April 11, 2010
The other day I stepped from my door and right above me in a leafless Cedro tree a male bird was gesturing toward two nearby females in a way that most people would interpret as lewd. You can see what I mean at http://www.backyardnature.net/n/10/100411cb.jpg.
The birds were Bronzed Cowbirds, sometimes called Red-eyed Cowbirds, MOLOTHRUS AENEUS, distributed from the southwestern US south to central Panama. They belong to the same genus, Molothrus, as the North's Brown-headed Cowbird, and probably you know that Brown-headed Cowbirds are "brood parasites." That means that female cowbirds lay their eggs in the nests of other bird species, causing the other species to do all the work raising the cowbird young. The female cowbird frequently pierces and thus kills the host's eggs already in the nest.
Bronzed Cowbirds also are rest parasites. So far 82 bird species are known to be parasitized by Bronzed Cowbirds. Thus if any bird species should be guilty of lewdness, we might expect it to be this one, even if we know how anthropomorphic the whole concept of lewdness is.
In the picture the male at the top, left is performing his "bow display." Cornell Lab of Ornithology's Bronzed Cowbird page describes the display as "Directed towards female by male. He first lifts the feathers on the back of the neck, followed by those of the upperparts, and finally those of the underparts. The tail is brought forward and under the body while the wings are arched slightly and head is bent." You can read more about Bronzed Cowbird displays at http://www.birds.cornell.edu/bfl/speciesaccts/brzcow.html.
If you visualize the above description -- the tail brought forward and under the body while the wings are arched slightly and the head bent -- you realize that here we're basically talking about a fully executed pelvic thrust.
But, birds don't have real pelvises and, if the truth be known, the vast majority of bird males don't even have penises (chickens and turkeys notably excepted). In typical bird-sex, males introduce sperm into female bodies by pressing their sexual openings against the female's sexual opening, kiss-like. Usually this is accomplished with the male mounted atop the female, tottering and flapping his wings to keep from slipping off.
You can imagine that the Bronzed Cowbird's bow display is rooted in the interspecific male urge to present himself as big and powerful, and ready to boogie, as well as the interspecific vulnerability of many females to such highly suggestive, macho approaches.
Two or three times weekly I hike a little trail into the woods for about a kilometer, to where there's a little orchard with some water troughs set out for wild animals, who here during the driest part of the dry season need all the help they can get. A large water tank is kept nearby, periodically refilled by a pickup truck that makes its way back there, often scraping its bottom on rocks. With a bucket I carry water from the big tank to the troughs, and these days I'm amazed at how fast the troughs are emptied. I've seen deer drinking there, and lots of birds, and coatis and other critters in the general area.
This week I checked the big tank to see how much water was left and found inside a little treefrog floating at the water's edge. I knew he was a treefrog because of the large, circular pads on the tips of his toes. You can see him, his head barely out of the water, at http://www.backyardnature.net/n/10/100411cq.jpg.
Below the frog's bulging eyes notice the pinkish bulges on both sides. These are parts of the frog's balloon-like "bilobed vocal sac," a vocal sac that bulges on both sides instead of bulging into a single big sac below the throat. The sac is bulging because as I took the picture the frog was croaking, apparently because some splashing I'd done sounded too much like rainfall, and he wanted a mate.
I'd never seen a frog like this but with its narrowed lower body and curious head with a conspicuous Y- shaped marking, it was easy enough to identify in Jonathan Campbell's Amphibians and Reptiles of Northern Guatemala, the Yucatán, and Belize. It's the Yucatán Casqueheaded Treefrog, TRIPRION PETASATUS, the only species of the genus in our area.
In the picture, notice that the frog's head skin is of a different texture than the rest of the body. It's like a shield atop the frog's head -- the "casque" in "casqueheaded." Casque is another name for helmet.
Campbell writes that the species "... finds refuge in holes in trees, where it plugs the opening with its bony casquelike head. The behavior whereby tree holes are plugged in this fashion is called phragmosis. Because the skin on the top of the head is co-ossified with the skull, this frog experiences relatively little moisture loss when sequestered in its hiding places... "
A fine photo showing how sharply defined the head casque is from the rest of the body is at http://www.backyardnature.net/n/10/100411cr.jpg.
