Pigeon Week Part 1: Navigation & Magnetic Fields

I have a list of things I want to blog about in this project before I’m done. Some of them I’m not aware of till I see them, but others I’ve been fully aware of since day 1. Pigeons are in the fully-aware category. I originally planned to do a “Pigeon Post.” But when I learned a little bit about Pigeons and how amazing they really are, I just had to declare this Pigeon Week.

Now I know you’re probably thinking, “What? How’s he going to get a whole week out of Pigeons? This sounds lame. I’m so checking out for a week…” Yes, yes, I know- “feathered rats” and all that. But I am telling you, Pigeons are Phenomenally Way Cool, and if you stick with me, by the end of this week you will never look at them the same again. So here we go:

One of the odd things I’ve learned about winter is that it’s actually a really good time to check out birds. On the face of it this makes no sense at all; most birds are gone in the winter. But what I’ve found is that because there are far fewer species of birds about- and far fewer bird-cries in the air- that this somehow makes it easier to really notice the birds that do stick around. Magpies are a great example, as are Scrub Jays and Dark-Eyed Juncos. Pigeons are another. Unlike many of the birds I’ve blogged about, Pigeons aren’t endemic, or even native, to the Western US; they’re everywhere, on all continents except Antarctica, from sea level to 14,000 feet.

When I say “Pigeon” this week, I’ll be talking specifically about the common Rock Dove or Rock Pigeon, Columba livia*. More broadly speaking, “pigeons” and doves- which are really the same thing- are any one of 300+ species within the family Columbidae. Columbids are stout-bodied** birds with short necks, short beaks and a small fleshy protuberance atop the beak called a cere. An example of a native columbid here in Utah is the Mourning Dove, Zenaida macroura***

*An astute reader might ask if I’m talking about wild, domestic or feral C. livia. We’ll get to that in Part 3, but for now assume feral.

**Wikipedia’s term. I was going to say “plump.”

**Which deserves- and hopefully one day will get- a post of its own.

There are so many cool things about Pigeons that it’s hard to know where to begin, so let’s start with something everyone knows: they’re fantastic navigators. We’ve all heard of homing pigeons, and their remarkable ability to return to the home roost from hundreds of miles away, traveling across unfamiliar terrain. Humans have been using pigeons to carry messages for at least 3,000 years* and in doing so have been credited with a critical role in many wars, including both world wars.

*Pigeons have been domesticated for at least 5,000 years, as we’ll talk about in Part 3.

We’ve heard so much about homing pigeons that it’s easy to forget that “homing” isn’t something that suddenly came about when we humans decided to start sending messages around; Pigeons have been regularly using their formidable navigational capabilities for thousands- maybe millions(?)- of years, and in fact use them daily in the wild.

Here’s something cool: we’ve all seen- or maybe see every day- pigeons around cities. Pigeons adapt readily to urban environments, nesting under overpasses or in the eaves of high buildings, as these spots are similar in many ways to the rock ledges and overhangs in which their (truly) wild ancestors nested. For a pigeon, a modern city or town is a wonderfully convenient assemblage of nook-and-cranny filled cliffs, as good as- or better than- any grouping of natural nesting cliffs. But what you maybe didn’t know is that many urban pigeons are commuters- specifically reverse commuters- who each day fly out to suburban or rural areas to forage and then nightly return to their downtown nests. Pigeons navigate for a living.

Tangent: For years I’ve noticed pigeons flying by my office window. But I never really had a handle on where they roosted. Then last week I changed one of my standard running routes, and stumbled upon a big pigeon roost, in the strip mall at 1300 East and 8600 South. And I noticed as well that pigeons really dominate the stretch of 1300 East between 7800 South and 8600 South.

