JIM CONRAD'S
NATURALIST NEWSLETTER
Issued in Río Lagartos, on the northern coast of
Yucatán, MÉXICO
in Ría Lagartos Biosphere Reserve

March 29, 2015

THE GREAT BLUE HERON'S "WHITE MORPH"
This week Paco and I were on a flamingo viewing tour with a group from British Columbia and Nebraska when a large, all-white heron turned up foraging near a mud bar. The bird was clearly larger than the commonly encountered Great Egret, Ardea alba, plus its beak was dark but yellow-tipped -- the Great Egret's is all yellow -- but we couldn't see the legs, since they were submerged, and we needed to see them for an identification. Slowly we approached, the idea being to snap a picture when the heron flew, revealing his legs. The strategy paid off, as you can see at http://www.backyardnature.net/n/15/150329mf.jpg.

This bird's legs are dark, but yellow at the top, and with yellowish feet. The bird in the picture landed on the mud bar, offering an even better view of the beak and legs, shown at http://www.backyardnature.net/n/15/150329mg.jpg.

Here was something different, and interesting. For, in field guides for American birds, in descriptions of the common but spectacular Great Blue Heron, usually there's mention of a bird that looks and behaves exactly like the Great Blue Heron, except that it's white. And this is what Paco and I were seeing. My dogeared old Birds of North America by Robbins, copyright 1966, calls it the Great White Heron, Ardea occidentalis, and says that it's "very closely related to Great Blue Heron." It's illustrated as a bird with a brightly yellow beak and legs, and described as occurring in southern Florida and the Florida Keys.

But, a few years after the Robbins guide was published, new field guides came out interpreting the Great White Heron as something else. I lined through the names in my Robbins and wrote "Great Blue morph, Ardea herodias." The name Ardea herodias is the same used for the common Great Blue Heron. In other words, a few years after the Robbins book, experts decided that the big, all-white heron was not a separate species, but rather just a color phase of the common Great Blue Heron -- a "morph."

Bird morphs are not geographical races or seasonal forms. To be a morph, individuals displaying the distinct color phase must occupy the same habitat at the same time as the more broadly recognized species of which it's considered a morph. Morphs don't need to occupy the entire area of distribution of the species -- as shown by Robbins describing the Great White Heron's white morph as only found in southern Florida. Also, morph individuals need to occur within a species more frequently than do random mutations. White morphs such as the Great Blue's are not albinos, which are birds whose pigments didn't develop properly because of a randomly occurring genetic malfunction. Amazingly, even still, scientists aren't sure whether the quality of being a morph is inherited. At this time, the Great Blue Heron's Wikipedia page lists the "white morph" as a subspecies of the Great Blue, whose scientific name is Ardea herodias ssp occidentalis.

However, it isn't that simple. The Sibley Guide to Birds, published in 2000, has been the authority for a generation of North American birders. In 2010, David Sibley, the guide's author, publicly announced that, with regard to the white morph of the Great Blue Heron, "... the more I learn the less clear-cut this seems, although I still think it’s at least a good subspecies." His well documented statement of doubt is nicely presented here

On that page, Sibley states that Great Blue morphs "... are also said to occur in Cuba, Jamaica, the Yucatan, and off Venezuela but are apparently smaller than the Keys birds and scarce (not a majority). What do these birds actually look like and what is their status?"

So, here we have more information about what Great Blue Heron morphs look like, and what their status is. Diego had told us that in Ría Lagartos Estuary about six Great Blue morphs are known to exist. Our bird's dark legs with yellowness at the extremities, and the dark bill flushed with yellow, match those of others pictured on the Internet. Diego agrees that our picture show a Great Blue Heron white morph.

*****

FRANKLIN'S GULLS
During the winter our most abundant gull here, by a long shot, is the Laughing Gull, which during early winter is a nondescript, dark-backed gull with a dingy head. Nowadays as spring approaches, the heads of more and more Laughing Gulls are abandoning their winter plumage and developing conspicuous, handsome, black "hoods."

This week gulls turned up displaying the same basic plumages as Laughing Gulls, but something about them was different. Some are shown at http://www.backyardnature.net/n/15/150329fg.jpg.

They're Franklin's Gulls, recognizable as such by the white spots near the tips of their wings. They're migrating north to their nesting grounds in south-central Canada and the north-central US, and are found here only during migrations. They're the common gull of the American prairies, and they've just overwintered along the Pacific coast of South America. In North America normally you don't have to worry about confusing Franklin's Gulls with Laughing Gulls because Franklin's Gulls occur in mid-continent, while Laughing Gulls are coastal.