Campbell describes Yucatán Casqueheaded Treefrogs as conspicuously absent during most of the year because they "aestivate" (the summer version of "hibernate") in dried mud. He says it breeds after heavy rains from late May through August.
Therefore, this little frog somehow was out of his dried-up mud at a time of year when not many others of his species were likely to be circulating. I'm watching to see if he can call a mate into his tank with him. My anthropomorphic judgment is that in the last picture he looks a bit sad, as if he'd finally realized how badly out of sync he was with his cohorts.
Yucatán Casqueheaded Treefrogs are distributed from the northern Yucatán south through northern Guatemala and Belize to northern Honduras. With such a limited distribution I'd call him an endemic, and it always tickles me to run across endemics.
THREAD SNAKE THREADING A CRACK
Returning from my banana-buying hike to Pisté I was gathering wool with my unfocused eyes scanning just the next couple of feet before me, my view consisting of cracked asphalt at the highway's very edge. Then somehow a crack didn't seem right. I got on my hands and knees and looked closer and still couldn't figure out what was going on -- not until I poked at the crack with my finger and an incredibly small, dark snake writhed out of his crack. You can see him at http://www.backyardnature.net/n/10/100411go.jpg.
He was about three inches long (7 cm), and when I saw a yellow spot on one of his blunt ends I realized I'd seen such a thing before -- down in Chiapas, and before that here in the Yucatán. Neither time had I been able to figure out for sure what species he was, for even with my handlens details were too tiny to make out. A graduate student in California finally identified the snake as LEPTOTYPHLOPS GOUDOTII, in some books called the Goudot's Thread Snake, and in others the Black Worm Snake.
My first sighting of this species had been of an even much smaller individual than this three-inch one. You can see two pictures of it in my hand for scale at http://www.backyardnature.net/mexnat/goudot.htm.
The literature has given me the impression that this species is fairly rare, but having run into it now in several widely separated localities I'm thinking that despite its exotic appearance it must be fairly common. It seems to like disrupted, trashy places, so maybe it's actually becoming more common as time passes.
Also during my banana hike back from Pisté I heard rustling among dry leaves beside the road and was tickled to see a lizard about eight inches long (20 cm), with his narrow, longitudinal lines slightly resembling our racerunners and skinks up North, seen at http://www.backyardnature.net/n/10/100411wh.jpg.
Again in Campbell's book it was easily identifiable as the Yucatán Whiptail, CNEMIDOPHORUS ANGUSTICEPS. Yucatán Whiptails are endemic to the Yucatan Peninsula, northern Guatemala and east-central Belize, so it a petty good find, even though the species is considered common in the northern Yucatán.
Yucatán Whiptails, I learn from Campbell, do some tricky things with their genes. It happens that sometimes female Yucatan Whiptails mate with a completely different species, the Deppe's Whiptail Cnemidophorus deppei. Offspring of these pairings produce populations that may or may not constitute yet a third species, depending on how you define "species." Whether the populations represent a third species or not, the individuals are "parthenogenetic." By parthenogenetic is meant that the populations consist of nothing but females who give birth to only females without the benefit of males. Offspring are genetic clones of their mothers.
Parthenogenesis is relatively common in invertebrates but rare among vertebrates. Most experts assume that parthenogenetic species have arisen fairly recently in evolutionary time, and won't last long now that they're here. One reason for that is that populations with very little genetic diversity can't evolve the usual ways to adapt to changing environments.
Sex exists for a reason, the geneticists say.
PIICH TREES ACQUIRING THEIR EARS
Last January I showed you how our big Piich trees, ENTEROLOBIUM CYCLOCARPUM, were losing their leaves, admitting abundant light onto the forest floor where previously it had been shadowy. Since then most Piich have been completely leafless, but two or three weeks ago they began cluttering their branches with dark, roundish items as seen on a tree near the ruins' entrance at http://www.backyardnature.net/n/10/100411pi.jpg.