And this in turn has lead to a blazingly-obvious “epiphany” which I somehow never noticed until last week: Birds have neighborhoods throughout developed areas, and in fact certain flocks of certain species dominate specific urban/suburban blocks. I’ve blogged previously about how the local Magpie flock aggressively controls Sunnyside Ave between my house and the zoo. There’s another flock dominating the cottonwoods and willows on Union Creek Road just between I-215 and Ft. Union Blvd, where I exit the freeway for work every day. My standard 5-mile lunch-run loop includes a stretch along 1000 East between 7800 South and 8600 South which is solid Starling territory, although there’s a dense, tightly-controlled, 2-to-3-yard* “cell” of House Sparrows around 8000 South.

*”Yard” in this case as in the yard of a house, not the unit of measurement.

These little “city-states” must change with season and migration throughout the year, and what I’ve realized this past week is that throughout the valley, superimposed upon and around us, is this whole, fantastically complex, dynamic, multi-species, socio-political landscape/map to which 99% of us are completely blind. How did I miss that for so long?

The interesting question is how pigeons navigate, and this question has 2 parts. The first is: how do pigeons navigate mentally? Meaning are they just following a path of memorized cues or landmarks? Or do they construct a mental map of their surroundings and intended destination?

Until the latter half of the 20^th century, it was unclear how pigeons homed. One hypothesis was that pigeons simply homed by following the outbound path they had taken away from the roost. Many animals, such as ants, use this type of Hansel & Gretel approach, following landmarks recognized and/or marked (by scent in the case of ants) on the outward journey. But observation quickly ruled out Hansel & Greteling for pigeons on 2 counts. First, pigeons transported to remote locations blindfolded home just fine. And second, pigeons returning home from the same location multiple times don’t follow the same exact path. (Remember this- we’ll come back to it.)

So pigeons seem to use a mental map. But what sort of map? The simplest “map” in animal navigation is a cue gradient map, in which the animal extrapolates from remembered landmarks or cues to determine location and course. These cues may be visual, olfactory (smell) or magnetic. But a simple cue gradient map is limited as to how far it can be extrapolated, and it doesn’t really require a compass. Pigeons navigate hundreds of miles across unfamiliar terrain, and have not just 1, but 2 internal compasses. Most researchers today agree that pigeons construct true spatial navigation maps.

Tangent: In thinking about animal navigation, it occurred to me that we humans use all three methods: simple track-following, cue-gradient maps, and full spatial-mapping. Here are 3 examples.

Until 2 years ago, my parents lived in the house where I grew up. When I visited once or twice a year, I’d return to their house from the airport (by either taxi or rental car) by simply following the same exact set of landmarks: Callahan Tunnel, 93 North, Mystic Valley Parkway, Right at the Armory, Left at the rotary, past the cemetery, the town-line sign, left at Simms’ Corner, up the hill. But 2 years ago my parents moved across town to a townhome, and I had to think just a little bit more about where I was going. The townhome was still in my hometown, so I didn’t have to consult a map or ask my parents for directions, but I had to reference additional memorized “cues” in getting to their home- the train station, the plant nursery, the street where I first rode a friend’s motorcycle, the intersection where a college student broadsided our Toyota station wagon on the way to church. I don’t exactly go past all of these places, but they’re reference points I think about to get me to the condo. So nowadays I use a cue gradient map of sorts to get to my parents’ place.

Last night I flew into San Jose and took a cab up to a hotel in Santa Clara. Before I left home I checked out a map online to get a feel for the route. Though it was dark when I landed, I paid attention to the turns and direction the driver took, tracking the route along unfamiliar streets using the spatial-navigational map I’d constructed prior to take-off.

Nested Tangent: I’ve traveled hundreds (thousands?) of times for work and pleasure in 47 US states, 26 countries and a couple hundred strange cities/towns, and I almost never use a GPS navigation system. I love route-finding; it’s one of the most enjoyable parts of being human. Really, if you can’t find your way around, I think at some point you have to stop and ask yourself: are you really fully human, or a just a good-looking chimpanzee who somehow learned to speak? (Then again I’m one of those weird guys who hates automatic transmissions, so don’t pay me any mind* if you like GPS’s and I’ve offended you.)