It's a little surprising to see so many Franklin's Gulls here, for their main migratory route is along southern Mexico's Pacific coast, then northward through central and eastern Mexico. However, they're known to be rare winter visitors here along the Yucatan Peninsula's northern coast. Diego says that this year we're seeing an unusually high number of them.

Anyway, this is more proof that spring really is coming.

*****

LADDER-BACKED WOODPECKER, NORTHERN YUCATAN SUBSPECIES
Up in Texas, Ladder-backed Woodpeckers commonly showed up cavorting among the Texas Liveoaks at the community park along the little Dry Frio River. You can see how the birds looked there at http://www.backyardnature.net/n/b/picoides.htm.

Here we have the same species, but a different subspecies. Nine subspecies of Ladder-backed Woodpecker, Picoides scalaris, are recognized. Apparently ours our subspecies PARVUS, described at the Avibase.bsc-eoc.Org website as occurring in the northern Yucatan Peninsula, including Cozumel and Holbox Islands.

Our Yucatan birds strike me as having more extensive black markings on their heads and tanner underparts than the Texas birds. You can see one of our parvus birds seen this week at http://www.backyardnature.net/n/15/150329wp.jpg.

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CHANK EGG CASES
By now we've learned that seashell-producing, gastropod-type mollusks sometimes produce egg cases looking like papery wafers strung together in a line. We look at those of the Pear Whelk at http://www.backyardnature.net/n/14/141228bu.jpg.

Those of the Knobbed Whelk are at http://www.backyardnature.net/n/11/110515wk.jpg.

And of the Lightning Whelk at http://www.backyardnature.net/n/15/150222wl.jpg.

And the more ornate ones of the True Tulip at http://www.backyardnature.net/n/14/141214tu.jpg.

Despite such familiarity, the object that washed up this week on the Gulf of Mexico sand was so large and regularly formed that I doubted they were just another mollusk species' egg cases. You can see this new discovery at http://www.backyardnature.net/n/15/150329ck.jpg.

The wafer-like items were attached along one side to a woody-looking, splinter-like thing, as shown at http://www.backyardnature.net/n/15/150329cl.jpg.

Despite the size, the thing turned out to be yet another kind of strung-together egg cases of a seashell-producing, gastropod-type mollusk, this time that of the West Indian Chank, TURBINELLA ANGULATA. West Indian Chanks occur from the US's Florida Keys south through the Gulf of Mexico and the Caribbean to northern South America. Our egg cases are so large because West Indian Chanks can grow over a foot long (36cm).

West Indian Chanks live on a variety of subtidal and offshore mud, rock or sand beds, and mangrove lagoons vegetated with seagrass.

They're called chanks instead of whelks or tulips because they belong to a different mollusk family, the Turbinellidae, than the whelks' Buccinidae, or the tulips' Fasciolariidae.

The interesting name "chank" is a corruption of the name "shankha," which is applied to the Divine Conch or Sacred Conch, Turbinella pyrum, a closely related species from the Indian Ocean. Sometimes the word "chank" is used interchangeably with "conch," but that's sloppy talking.

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ATLANTIC BUBBLE SHELL
Across the estuary from Río Lagartos, at low tide on the wet, sandy beach on the Gulf of Mexico, you can pick up lots of shiny, brown-speckled, inch-long (27mm) snail-like gastropod shells like those shown at http://www.backyardnature.net/n/15/150329bb.jpg.

The shells aren't formed into conspicuous whorls the way we think of snail shells as being, but they whorl a little, as you can see in a close-up of a shell's "closed end" shown at http://www.backyardnature.net/n/15/150329ba.jpg.

Volunteer identifier Bea in Ontario with her new Peterson sea-shell field-guide didn't have much trouble pegging these shells as Common Atlantic Bubbles, BULLA STRIATA. Atlantic Bubble shells commonly turn up on warmer Atlantic beaches from Portugal and the Mediterranean south to the western coast of Africa, to Florida in the US, the Caribbean and Gulf of Mexico, south to northern South America.

Though most bubble-shell species -- members of the genus Bulla -- graze algae in seagrass beds, the Common Atlantic Bubble is thought to be predatory on other mollusks. It burrows in loose sand and mud in estuarine flats and seagrass beds.

*****

GYMNOPODIUM FRUITING
We've run into Gymnopodium floribundum before, a much-branched shrub or small tree distributed from southern Mexico south to Honduras. When we profiled the plant earlier, it was abundantly flowering -- in accordance with its species name, floribundum. In February, its flowers issued a "...penetratingly sweet fragrance, like honey, but almost too much of it." You can see the curiously green, much simplified but elegant blossoms on our page at http://www.backyardnature.net/yucatan/gymnopod.htm.

