November 27, 2006
This week I decided to wander a couple of days in the mangroves and scrub. My friend Ismael drove me to the biosphere reserve's wildlife-viewing tower at Petén Tucha where I'd begin my hike. As we approached the tower we heard a squeal which Ismael instantly recognized as that of a White-tailed Hawk. This is a tropical species distributed from the US border to Argentina, specializing in open savannas and scrub.
Once we'd climbed the tower and had a view over the forest canopy we saw who was squealing. The White-tail had a fledgling lounging in a treetop and when the parent came near carrying food the young one would beg. It looked as if the parent were trying to entice the kid to fly out and try hunting itself but the kid seemed to prefer having its food brought to it.
The parent teased the fledgling awhile, then fed it, then began circling the nest area. While the parent was circling a Turkey Vulture wandered into the vicinity and to my surprise the adult White-tail began dive bombing it. The hawk attacked several times until the vulture sailed away.
"Why on Earth would a hawk be so hard on a poor old vulture?" I asked Ismael. To me it was just one of those many questions I scratch my head over every day, then move on. But, Ismael, knowing the local birds better and maybe having a sharper eye than I, kept quiet as he binoculared the bird and then finally said:
"No es un zapilote" -- "That's not a vulture."
I was taken aback. Of course it was a vulture, a Turkey Vulture with slender wings tilted in a V, a long, thin tail, a black bird with primaries and tail a little silvery... A common Turkey Vulture like those I've known since I was a kid watching them circling over our soybean fields in Kentucky!
"Look at the legs," he said. "They're orange... "
It was true. Moreover, now that I studied the bird more closely, something just didn't seem right.
Ismael was confused, too. He knew about a vulture- mimicking hawk here, the Zone-tailed Hawk, but that bird definitely has white feathers, while this one looked all-black. However, after we'd gone through all the possible species again and again we decided it had to be a Zone-tailed Hawk. For some reason we just weren't seeing the white feathers. Maybe it was the light. Also, my field guide said "...white tail bands of the adult are often partly concealed... " The book went on to say that sometimes Zone-tailed Hawks soar with Turkey Vulture flocks, further enhancing their deception. Zone-tails occur in a variety of arid and semi-arid habitats, wooded to semiopen, from the US border to southern Brazil.
So, the White-tailed Hawk had seen through the Zone- tailed Hawk's deception, even though I was so easily fooled. Moreover, now I know why the White-tailed drove off the Zone-tailed. My field guide says that Zone- taileds eat small mammals, reptiles, and BIRDS. The White-tailed parent hadn't wanted the Zone-tail to eat the squealing fledgling in the tree below.
You can see a White-tailed Hawk at http://www.mangoverde.com/wbg/picpages/pic30-182-5.html.
A Zone-tailed Hawk looking a little like a vulture is at http://www.schmoker.org/BirdPics/Photos/Raptors/ZTHA12.jpg.
TURTLE IN A FRESHWATER SPRING
That wildlife-viewing tower at Petén Tucha is quite something. It's built of rough poles and it stands beside an acre-size freshwater spring surrounded by saltwater mangroves. During my first night out I erected my tent on the top level, the tent being needed for mosquitoes despite the wind being so gusty that the tower swayed constantly. In the end, I stayed at the tower for 24 hours. Not a single other person visited there. You can see a picture from the top level overlooking the spring at http://www.backyardnature.net/n/06/061127o.jpg.
That picture shows how blue the water is. You don't realize how clear it is until you see bubbles coming up from below, and then you watch them rise for so long that you know that they must have become visible many feet below the water's surface.
I also realized the water's clearness when a turtle swam right below me as I sat with my legs dangling over the top level's floor. Since there are no real rivers in the northern Yucatan, turtles are more uncommon here than you might expect, so I was tickled to be getting such a good view of one. I figured that in this remarkable ecosystem -- a freshwater spring surrounded by saltwater mangroves -- it would surely be an exotic species.