*This is my polite way of saying, “Don’t bother leaving an irate comment.” Or do- whatever makes you feel good. I really just want you to be happy. If you’re a GPS-addict and I’ve offended you, then please go ahead and leave a snarky comment. You’ll be filled with a righteous, well-I-told-him-what, sense of well being, and you won’t hurt my feelings at all. I’m actually happy whenever I get comments, even when it’s that Indian flower-delivery place that spams my comments sometimes.

The second part of the question is how pigeons construct and follow these navigational maps. Are they visual, olfactory, magnetic? The evidence seems pretty conclusive that pigeon maps are both visual & magnetic.

The vision of birds is something I’ve covered in several previous posts, so I won’t spend a lot of time on it here, but the short version is that it blows ours away. Bird vision excels not only in distance and clarity but also in color. We humans are trichomatic*, meaning that our retinas have 3 different kinds of cones, or color-wavelength receptors, which are optimized for (relatively speaking) long, medium and shorter frequencies of visible light. Most other mammals are dichromatic or monochromatic, meaning that we see a more colorful- and possibly more detailed**- picture of the world than they do.

*Most of us, anyway. Plenty of people- mostly men- are dichromats or even monochromats, and some number of women may actually be tetrachromatic, as we discussed in this post.

**When I say “possibly”, I mean it. There’s a case to be made that in at least some instances, decreased sensitivity to color enables one to notice detail less clear to those with full color vision. The classic example is colorblind aviators in WWII bomber crews who were supposedly better able to spot camouflaged targets.

But pigeons have 5 different cone types, making them pentachromatic, and what’s more, they have specialized color-tinted oil droplets covering some of their retinal cones which shift wavelengths of light before they reach those cones, thereby optimizing those cones for yet additional wavelengths. In the case of pigeons, it appears that their eyes are therefore effectively at least octochromatic, meaning that they see a world with almost 3 times as many colors as you or I.

At the risk of belaboring the obvious, pigeons- and all flying birds- have yet another visual advantage over us: they’re way high up, and so able to visually map on a scale rarely available to us ground-dwellers.

But really, all of that is review; what I want to focus on in this post is magnetic navigation. For nearly 2 centuries naturalists have suspected the Earth’s magnetic field to be implicated in the navigation of many birds, and in fact it appears that not just birds, but also salmon, turtles and even honeybees* utilize magnetic field clues in route-finding.

*The navigation of honeybees is worth a post in itself, and is way complicated. Though I haven’t really researched it, I stumbled across enough references in researching this post that I suspect it involves elements of all 3 mental navigation models- path-tracking, cue-gradients, and spatial-mapping. Like pigeons, it appears to involve at least 2 compasses- visual/solar and magnetic, and even more interestingly, as honeybee vision (they have apposition compound eyes, which I explained in this post) extends into UV wavelengths, the visual/solar compass is still effective on overcast days.

But before we talk about how pigeons “see” a magnetic field, what exactly is the Earth’s magnetic field?

All About The Earth’s Magnetic Field

Way back when the Earth was molten blob, the heavier elements of the blob- including iron*, nickel and cobalt- sank to the core. These elements are ferromagnetic**, meaning that they can be magnetized- and remain so- by a magnetic field. The core of the Earth is still molten, and these molten ferromagnetic elements are moved around through the core- specifically the outer core- by convection currents, which generates a magnetic field.

*Iron BTW is pretty common in the universe because it’s the final, un-fuse-able end product of really, really big stars, as we saw when we covered Orion and supernovas. Like all heavy elements, Iron is the product of exploded stars. Think about that- all the Iron in your life- you car, tools, maybe your bike- was once stuff in a monster-sized star that blew up.

**An atom of a ferromagnetic element possesses electrons in its outer electron shell, yet the next inner shell is not filled, which means that its electron spin moment is not cancelled.

This convection-generated field extends far out into space, deflecting (to our benefit) most of the cosmic rays headed toward Earth. The field has a direction, with an approximate “North” and “South” pole, sort of (but not really) like a bar magnet.