Now later in the dry season, our local, dry-season leafless Gymnopodium floribundum trees are producing abundant fruiting clusters that in early morning sunlight cause the whole tree to seem to glow as if it had an interior fire. Its interesting, fingernail-size, three-winged fruiting clusters are shown at http://www.backyardnature.net/n/15/150329gz.jpg.

If you're familiar with the edible herb called dock, or the pretty vine called Coralvine -- both members of the Buckwheat Family, the Polygonaceae -- you'll notice similarities between those plants' fruiting heads and the ones on our little tree. That's because Gymnopodium floribundum also belongs to the Buckwheat Family.

Therefore, as with the fruiting heads of dock and Coralvine, each three-winged fruiting head of Gymnopodium floribundum consists of three one-seeded, achene-type fruits bearing a papery wing, which helps disperse the fruit on the wind.

Despite this being such a handsome plant, it simply doesn't seem to have a common name. Of course the Maya know it, calling it ts'iits'ilche' or sak ts'iits'il che'. For us Northerners, the name Gymnopodium probably is easier.

The Maya credit the tree as a good source of nectar for their honeybees, and as worthy of being cut for firewood.

*****

RED-FLOWERED COASTAL PRICKLY-PEAR
On a birding tour in the savanna/ranchland zone we were passing by a big patch of sprawling prickly-pear cactus that I've always assumed to be Coastal Prickly-pears, Opuntia stricta. We've profiled that species at http://www.backyardnature.net/mexnat/opuntia1.htm.

On that page you can see that Coastal Prickly-pears produce yellow flowers. However, the blossoms on the cacti found this week were vividly red, as shown at http://www.backyardnature.net/n/15/150329op.jpg.

Still, a peep into the blossom's throat showed that the five stigma lobes were pale yellow, just like the Coastal Prickly-pear's, as shown at http://www.backyardnature.net/n/15/150329oq.jpg.

Moreover, each spine cluster of this week's cactus was fringed on one side with many tiny, slender "glochids," and produced several much longer, yellowish, slightly curved spines turning brown as they age, exactly as with the Coastal Prickly-pear, as shown at http://www.backyardnature.net/n/15/150329or.jpg.

The plants sprawled across the ground without forming a tree-like trunk, as seen at http://www.backyardnature.net/n/15/150329os.jpg.

In other words, this seemed like a normal Coastal Prickly-pear, except that it was producing red flowers instead of yellow. On the Internet, the Flora of North America, Wikipedia, the UN's FAO, and the Florida Native Plant Society all say that the Coastal Prickly-pear's flowers are yellow. However, CICY, the Yucatan's central institution for science, shows both yellow and red flowers for the species.

Therefore, since CICY's experts seem to be pretty good, and our red-flowered plants seem to be Coastal Prickly-pears in every respect except flower color, I'm going along with CICY: Coastal Prickly-pear can have either yellow or red flowers, at least here along the Yucatan's northern coast.

*****

HALITE/ ROCK SALT AT THE SALT PONDS
Ron from Colorado wanted to see the salt ponds at Las Coloradas. When we got there he was as impressed as anyone by the huge network of interlocking ponds, the algae-pink waters, the wild feeling of the absolutely flat, wind-scoured landscape, and by the remarkable heaps and mounds of snowy foam, or biofoam. Recently we looked at a pink-water pond and part of the salt-making factory at http://www.backyardnature.net/n/15/150315pk.jpg.

We've examined the phenomenon of the biofoam at http://www.backyardnature.net/yucatan/sea_foam.htm.

I told Ron that sometimes you could find conglomerations of salt crystals. Ron was interested in this, so we went looking. You can see salt crystals at a pond's edge at http://www.backyardnature.net/n/15/150329s_.jpg.

It was easy to pick up egg-sized chunks of fused salt crystals, as shown at http://www.backyardnature.net/n/15/150329sa.jpg.

Even without a magnifying lens you could see that this was salt, because the crystals composing it formed little cubes. If you'd crush this cluster the right way, you'd end up with tiny grains of table salt, each grain being a cube with six equal faces, and all the cube's edges uniting at 90° angles. If the crystals had formed rhombohedrons, with some angles being larger than 90° and others less, we'd probably have crystals of the mineral called calcite. A closer look at the above cluster better shows the crystals' cubical nature at http://www.backyardnature.net/n/15/150329sb.jpg.