But as soon as that turtle poked his head out of the water I saw it: A conspicuous yellow stripe all along the head and neck, with a dingy red stripe above the eye. I'd seen this turtle before, and I've talked about it in this Newsletter. In March of 2002 I reported on eight of them sunning in a springy pond in Mississippi and in October of 2005 I told about one crossing Fred's driveway in California's Sierra Nevadas. It was a Red-eared Turtle, which I've said before is distributed from southern Michigan and New Mexico south to South America, plus there are introduced populations in Europe, Israel, South Africa and other places. This is the main "pet shop turtle," the turtle that has starved and dried up in a million kids' neglected fishbowls. You can see the picture I took of that one at Fred's last year, looking just about exactly like what I saw here, at http://www.backyardnature.net/pix/r-e-turt.jpg.
Red-eared Turtles -- called Mesoamerican Sliders by my reptile book for this area -- are a freshwater species, so it's a mystery to me how this turtle got here across the enormous acreage of saltwater mangrove surrounding us.
My book says that Red-ears in this area are preyed upon by Morelet's Crocodiles. I saw at least one Morelet's in Petén Tucha and signs of more. I don't know whether Petén Tucha's clear water will mainly help the crocodile stalk the turtle, or help the Red-ear watch for the croc.
PETÉNS & MARSHES
The word "petén" in Petén Tucha describes an important component of this area's wetland ecosystem. A petén is a low rising or hammock, usually round to oval shaped, emerging from the wet marsh. You can see one of the marshes I hiked across this week at http://www.backyardnature.net/yucatan/marsh.jpg.
No peténs appear in that picture but if they did they'd show up as no more than a clump of trees surrounded by flat marsh. The important thing about peténs is that they contribute enormously to a marsh's biodiversity.
In fact, a petén is typically surrounded by concentric rings of biological zones, each ring harboring plants and animals adapted to a particular water depth or elevation above high tide. At the heart of the petén ecosystem stand trees such as palms, strangler figs, Poisontrees (Metopium), Chicle Trees and frangipani (Plumeria). Next to the water Logwood trees appear. Eventually trees give way to grasses, cattails and the like, and then to submerged vegetation.
Often larger mammals take refuge among a petén's trees and birds often roost and nest there. A petén is an ecological island.
Those of you familiar with Guatemala may know that northern Guatemala is referred to as The Petén. That's because most of northern Guatemala is fairly flat, seasonally flooded, and during the rainy season there are lots of island-peténs there.
Hiking out of Petén Tucha, as I passed through a tunnel cut through the mangrove suddenly I was surprised by a loud whistle-like shriek that trailed off into a series of mammalian HOO-HOO-HOO-HOOs. I looked in vain for the hoo-er but the vegetation was as dense as a mangrove swamp can be.
My local naturalist friends and I agree that I probably had heard a Spider Monkey, ATELES GEOFFROY. There's no reason why I shouldn't have heard one since they are known to hang out around Petén Tucha, plus there just are no other animals here that go around HOO-HOO-HOO-HOOing. About 60 air-miles southwest of here a number of Maya families at Punta Laguna escort paying visitors to see their resident Spider Monkeys. Spider Monkeys used to be much more common here than now but they've suffered greatly from habitat destruction, being captured for the pet trade, and being hunted for food. You can see several pictures of one at http://animaldiversity.ummz.umich.edu/site/accounts/pictures/Ateles_geoffroyi.html.
Originally we had two monkey species in the Yucatan, the other being the Howler Monkey, Alouata palliata. Now the Howlers seem to be extirpated from the northern region. Farther south in Guatemala's Petén region and in the Mexican state of Chiapas I've often seen them and frequently heard them roar majestically and blood- curdlingly like lions.
Spider Monkeys appear to be more tolerant to habitat disruption than Howlers, and the Spiders don't call attention to themselves by roaring. Still, as with the howlers, the species is regarded as threatened with extinction.
A HORSESHOE CRAB'S UNDERSIDE
Usually the horseshoe crabs I find washed up on beaches are shattered, incomplete wrecks of the former organism. However the other day I came upon a very recently dead one in good shape, so I studied his parts closely, and photographed him. You can see that picture at http://www.backyardnature.net/yucatan/hs_crab.jpg.
