The fog comes.

on little coot feet.

You may have already heard the correct quote the way Carl Sandburg originally wrote it— “The fog comes. on little cat feet…” But this is different. This is coot, not cat. And coots have strange and amazing feet.

Well, just look at them—first of all, they are quite big feet, not little feet!

And they are not long and skinny-toed like crow feet. Or wide and webbed like duck feet.

Instead, coots do have skinny toes, but with foldable fins on each toe.  So the contrast with crow feet is clear—coots are water birds.

But the contrast with ducks, those other water birds, is extremely interesting. Ducks have webbed feet, with webbing between the toes. When ducks pick up their feet, or move them forward in the water, the whole foot folds, to reduce drag. Then, as they push back, their feet flatten out again, so they press against a lot of water to propel them forward.

Coots use a more subtle system. For them, foldable skin flaps extend out on either side of the toes. When they lift a foot, or move it forward in the water, the flaps fold, reducing the drag against the water. Then when they push back, the flaps widen out and provide a lot of surface area for propulsion. This also helps them walk confidently over bogs or swamps or other kinds of squishy ground.

Plus, these clever feet are picturesque—green and gray and black and white—with striking patterns and colors for someone we think of as just little monochrone water birds.

Well, yes, not to mention red eyes and a red-brown forehead badge, and a charcoal back and white tailfeathers, and their pleasing football-shaped bodies.

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Who’s standing tall and alone?

A striking sight in the Sonoran desert is a lone saguaro cactus.

Saguaros (Carnegiea gigantea) provide food and shelter to a surprising number of creatures. This includes humans, who harvest their fruit, and use their skeletons for fences and construction.

These cacti have an amazing variety of adaptations to the desert.

First, check out the color of the stems, a pale green, indicating they contain chlorophyll. Since saguaros do not really have leaves, the stems have to do the work of photosynthesizing and producing food. The pale color keeps the plants from absorbing too much hot sunlight and getting burned.

If you look closely, you will see lines of defensive thorns on vertical accordion ridges. The whole plant can expand to hold more water after a good rain, then accordion back in as it uses the water

What you can’t see is the root structure. Instead of sending down a big tap root, like many plants, they send out numerous very long horizontal roots near the surface, to better gather any moisture nearby.

That’s why they’re lonesome looking—they need to grow far apart. And that’s why, in the old days before we realized it was unethical, (now it’s also illegal) people would dig them up in the desert, transplant them, and they would die, because the majority of  the root structure was left behind.

Too Wet!

A surprising limiting factor in some parts of the desert is too much moisture.

Wait, you say, I thought deserts were too dry?

Because there’s usually so little rain, nobody is really prepared for much. So even what might be considered a light rain elsewhere can be enough to flood out desert burrows, nests, hollows, and lowlands. If you are a creature who can move fast, or a plant that can hold its breath, you will get through it.

But even in the desert, rain is not always light. During the summer monsoon months, and a few other times of year, there can be heavy downpours.

And adding to the effect, there’s that old caliche we talked about before. This is the impervious layer of minerals and clay that forms over time a short distance down under the desert surface, and acts as a water-trap. The water can’t sink in–so where it can, it slides off downhill.

With a light rain, you can suddenly get a flash flood. With a heavy, or extended rain, you can get massive dangerous flooding, the kind that kills animals, large as well as small, and washes away trees and cars and buildings.

In the middle of many human habitations in the desert, you will find long empty wild spaces, often called “washes.” These are where the flash floods wash through, carrying away whatever is in their path.

It’s strange, when you think about it, how moisture could be a problem, and a limiting factor, in both directions in the desert.

Or maybe not. Because a lot of living things want conditions that are not too much, or too little. Instead, they want things to be generally within an agreeable range. So when you look at a limiting factor, it can be fun to check if there is another one lurking at the opposite side. Yet another mystery.

Who lives in this cactus?

Who you find living in any particular cactus will depend on when you look.

Many of the large holes in saguaros are originally drilled (although the process sounds more like a jack hammer than a drill) by Gila woodpeckers, who peck into the cactus to hollow out an area for a nest.

One interesting result is that the cactus, always fearful of losing moisture, forms dense scar tissue around the excavated area. This means that when the cactus dies and the flesh falls away, what’s left is the interesting lattice of cactus skeleton, plus an occasional hard rounded shape that looks something like a boot—so it is called a cactus boot. Native people gathered them and used them as containers for liquids.