A close-up of the items themselves is at http://www.backyardnature.net/n/10/100411pk.jpg.
Those are immature fruits. Since Piich is a member of the Bean Family, the fruits are legumes, but instead of being long and more or less straight like most legumes, these are curled, almost forming circular disks. The bumps on the fruits are enlarging seeds. Some tourist books call the tree "Ear Tree" because of the legumes' looks.
In a month or so the matured legumes will be dark and fall off. If I'm here then I look forward to collecting seeds, roasting them, grinding them, and brewing a nice hot, coffee-like drink from them. I've always read about that but never tried it. Stay tuned.
One further note: While some of our fruiting Piich trees are completely leafless as their legumes mature, others are sprouting the next season's frilly, compound leaves. Rains aren't due for another month or so, so this is a little surprising, especially since fruiting here in the depths of the dry season requires a good bit of water just for the growing fruits. One wonders where the leafing-out Piich get their water. Most other leafless tree species are staying leafless, but then they aren't nearly as large and, presumably, deep-rooted as these big Piich trees.
MANGO TREES FLOWERING
Some of our Mango trees, MANGIFERA INDICA, with their handsome, evergreen, 15-inch long (38 cm), dark-green, almost glossy, slender leaves, nowadays are abundantly mantled with foot-long panicles bearing hundreds of pale yellowish flowers on pink rachises, as shown at http://www.backyardnature.net/n/10/100411mg.jpg.
Back in Querétaro we looked at the delicious world of mango fruits and you may enjoy reviewing that page at http://www.backyardnature.net/q/mango.htm.
Mango trees are members of the Cashew Family, the Anacardiaceae, along with not only Cashews but also Pistachios, the sumacs, and Poison Oak and Poison Ivy. Flowers in the family typically bear 3-5 petals and have their ovaries perched atop "annular disks," which are doughnut-shaped things in the flower's center. Flowers can be unisexual or bisexual. Mango flowers display all those features but add some interesting innovations. You can see a small group of them at http://www.backyardnature.net/n/10/100411mh.jpg.
In that picture, look at the flower at the top, left. The green, spherical ovary -- the future mango -- is easy to make out, its slender style pointing skyward and ending with a tiny stigmatic area where pollen grains germinate. Mango ovaries are unusual in that their styles don't emerge from their centers, but rather a bit to one side. The resulting mango fruit will be a bit lopsided. Note that the green ovary rests atop a yellow, waxy/grainy-looking thing. That's the annular disk, in that flower so well developed that it appears to be oozing out between the five petal bases. The petals when fresh are white with little yellow ridges but in this more mature flower the ridges are turning brown.
Note behind that flower's ovary there's a single stamen, its dark purple, pollen-producing anther attached atop a pale, slender filament. Some mango flowers may have up to five stamens, but usually only one or two are fertile, the others hardly developed. Among all the flowers I examined on this tree I found only one stamen per flower. This is very unusual on flowers with such well developed petals and other parts.
Notice the younger flower at the lower right. That blossom is just like the top one, except that it contains no ovary at all. It's strictly a male, unisexual flower. The yellow glob in the center is the annular disk. The dark flower to the left of it is similarly a male, unisexual flower in which the stamen and annular disk have shriveled up. When a plant bears unisexual flowers mixed with flowers bearing both male and female parts, the plant is said to be polygamous.
At http://www.backyardnature.net/n/10/100411mi.jpg you can see parts of two older panicles where most of the flowers have shriveled and fallen off or are in the process of doing so. Each panicle bears only a few maturing fruits. All the male flowers will shrivel and fall off, and the vast majority of female flowers with ovaries also will shrivel and fall. In the end, each panicle will bear only one or two fruits. In other words, by far most flowers with ovaries, even if they get pollinated, will abort, leaving only the strongest to mature into fruits.
A LITTLE CLOUD OF PURPLE
The other day along a trail deep in the woods the shadowy, gloomy browns before me were abruptly broken by the feather-sized bouquet of purple flowers shown at http://www.backyardnature.net/n/10/100411pu.jpg.