Not all planets BTW have magnetic fields. Venus has a mainly iron core, like Earth, but no magnetic field. It’s thought that Venus’ extremely slow rotation (roughly as long as its year) is too slow to churn things up and get the necessary convection currents going in the outer core. That’s the thinking anyway. In truth much about the Earth’s magnetic field is a mystery, including its alignment and direction. Most people know that the Earth’s magnetic and geographic poles don’t line up exactly right. Right now the Magnetic North pole is somewhere in Greenland up around 79 degrees North. That’s why you need to know the variance between geographic and magnetic North poles (declination) at your location to use a compass accurately. But what’s weird about the magnetic poles is that they’re moving- fast. Since 1831 (when the North Magnetic Pole was located) it’s moved an average of 6 kilometers per year, meandering about (apparently) aimlessly some 1,000 km. Even weirder, it’s speeding up; in recent years it’s been moving more like 24 km/year.

Weirder still, every once in a while the Earth’s magnetic field flips, or reverses. It’s not clear why this happens- everything from Chaos Theory to asteroid impacts has been suggested- but the field has reversed more than 71 times in the last 171 million years. And bizarrely, the reversals don’t happen at regular intervals. Between 120 million and 83 million years ago, the field never reversed once. But around 42 million years ago, the field reversed 17 times over just 3 million years. Why is the pole moving faster now? Is it getting ready to flip again? We don’t know.

Speaking of “poles”, the term is a bit of a misnomer. There really is no magnetic pole “point” you can go stand or plant a flag on; it’s really just the sum or average of the many, many magnetic dipoles aligned by the core-convection processes. A similar misconception is that a compass points to that magnetic pole, as if there were a big underground magnet up in Greenland yanking on the needle. But that’s not really what’s happening; rather your compass-needle is aligning with the magnetic lines of force at your location.

The magnetic field varies in intensity and inclination- or “dip”- across the globe. The field is 3 times as strong in Antarctica for example as it is in Brazil. And while the magnetic lines of force are oriented almost perpendicularly to the Earth’s surface in Antarctica (~90 degree dip), they’re almost parallel in Brazil.

On a local level, the field varies quite a bit. Natural geologic features including mountain ranges and ore deposits have distinct magnetic signatures, lending to regional magnetic topographies. Many of the loudest/brightest magnetic features are man-made, including bridges, buildings, railways and transmission lines. And at a local level, magnetic field details can fluctuate a bit from day to day. (Remember this too- we’re coming back to it as well.)

Side Note: In fact an ice axe or even a large belt buckle can throw off a handheld magnetic compass by as much as 3 or 4 degrees.

Wow, the Earth’s Magnetic Field is way freaky. What was I talking about again? Oh right- pigeons.

So how do we know pigeons navigate magnetically? Because we can mess them up. When pigeons have bar magnets strapped to their heads, their navigation is totally messed up, but only- get this- on overcast days. That’s right, pigeons can manage just fine with their solar compass even if their magnetic compass is jacked, but when they lose sight of the sun, they appear to rely solely on their magnetic compass.

Interestingly the converse is also true. A pigeon’s solar compass is calibrated by its internal biological clock; in other words it knows where the sun is supposed to be at a given time of day. Clock-shifted pigeons, whose day/night cycle has been shifted by isolation and/or relocation (think jetlag), also experience jacked-up navigational ability, but only on sunny days. On overcast days, the clock-shifted pigeons do just fine, because they’re navigating magnetically.

Extra Detail: BTW, the strapping-a-magnet-to-your-head experiment has been tried in all sorts of interesting variants. One version involved strapping a coil* around the bird’s head that effectively reversed the magnetic field, and sure enough, when released on an overcast day they flew 180 degrees away from home. Other versions have entailed blasting pigeon-heads with magnetic blasting prior to release, which seems also to mess them up, though less dramatically. Similar experiments have been conducted with humans- applying magnets or magnetic fields to their heads, transporting them to unfamiliar locations, and testing their navigation/homing skills, but the results have been mixed.

*Specifically a Hemholtz coil.

