing the endangered desert pupfish (Cyprinodon macularius) there. We can’t leave well enough alone.

Beyond the mollies but still beneath the surface are feathery patches of bladderwort (Utricularia inflata). The whole plant is submerged with only their yellow buttercup-like flowers poking above the surface. Their flimsy roots do little more than serve as anchors.  The plants absorb what nutrients they can directly from the water through their thin cell walls. But the slough’s acidic waters are nutrient poor.

Like some other bog and swamp plants, the bladderwort has evolved a means to supplement this pathway by exploiting the ready availability of essential biochemicals in animal tissue. It is carnivorous. Some of its leaves are modified into bladder-shaped traps to ensnare passing zooplankton and even small fish hatchlings. These operate like the compressed bulb of an eye-dropper. Minute hairs around the bladder’s mouth are touch sensitive. When stimulated they cause the bladder’s walls to relax, sucking in passing prey that is then slowly digested.

At the back of the pool is a rhizomatous mass of emergent vegetation between a wall of heavily buttressed pop ash trunks.  Their buttresses probably serve a similar function to those of cypress trees, helping to absorb oxygen. Today this part of the Strand is a pop ash swamp, but it wasn’t always so. These trees would have been an understorey species before the cypress was logged. Even though logging ended almost 60 years ago the damming affect of the road and the culvert’s channelization has probably kept the water high enough at this particular spot to prevent cypress seedlings from establishing. It’s very hard to undo man’s work.

Something caught my eye at the back of the pond; an almost imperceptible out-of-place shape. The principles of camouflage and concealment from my army days (shape, shine, shadow, sound, movement and color) came seeping back into my mind as I peered harder. Yes!  I could just make out an alligator’s eye ridge barely above the surface. Nearby a darker crouched shape attracted my attention. It was a little green heron obscured behind a tangle of leaves. It slowly emerged, picking its way towards the hidden gator. I suspected that they were both aware of each because it foraged just so close, then changed direction. And when it did so, the gator, now discovered, moved out a little into the open pond to expose and orientate the bony scutes along its back to the Sun and warm up. If dinner was out of reach, there was no point in being cold.

But most notable was that midway up the pop ash trunks, amongst the narrower-leafed cardinal airplants (Tillandsia fasciculata), a scattering of giant airplants (Tillandsia utriculata) still hung on. These bromeliads are ecosystems in themselves.  Their aerial ponds support a microcosm of life.

Sadly these giant tank epiphytes are an increasingly rare sight due to the depredations of the Mexican bromeliad weevil (Metamasius callizona) – an invasive exotic.  This so-called evil weevil arrived in Florida from Mexico on imported ornamentals. The giant airplant is particularly susceptible because of its ‘big bang’ reproductive strategy.

All our other native bromeliads reproduce both asexually (typically by pupping) and sexually. The giant doesn’t propagate vegetatively at all, and only flowers once in its 10-20 year life span, after which it dies. That’s a long time to be susceptible to the weevil with plenty of opportunity for infestation before reproducing. If it does successfully reach this stage, the giant airplant pushes up a huge flowering shoot over 6 ½ feet high in a final burst of energy. This may ultimately bear 10,000 seeds which are then dispersed on tiny wind-borne parachutes.

Several stages of the weevil’s life cycle may be busy eating away various parts of the plant at the same time, but the death blow is when their larvae bore into and shred the plant’s stem tissue to build cocoons. The answer may be biological control. A lot of work has been done on an imported parasitoid tachinid fly, Lixadmontia franki. After extensive testing these have been released in small numbers but rearing them in sufficient quantities has been problematic. You have to have bromeliad weevils for them to prey on and these then need bromeliads to feed on. They’ve tried using trays of pineapple tops leftover from supermarkets for the latter, but the process isn’t completely cracked yet.

The weevil’s devastation has been progressing inexorably southward through the Fakahatchee. But I’m an optimist and like to believe that perhaps the solution lies here in the bromeliad’s gene pool by our little pond. Maybe the random genetic shuffle of sexual reproduction has produced a combination that is somehow resistant in this location. We’ll have to keep observing.