In the picture I'm holding onto the crab by one of its 12 appendages. The ten large ones, called pedipalps, are for walking but the two small ones at the top, called chelicerae, are used for manipulating food into the mouth. Notice that the lowest, largest pair of legs each end in brush-like structures. These are used for stirring up and pushing aside sediment when the crab burrows into the seafloor.
In the creature's center, at the base of the leg I'm holding, you can make out a hole. That's the mouth. If you look closely you can see that the base of each leg arising around the mouth is equipped with small, brown spines called gnathobases pointing downward toward the mouth. These keep food from moving in any direction other than toward the mouth. As food works toward the mouth the spiny leg bases grind it. It's all a very simple system for a simple, primitive organism.
The five pairs of wafer-like items covering the shell's bottom half are gills. You can't see them in the picture but from each gill arise about 150 leaf-like membranes called lamellae. The moving gills keep oxygen-rich water flowing over the lamellae, which absorb the oxygen. The gills also function as paddles for propelling juvenile horseshoe crabs through the water.
Background info on horseshoe crabs, which are actually "living fossils" closely related to extinct trilobites, is at http://www.backyardnature.net/yucatan/hs_crab.htm.
RED MANGROVE'S SELF-ROOTING FRUITS
Of the four mangrove tree species constituting the mangroves here, Red Mangrove is the most eye-catching. It's the one with gangling "stilt-roots," as shown at http://www.backyardnature.net/yucatan/mangred.jpg.
Red Mangrove inhabits the deepest water of the four species, and its fruits are the most curious-looking. You can see a fruit photographed during my hiking trip at http://www.backyardnature.net/yucatan/mangrove.jpg.
That picture shows two Red Mangrove flowers with fruits developing from the ovaries in the flowers' centers. The fruit on the right is much more developed, as indicated by the fact that inside it a seed has already germinated and now a very sizable root (technically the radicle, since it's the seed embryo's first "root") is emerging from the fruit, pointing downward.
The dangling "root" is about eight inches long. Sometimes when the fruit falls from its flower the "root" stabs into the mud, thus planting a new Red Mangrove right beneath the parent tree. More typically, however, the fruit with its "root" falls into water and floats away. When the "root" makes contact with mud it grows into it and then the tree develops as you'd expect. Still, it's fun to know that a Red Mangrove fruit, at least under certain conditions, can actually plant itself.
Mother Nature almost always prefers for offspring to settle farther away from the parent so that parent and offspring don't end up competing for the same resources. Red Mangrove may constitute an exception, however, since one of Red Mangrove's traits is that they often grow so closely together that their stilt roots interlock, forming impenetrable thickets that are the delight of shelter-seeking wildlife. Also, they catch soil particles that otherwise would wash away, building up the land. You can see a view through a maze of Red Mangrove stilt-roots at http://www.backyardnature.net/yucatan/mangmess.jpg.
Most of my hike back to town took place in cattle-chewed, cactus-rich scrub. On my second night out I camped next to a plant some potted-plant-loving North Americans might find vaguely familiar. You can see if the plant's appearance rings a bell with you by going to http://www.backyardnature.net/yucatan/beaucarn.jpg.
Local Mexicans call it Palmilla, saying it's a kind of palm, but if you look closely you'll see that it's very unpalmlike. For one thing, it's stem branches, and palm trunks rarely branch. For another, the leaves are neither palmately nor pinnately compound, like the vast majority of palms, but rather are long and slender like a sword's blade. Some of these plants are fruiting now and if you could see the fruit you'd see that it's not at all like a typical palm fruit -- like a small coconut -- but rather it's a dry, lightweight capsule.
In fact, this palmlike tree is a member of the Lily Family, not the Palm. In North America small potted specimens with gray trunks expanding enormously at their bases, and topped with topknots of arching, slender, green blades are sold under the trade names of Mexican Ponytail, Ponytail Palm, Bottle Palm, Elephant's Foot and other names as well. The species sold in pots is usually Beaucarnea recurvata. I think that ours is BEAUCARNEA PLIABILIS, because I've seen that species listed for the Yucatan. It's also listed as a threatened species. A page showing a potted Beaucarnea and describing its care is at http://www.plant-care.com/1602-ponytail-palm.html.