Some of those crystalline units look more like long boxes than cubes, and the crystals aren't neatly aligned as they would be if all were perfectly cubical. That's because crystals habitually grow together, angles and faces can be distorted by impurities, and parts can be eroded away, destroying the crystal's symmetry. Crystal form is defined by the configuration of atoms in the crystal's molecule. Atoms of calcite gather themselves into patterns forming rhombohedrons, while atoms of salt bond with another at right angles, resulting into cube shapes.

Not only did we find small coagulations of crystals, but also slabs of salt such as what's shown in my hand at http://www.backyardnature.net/n/15/150329sc.jpg.

That was picked up from atop muddy sand at a salt pond's edge where wind-deposited mounds of foam evaporate. The object consists of salt mixed with impurities such as the sand it formed atop, and organic matter in the foam. It was hard to find cubical crystals in it because impurities disrupted crystal growth. Still, if we could have ground up this object into tiny enough particles and looked at them under a microscope, they'd have been perfectly formed cubicle crystals.

Years ago someone pounded a wooden pole into the salt pond and a similar mass of impure salt formed around it. You can see the remains of that pole, with its naked end pointing toward the picture's top, right corner, at http://www.backyardnature.net/n/15/150329sd.jpg.

When salt crystals form such rock-like masses, the masses are referred to as rock salt. If the rock salt is pure enough to be thought of as a mineral with a chemical formula, we can call it halite, and write its chemical formula as NaCl -- which is sodium chloride, or salt.

*****

MUD WEED, OUR MOST CONSPICUOUS ALGA
During this half year at Río Lagartos I've spent a lot of time identifying plants and animals. Imagine my frustration that during that time I've been unable to name one of the most dominant and conspicuous of all organisms occurring here. To get a feeling for the enormity of this failure, take a look at the aerial photograph of the western side of Ría Lagartos Estuary shown at http://www.backyardnature.net/n/15/150329ag.jpg.

In that image, the blue Gulf of Mexico occupies the top, left corner. A slender finger of land separates the Gulf from the estuary that parallels the Gulf just inland. Río Lagartos is the white, pyramid-like presence near the picture's top, right corner, projecting into the estuary. The similar, upside-down-pyramid at the lower left is San Felipe, and connecting the two towns at the picture's bottom is the coastal road I bike on days I don't have tours.

The dark-banded expanse of estuary between Río Lagartos and San Felipe is what concerns us here, for that are of dark bands coincides with submerged beds of almost pure stands of a felt-like, ropy and often lobed alga. You can see the alga as it appears in clear water when looking over the side of a boat -- its green, paddle-shaped lobes heavily coated with natural, calcium-carbonate-rich marl -- at http://www.backyardnature.net/n/15/150329ah.jpg.

In this area it's easy enough to reach over the boat's side and pull up irregularly formed lobes and stringy strands of the alga, as shown at http://www.backyardnature.net/n/15/150329ai.jpg.

Another shot, showing flat pads budding from thick, cylindrical strands that behave like rhizomes creeping through the mud is shown at http://www.backyardnature.net/n/15/150329al.jpg.

Under certain conditions, the pads "bud," into interesting formations, as seen at http://www.backyardnature.net/n/15/150329ak.jpg.

The alga feels like wet felt, and when the pads are pulled apart you see that the pads and cords are all composed of what appear to be tiny, green filaments, though they're branched as shown at http://www.backyardnature.net/n/15/150329aj.jpg.

We've identified several alga species here whose complex-looking bodies proved to be composed of such networks of tiny, branching tubes, with the tubes themselves lacking cell walls, so that cell nuclei, chloroplasts and other organelles migrated throughout them in such a way that the whole, large body was considered just one cell. Such organisms with free-roaming nuclei and organelles are known as "cenocytes." And now I know that our mystry alga is cenocytic, too, for finally I found someone who could simply tell me what the alga is.

My biologist friend Willie told me about Dr. Ileana Ortegón-Aznar, head of the department of Tropical Marine Resources at UADY, the Autonomous University of the Yucatán. Dr. Ortegón-Aznar identified our alga as a species of the genus AVRANILLEA. Species of Avranillea belong to the alga order Caulerpales, in which algal bodies are composed of filaments that somehow, mysteriously, organize themselves into much larger bodies that behave like leaves, stems and roots of flowering plants -- just as our Avranillea does.

Dr. Ortegón-Aznar says that Avranillea is common in this area, and that although it often grows in areas of high nutrient content and/or much organic matter, its presence here is not necessarily an indication of polluted water.