Back to the cactus-dwellers. While the plant is still alive, these nests drilled inside saguaro cacti are prime real estate, the perfect place to find thorn-protected shelter until the kids grow up and fly away. At first, after the cactus heals and get less gooey, the  Gila Woodpeckers or related birds who excavated the nest holes get first dibs. But later years may bring entirely new sets of residents.

Adiabatic—a what?

If you listen to the explanations given by weather forecasters, you may have heard the word adiabatic.

No, it’s not a disease related to blood sugat—that has a BET in the middle, not a BAT.

Instead, it is one very cool reason that storms suddenly pop up out of a clear sky in the desert.

Adiabatic cooling or warming happens when the pressure on a blob of air increases or decreases. When desert air hits a mountainside and rushes up the mountain, the air expands, gets “thinner” and cools as it rises to a higher elevation.

This means that if there is any moisture in the air, there is less energy to keep it suspended, so the moisture is more likely to condense, and form rain.

The opposite happens when air flows downslope—it warms as the pressure increases because the molecules are closer together and bump into each other more.

Maybe that is one reason that places east of mountains in North America are often more warm and dry than places to the west of mountains. Not only does the moisture get wrung out of the air on the western upslope, even very wet air from the ocean, but following that, some of the moisture on the downslope gets absorbed back into the falling, compressing, warming air.

Cool!

Or rather, cool, then warmer and drier!

 

New Desert Creatures Mysteries e-book

Now you can get a great Desert Creatures Mysteries e-book.

It goes into detail about the strange animals of the desert, and some of the cool science about them.

https://www.smashwords.com/books/view/455225

Leafing so soon?

There are leaves and then there are leaves. And then there are cactus pads, like this wide flat prickly pear cactus pad, which are more like stems than leaves.

Because if you look closely, on the surface of this pad, you will see the actual leaves, small succulent pointy cones, next to their associated thorns, which form in the axil (that’s like the armpit!) of the leaves.

The thorns persist, as most desert dwellers know too well, but the little leaves fall off in a matter of days, another water-saving feature, so only the thorns and the thick-skinned pads, and the quickly hardening new pads, remain.

Stems or not, the pads, after the skin and thorns are very carefully removed, have been used for centuries as food by native civilizations in the desert

 

Spring Planting

Haboob, the Desert Dust Storm

Another limiting factor in the desert arises from the ferocious dessicating and abrasive desert dust storm called the Haboob. Often associated with the seasonal monsoons, these storms can actually happen any time of year, blasting and scouring any plants and animals in their path.

The word haboob is Arabic, from the home of truly impressive sandstorms, but now is applied in any area susceptible to them.

These storms can move particles of dust and even sand, and may reach hurricane force for a few minutes at a time.

Deserts have few trees to stop the wind, and little moisture to hold down the soil. A haboob forms when warm air rises into thunderheads, then the air is cooled by rain, the storm collapses, and the cooled air falls and rushes out from the base of the storm, driving dust and sand before it, sometimes at truly remarkable speeds. Within minutes, winds can go from zero to 50 miles an hour.

Dust storms often arise suddenly, making them hard to avoid or escape. Most years in the Sonoran desert, there are traffic accidents associated with dust storms, when visibility suddenly plummets.

Desert plants need either shelter or thick skins to handle the dessication and scouring associated with a haboob or other winds.

A Dry Heat

The joke is, in the Sonoran desert, even though it’s 114, it’s a dry heat.

The idea being that with very low humidity, amazingly, under 5 percent at times, the heat is easier to bear.

114, an average high for a few days each summer, is still bad enough, but given how few trees and other shelter there is in the desert, it’s almost always a sunny heat during the daytime, which adds another 7 to 10 degrees.

All plants and animals and people that live in the desert need to be built or adapt in some way to survive these extreme temperatures.

The hottest time of year is a few days before the summer Solstice on June 21, and a few weeks after that. Then the average daily temperature starts going down again, very very gradually.

A few weeks after the solstice is also the time when the summer monsoons really get going. The standard definition of monsoon season is the change in the wind, but in the desert, the important thing is that the monsoon usually brings moisture and finally rain from the Gulf of California and the Gulf of Mexico.

And of course, when the humidity goes up and the rains start, it’s still over 100 degrees in the desert. And it’s no longer a dry heat.