Our Beaucarnea pliabilis rises above the surrounding low, thorny scrub rather majestically, lending the landscape an extra touch of exotic feeling. In the picture you can see its swollen trunk-base, explaining one of it's names, "Elephant's Foot." This swollen trunk serves as a water- storage structure. Overwatered, store-bought potted specimens often possess grotesquely large, spherical boles with teeny, green topknots.
On the night I pitched my tent next to the Beaucarnea in the picture the wind roared across the scrub from dusk to dawn. Several times in profound darkness I awakened and just listened to the wind streaming through the tree's jutting-out branches and causing its stiff blades to flap and clack against one another. It was a homey feeling lying beside such a distinguished being, knowing its roots ran beneath where I lay on the ground.
In the morning an endemic Yucatan Wren came with its husky krrohrrrrr complaint glaring at my tent as he hung onto the Beaucarnea the way you expect a wren to do, even an endemic one.
"Krrohrrrrr yourself," I replied similarly huskily, feeling just splendid, with a full night of wind-roar and Beaucarnea-flapping and -clacking energy churning around inside me.
CHRISTMAS BOOKS FROM AMAZON.COM
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EGRETS, HERONS & IBISES
Out in the mangroves it's normal to see mixed flocks feeding together in areas of open water 2-4 inches deep. A normal flock of about 20 birds may be half Snowy Egrets, 1/3 White Ibises, with a sprinkling of Tri- colored Herons, Little Blue Herons, Great Egrets and maybe a Willet or two. Feeding in a group like this seems to scare up more fish for everyone, plus there are more eyes to scan for enemies.
After you watch such a flock awhile you see that each species has its own strategy and personality. Often the flock I've been watching more or less follows the White Ibises who systematically probe the mud with their long, curved beaks, more interested in worms and other mud dwellers than fish. Snowy Egrets appear to follow the ibises stabbing at fish the ibises scare up, frequently getting into noisy fights with one another, and sometimes trying to rob an ibis of its catch. The other heron and egret species stay on the fringes and are less engaged with the group.
Then a Common Black Hawk comes YEEP YEEP YEEPing, lands on a snag amidst the mixed flock and everyone flies away, the ibises looking over their shoulders in absolute disgust.
In other words, such a flock of birds shows structural elements similar to that of a typical human society. Most people I know resemble the no-nonsense, work-a-day, nose- in-the-mud ibises, or else the boisterous, redneck Snowy Egrets, or the timid little Willet or maybe the philosophical outsider, the hesitant Little Blue Heron, and then there's always the loud, obnoxious one who rampages into town upsetting everyone by insisting on having things his own way, like the Common Black Hawk.
However, one great difference between a flock of birds and human society is that a White Ibis is stuck with his living strategy for his whole life, while a human can change. A human has the potential to learn from mistakes and to consciously change his or her assumptions about life as more and more information and experience is acquired, and to change his or her behavior accordingly.
Yet, it seems to me that most people don't like to change at all. They may talk about wanting to change but what they really want is to keep securely to their daily routines, to not rock the boat and not take chances, not be different from everyone else, just behave acceptably and do what's expected of them. This, even when it's clear that our society's distinguishing living strategy -- that of being consumption-based and depending on continual growth -- is unsustainable, and threatens Life on Earth.
So, there I am sitting in the mangroves watching egrets, herons and ibises, wondering what will happen to all the exquisitely adapted plants and animals around me as global warming manifests itself, pollution keeps getting worse, as more and more people cut more and more firewood from the surrounding scrub, and overfishing continues until basically the sea around us is fished-out. What will happen as these long established -- one could say traditional -- unsustainable behaviors continue, as most humans choose to keep doing what they've always done?
And I just wonder: Where did the loony idea come from that somehow it's more family-oriented and God-fearing to behave traditionally and unquestioningly of commonly accepted values -- to reject the Creator's gift to humans of being able to think and to change? Why do most people choose to live the lives they were born into, exactly as egrets, herons and ibises?
Best wishes to all Newsletter subscribers,
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