The magnetic sense of a pigeon seems to be much more than a simple compass. On a large scale magnetic dip angle provides approximate latitude and the mental navigational map of a pigeon appears to incorporate local, small-scale magnetic features and anomalies. Remember how I mentioned earlier that pigeons don’t always follow the same route home? And then how I mentioned that local magnetic fields fluctuate a bit from day to day? It’s suspected that those fluctuations may account for the route variation. (Wow.)

But how do pigeons sense magnetic fields? For a long time the prime suspects were specialized receptors on either the retina or somewhere along the neural networks (usually the trigeminal nerve) in the face/head. But research in the last decade appears to implicate the beak. The top of a pigeon’s beak contains numerous very small (1-3 micrometers across) nodules of biogenic*magnetite, the iron oxide (specifically Fe3O4) of which lodestones are comprised, and the most magnetic naturally-occurring material.

*Just means of biological origin. So not like the 6-million-dollar man’s eye, or my father-in-law’s knees.

The magnetite-beak connection wasn’t an obvious one. For many years one of the leading alternative explanations to magnetic navigation in pigeons was olfactory navigation. When pigeon beaks were anesthetized, their navigational abilities were impaired, which lent support to the olfactory-navigation hypothesis. But anesthetizing the beak was also anesthetizing the nerves leading to the magnetite nodules, impairing the magnetic sense of the poor* birds.

*And I mean it. When you spend a few days reading about all the annoying and nasty things scientists have done to these poor birds, you really start to feel for them. It’s no wonder they crap while flying over us.

So in the last decade, our understanding of how pigeons appear to utilize magnetic fields appears to be becoming clearer. But none of this tells me what I really want to know: How does a pigeon see magnetic fields and features? What does it look, or feel, like? How does the bird experience a magnetic mental map??

Does a pigeon feel magnetism, as we might feel a breeze on the face, or texture when we run our fingers across a tablecloth? Or is it a slight tug or pull or pressure transmitted to the beak in a more indirect way, like how the “texture” of a rocky trail is transmitted to my hands through the wheel, fork and handlebars of a mountain bike? Or does it smell magnetism, meaning does it come across like a scent of something familiar or welcoming or acrid or spicy?

Or, does it really see magnetism? And while it’s impossible to know, neural networks provide a tantalizing hint. The magnetite receptors in the beak are connected to the underside of the pigeon’s brain by nerves branching off the trigeminal nerve, the main nerve hooking up most everything in the head/face, and one of the dozen main nerve-paths connected directly to the brainstem (as opposed to the spinal cord) in most* land/air-dwelling vertebrates, including us. The trigeminal nerves breaks into many, many pathways in its various connections, but these pathways are grouped into several main branches. The magnetite receptor nerves link into the ophthalmic branch of the trigeminal nerve, the same branch shared by- that’s right- the eyes.

*Specifically there are a dozen in amniotes, which are tetrapod vertebrates with- or descended from creatures with- a terrestrially-adapted egg. So reptiles, mammals and birds. Other vertebrates have different numbers.

So perhaps pigeons really see magnetic direction and topography. Maybe, just maybe, it’s superimposed upon, and integrated with, the already-unbelievably-fantastic octochromatic visual image the bird has of the world. An image more detailed, more comprehensive, more sophisticated and perhaps more beautiful than anything we can ever even imagine.

When released far from home a homing pigeon circles the release point a few times, presumably getting its bearings, before flying off on an initial heading within a degree or so of home. I like to think about the image the bird must see as it circles, the little ah-ha moment it must experience as it aligns its world-view with its mental map and aims for home.

So. Are you starting to see how Pigeons might be way cool yet? Let me tell you what- we are just getting started.

Next Up: Gender, Souls and the Parallel Evolution of Milk.

Gone

There it is- my first week without a real post in 22 months. Well, at least I got an Astro-Graphic in.

Wednesday night I peeked outside a few times, but the sky was always cloudy. On last night’s drive home I noticed the sky was clearing and thought happily about how I’d get to check out the P/2010 A2 debris trail again. But after dinner, outside with glasses and binoculars, I scanned the clear sky just South of Cassiopeia again and again to no avail. Though I might possibly have caught one tiny blur through the lenses, it could well have been some distant cluster or galaxy instead; the fabulous splash across Tuesday night’s sky was gone.