I knew not to look around for the bouquet's source, for this was from a high-climbing, woody vine. I looked straight up -- and still didn't see anything. Not until I lay on my back and with binoculars scanned the canopy directly above, peering through various layers of tree limbs, did I finally make out the source, maybe 30 feet (10 m) up, a wispy little cloud of purple with the blue sky beyond, as shown at http://www.backyardnature.net/n/10/100411pt.jpg.
It was the Queens Wreath, PETREA VOLUBILIS, native to tropical America, including here, but most frequently encountered in tropical gardens. In gardens, if it's trained like a grapevine to form a leafy roof for an outside patio, abundant, foot-long, long-enduring, purplish racemes dangle from the ceiling of dark-green leaves. It's a beautiful effect, and accounts for why the species is planted in the tropics worldwide. Back in Querétaro we encountered Queens Wreath in a garden situation, so you can enjoy a hint of the effect at http://www.backyardnature.net/q/petrea.htm.
In that last picture, notice that in each "flower's" center there's an irregularly shaped item. If I'd had a camera capable of close-ups in Querétaro I'd been able to show that the item at the "flower's" center was -- a flower. In fact, the five-armed items giving the impression of being flowers are actually calyxes with five very long, purple sepals. Usually calyxes and sepals are green and obscure, but not here. A close-up of the actual tiny flower at the calyx's center looks a lot like a verbena flower, which makes sense because Queens Wreath belongs to the Verbena Family, the Verbenaceae.
The little bouquet that had fallen onto the forest floor before me was an older sprig, for the flowers already had fallen off, leaving only the developing ovary surrounded by its colorful calyx tube. You can see how the ovary's old, shriveling stigma and style project from the calyx tube's mouth at http://www.backyardnature.net/n/10/100411pv.jpg.
PANICLES, RACEMES & BEYOND
Reference is made above to panicles of mango-tree flowers, but racemes of Queens Wreath. Panicles and racemes represent two strategies for organizing flowers in flowering heads, or inflorescences.
Think of a matchstick pointing skyward. If flowers have their stems, or pedicels, sprouting directly off the matchstick, the inflorescence would be a raceme. If several or many stems arose from the matchstick, and then the flowers' pedicels sprouted from those branches, the inflorescence would be a panicle.
Panicles, racemes and several other common inflorescence types are represented diagrammatically at http://www.backyardnature.net/inflorsc.htm.
WHAT DO NECTAR-ROBBING BEES MEAN?
Last week we spoke of nectar-robbing carpenter bees. Does Nature's tolerance of such robbery imply that robbery is an acceptable human behavior?
If not, or if the issue is debatable, just how does a disciple of Nature develop a moral code based on Nature's teachings?
The Six Miracles of Nature show the way. It's been awhile since I've evoked the Six Miracles, so here they are:
The Six Miracles of Nature show direction. They speak of a Universe that has gone from simple to complex; from barrenness to diversity; of life that began with a single organism but became a biosphere of very many interdependent organisms; of life that at first was machine-like, but now is capable of imagining, hoping and being inspired...
Nature's disciple, sensing how all the strands of evolution just mentioned harmonize with one another, queries his or her own feelings as to whether a certain behavior in question FEELS harmonious or inharmonious with Nature's general flow.
Visualizing a hand casting dust into empty space, the dust proliferating, coming alive, blossoming into the Universe with all its dimensions, all its living things, more and more feelings and insights, and unseen currents of creativity...
I FEEL that reverence for life is harmonious...
I FEEL that Bach's fugues are harmonious...
I FEEL that learning all I can about the Creation, that paying attention and trying to stay sensitized to the world around me, that keeping my body fit, that struggling against depression and cynicism... are all harmonious with the general direction of Nature's evolutionary flow.
And these FEELINGS enrich me so that the question of whether robbery is appropriate becomes rather moot, for I find that already I have all that's needed.
Best wishes to all Newsletter readers,