Another possible salvation might be giant airplants surviving in isolated hammocks or cypress domes. The weevil is a weak flyer that travels from branch to branch rather than over long distances and perhaps these reservoirs may serve to repopulate the Fakahatchee in the future.

My thoughts returned to the scene before me and my eyes moved upward to the grass-like tufts of reddish-tinged southern needleleaf (Tillandsia setacea) higherin the trees. Behind them I could just make out the white blotches of several roosting egrets. As I lingered I heard the plop of a fish, then the mutterings of some herons and finally the flap of wings. I turned to leave. On the other side of the road, a limpkin was patiently stalking over some logs floating in our slough which continued ever so slowly to carry the Strand’s waters towards the sea. All this in a fifteen minute stop – that’s the Fakahatchee!

by Patrick Higgins

Photo by Rose Flynn

For a change of scene I decided to visit a cypress dome instead of a prairie hammock. The mid-December day I choose coincided with the passage of a rapidly moving cold-front, so I set off under a grey sky. I had noticed a classic dome on Copeland Prairie on a previous excursion and thought it would be fun to investigate, as domes are really the opposites of tree islands, as I shall later explain. My target was located 1• miles up the track running north from the first bend of Jane’s Scenic Drive.

I had expected the Prairie to be essentially dry like Lee-Cypress across the road, so was lazily sporting calf-high Wellington boots appropriate for muddy English country walks, but which would fill with water if overtopped. As it turned out several inches of water remained, perhaps because of JSD’s damming effect. I found that I had to teeter-totter along the track’s central ridge to avoid sections where the ruts were perilously deep – something I wouldn’t have thought twice about if I was wearing my regular ‘wet’ boots. But this gave me the opportunity to observe the little mosquito fish that had been concentrated in them and only weeks before were spread all across the Prairie.

Photo by Patrick Higgins

Dull light isn’t the best to appreciate the Florida landscape, but to either side, bare hat-rack cypress stood like lonely sentinels. These dwarfs, standing only 10-15 feet high, are stunted pond cypress that eke out a meagre existence on slivers of soil over the prairie’s bedrock and may actually be over 150 years old, deserving our respect. There’s debate whether pond cypress are a separate species from bald cypress (Taxodium distichum) or merely a variety of the same species (var. nutans) but opinion seems to be leaning towards the latter. Whatever the taxonomy, pond cypress do have special adaptations to the harsher niches they occupy, including thicker bark to increase fire resistance and needles closely appressed to their upturned branchlets to aid in water retention, versus the droopy feathery branchlets of bald cypress.

All around me the almost fluorescent, blue, bobbing heads of Glades Lobelia visually popped against the dry grass along with the intense white of String Lilies in their prime. There were still the occasional Grassy Arrowhead in bloom, but these had long peaked and were looking forlorn. Crushed Water Hyssops underfoot released a minty-lemon fragrance and attracted White Peacock butterflies. Frosty-colored Liatris seed heads released tufts of white as I brushed by, and the odd apple snail shell caught my attention. With the sound of the wind as a companion, I had a delightful hour’s hike to the dome. A line of Slash Pines, perhaps only inches higher in elevation gradually closed in from the west at my destination leaving only a narrow gap for the track to continue onwards.

As if on cue a ray of sunshine pierced the clouds transforming the grey leafless dome momentarily to gold. With the Sun appeared several Halloween Pennant dragonflies and a Scarlet Skimmer. I stopped to take a photograph and despite the shallow depth of the mud, my boots began to stick, pulling out with a distinct pop as I left the track to approach the dome. My cypress stand was some 80 yards in diameter. Classically lower trees encircled it and each succeeding concentric ring rose slightly higher creating a perfect dome shape with the tallest trees towards the center perhaps as high 70 feet and certainly besting the tallest pines nearby.