However, I hypothesize that the vast area of Ría Lagartos Estuary so totally dominated by Avranillea got that way because about forty years, right across from Río Lagartos, a canal was cut through the slender finger of land separating the Gulf from the estuary. I bet that the canal caused the area currently occupied by Avranillea to lose its ability to "flush" with changing tides. Now very much of the estuary's tidewater streams through the canal, leaving relatively "dead water" covering our Avranillea prairie.

Despite the dominance of Avranillea in this dead-water area, this part of the estuary is not an ecological desert. Diego says he sees lots of creatures there, including many Tarpon, which wouldn't be there if they didn't have something to eat. The canal may have drastically altered the population structure of that part of the estuary, but it didn't kill it.

Still, I find mention of an invasive Avranillea species taking over certain areas of shallow water in Hawaii, with such drastic effect on local species diversity that efforts are made to physically remove it. Also, nowadays another member of the order to which Avranillea is assigned, Caulerpa taxifolia, is invading much of the Mediterranean with negative effects on biodiversity. Therefore, our Avranillea has relatives who can be mean and aggressive, so it's not beyond question that our local Avranillea may be doing nasty things, too. But, all this is just conjecture.

In Hawaii where an Avranillea species is causing trouble, folks sometimes refer to their invasive species as Mud Weed. I think that that's a good name for it, since here our Avranillea grows in mud, and normally is so heavily coated with carbonaceous marl that one wonders how it survives.

*****

NATURAL OILY SHEEN ON WATER
Along the estuary's southern shore not far from San Felipe, a few kilometers west of Río Lagartos, the boat pulls up to a small dock at the end of a walkway extending into dense mangrove forest. The wooden walkway is elevated because the ground there often is submerged. The walkway leads to a small, open pond in the center of which fresh water constantly gushes to the surface. The pond and its surrounding mangroves are known as Petén Kambulnah, and the place is a destination for boating tours originating from San Felipe.

The freshwater pond abounds with colorful tropical fish constantly splashing and showing their colors, interesting aquatic vegetation, birds who hang around, and the occasional crocodile. At the beginning of the canal draining the freshwater from the spring into the estuary, a sort of oily scum accumulates, as shown at http://www.backyardnature.net/n/15/150329oi.jpg.

Not having a microscope here I can't identify the puffy, air-filled scum, but it's very similar to the cyanobacteria we identified in the Dry Frio River back in Texas. Some cyanobacteria are known to produce oily sheens atop water, so my guess is that that's exactly what we're seeing. Though some cyanobacteria are known to produce toxins that can sicken or even kill animals, the oily sheen at Petén Kambulnah is natural, occurs in unpolluted water and doesn't seem to be hurting anything in the life-filled little pond.

In fact, even up North, especially in periods between rains when water stands for a long time, often you see such perfectly innocent oily sheens, often produced by harmless iron- or manganese-loving bacteria occupying waterlogged soils. Decaying plant and animal material also can create an oily appearance.

Sometimes such oily sheens are interpreted as residue of oil pollution. However, natural oily sheens don't smell like petroleum, plus when poked with a stick, sheens caused by petroleum flow back together, but natural sheens like Petén Kambulnah's stay separated when broken up.

*****

DRUNK ON HABANERO PEPPER
I was corresponding with volunteer identifier Bea in Ontario about a certain seashell that still is a mystery, when I offered a little insight into my everyday life in Río Lagartos. For some reason she found it hilarious, so I'll include it here. Apparently there's just something about other people's self-inflicted miseries that is funny:

"Today no tour so far, so I took a bike ride. Going was very hard, against a tremendous headwind, but returning was easy, though going with the wind, my sweat didn't evaporate. I got completely wet, with the added problem that my sweat is so imbued with essence of habanero pepper that my eyes stung. I kept sweat out of my eyes until my bandanna got drenched, and then there was nothing to do but burn. By the time I got back I could hardly walk because I couldn't open my eyes except for a slit from time to time, else they would burn, so here I came through town bobbing and groping, looking completely drunk, barely able to get the key into the door. Of course a simple shower fixed everything, but now how can I go outside with everyone thinking I'm drunk? And the more I try to look sober, the more proof they'll have that really I'm drunk. So there you have it, true life stranger than fiction."

*****

FEATURED ESSAYS FROM THE PAST:

"Collapsed Dream Homes & Lost Tent Pegs" from the December 8, 2008 Newsletter, at http://www.backyardnature.net/n/p/081208.htm

"Burritos Update" from the December 11, 2006 Newsletter, at http://www.backyardnature.net/n/p/061211.htm

*****

Best wishes to all Newsletter readers,

Jim

All previous Newsletters are archived at http://www.backyardnature.net/n/.