To the uninitiated cypress domes are counter intuitive. They appear from a distance almost as little hillocks but are in fact water-filled depressions, at least in the wet season, which brings us back to opposites and prairie hammocks. Those tree islands typically develop on limestone outcrops that raise them slightly above the surrounding terrain. Cypress domes, however, form in slight depressions created when weaker areas of limestone bedrock subside or dissolve from the action of the acidic by-products of rotting plant material. One might think the taller trees in the middle represent greater age, but the difference in height may be down to increased growth vigor instead.

Photo by Rose Flynn

Imagine a newly formed depression on the prairie. The initial trees that colonize the beginnings of that ephemeral pond will have no better soil conditions than our hat-rack cypress. So an outer ring of stunted trees develops. Over time they drop their needles into the pond creating slightly better soil conditions for the next ring of trees which grow slightly taller, and so on and so on. Each successive ring also has a slightly longer hydroperiod because they are further into the bowl. So the tallest trees may not necessarily be the oldest trees, rather they have just experienced the best growing conditions. And to confound the model, were we able to count the tree rings of outer individuals, they might not be older because the outer trees also experience the highest mortality due to a shorter hydroperiod and greater susceptibility to fire.

Cypress trees, like all aquatic organisms, face certain challenges from being periodically inundated. Water is an excellent solvent, able to readily transport most chemicals required for life, but it’s also about 10,000 times more viscous than air, meaning that life supporting gases, primarily oxygen and carbon dioxide move very slowly in their dissolved state, requiring special adaptations. Water lilies for example have hollow stalks so that oxygen can be channelled to roots buried in anaerobic muck. On the outer fringes and into the dome’s interior I encountered cypress knees; those knobby conical structures that have proved such a mystery to scientists.

All sorts of sophisticated experiments have been conducted over the past 80 years, even hermetically sealing them in transparent cases with hoses connected to all sorts of instruments, but the results are inconclusive or contradictory. However, most likely they are involved in some sort of gas exchange as they typically grow to an average height just above the local site’s mean high water level, and they also provide some sort of anchoring mechanism as they typically appear where the root system takes a distinct downward turn, perhaps here in South Florida exploiting a small solution hole. We also know they store starch.

Although the dome was dominated by cypress there was a struggling understorey kept in check by the cypress canopy’s shade. It comprised pond apple, Dahoon holly, pop ash, a few Carolina willow and some cabbage palms near the outside; all species that create a succession canopy in swamps if there is a perturbance like logging or fire. This one sheltered some sparse sawgrass too.

The cypress trunks had characteristic buttressed bases. These swellings help them absorb oxygen and provide stability in high winds. I could detect the normal high water level from the line where the patches of lichens ended. The closely spaced trunks serve to dampen air movement and trap moisture under the canopy, so that higher up, the cypress branches were festooned with bromeliads.

Cypress cones. Photo by Rose Flynn

Waxy cones and pendulous catkins hung on many of the cypress and the typically clear water below was instead dusted with their pollen. Each cone typically contains 16 seeds that  look a bit like dried-up petals the size of a finger nail. Squirrels often messily tear apart ripe cones and in the process drop seeds. In the not so distant past noisy flocks of now extinct Carolina Parakeets would have also performed this service. The seeds then need a complex sequence of conditions to successfully germinate. Ideally they will fall into water where they can soak for several months to soften their tough outer husks, but they can’t germinate there and must ultimately settle on exposed, but moist soil. This is why cypress trees need alternating wet and dry.

The seedling then must quickly thrust upwards to avoid being submerged when the rainy season returns or they’ll drown. Once mature however, they can survive both periodic flooding and drought. Because of this, if there’s permanent water in the center of the dome, there will be what looks like a donut hole from the air, devoid of cypress.

My dome was true to form and sure enough as I sloshed inward I encountered a small flag pond open to the sky. The alligator flag indicated even deeper water. Had I been a truly dedicated scientist I would have waded into the center to measure the depth, but in the dry season these frequently become gator holes, and as I was alone and had the excuse of inappropriate boots, I opted just to admire the pond then head home. My hike back was much quicker as I decided to bypass the rutted track altogether and found it much faster striding over the firm prairie in just a few inches of water. It helps to have long legs though!