I should feel lucky, fortunate to have spotted- without trying- something possibly never observed before in modern times. But instead I just feel deflated. It was so fleeting, so quick, that it somehow made me think of time passed by, chances not taken, opportunities squandered.

It was beautiful. When I spotted it I emailed and texted several friends who I thought might find it beautiful as well. 2 of them* maybe-might-have seen it, but the rest missed it.

*SkiBikeJunkie & Hunky Neighbor.

Awesome Wife was out with friends last night, and a bit later the Trifecta and I went out in the hot tub. They picked out Orion, Mars, the Pleiades and a few other stars I’ve droned on about over so many other nights in the tub, lifting my spirits by filling me with a bit of geeky science-dad pride. At one point Twin B was trying to point out something directly overhead and the four of us all craned our necks, staring straight up. At that exact moment, a bright, slow-moving meteor streaked across the top of the sky, coming in from the West and passing directly overhead before flaring out due East up at about 75 degrees.

Shooting stars aren’t rare of course, but it is rare to see a spectacular one from down in the light-polluted valley. And usually when you’re with a group, and you- or one of your companions- spots a shooting star, you/they are the only one to see it- it’s flared out before you can call their attention to it. So for us to see one- a high-in-the-sky, slow-moving one- all at the same time, was an unusual and beautiful thing. More beautiful somehow even than Tuesday night’s once-in-a-lifetime impact/debris trail. The Beauty of the World is wonderful whenever and however you see it, but it’s even stronger and more beautiful when you see it together with people you care about.

Tonight: Look Up

Last night around 8:30 we were out in the hot tub. The Trifecta were jumping around and splashing. Awesome Wife turned up the jets, closed her eyes, and tried to pretend the rest of us weren’t in the tub with her. I stared up at the sky. There were patchy thin clouds moving in and out and in the West about 45 degrees up in the sky there was one really straight wisp of cloud that didn’t seem to be moving. I watched it for maybe 5 minutes straight and it didn’t budge.

I got out of the tub, checked out space.com and learned it was this, the impact/debris trail from a probable very recent asteroid collision, 90 million miles away, between the orbits of Mars* and Jupiter. Here’s a quick locator-graphic to help you find it. It’s pretty faint to the naked eye, but I saw it in a light-polluted area without my glasses (I’m slightly near-sighted.) It’s quite clear with binoculars.

*Note that I said the “orbits” of Mars and Jupiter- not the planets themselves. Right now Mars is on the opposite side of the sky in early evening, just rising in the East. It’s the big orange honking “star” just below Gemini. I’ll do a post on it soon.

This is the first time such a collision’s ever been observed, and it may well be that another such event is not seen while we’re around to see it. I expect it’ll be visible tonight as well, so get outside and check it out.

I Like February

No, I don’t have a real post. I’m just goofing around today.

I’m always happy when February comes around. Part of this is probably just where it sits on the calendar. Only 2 months till April! Soon there’ll be birds and bugs and flowers and everything else. The days are longer now, and with the sun higher, the world doesn’t seem so harshly divided between glaring light and dark shadow; it’s like there are colors again. The inversions seem to ease up, and it’s not quite so cold as it was just a month ago; almost every day breaks freezing now.

Winter has finally become kind of pleasant the last week or so. The recent storms have cleaned the gunk out of the air, and put down enough snow that skiing is fun again.

Tangent: And that’s important, especially right now. Because one downside of Utah in late January and February is that, living here, you are exposed firsthand to a whole bunch of really, really, really crazy people. Oh no, I don’t mean that Utahns are crazier than folks anywhere else- every state has its share of crazies. But here in Utah, for 6 weeks every winter, we pull together several dozen of the most absolutely wacky, living-on-another-planet, bat-shit-craziest people from all over the state, put them all together in one building and then broadcast them on TV every night. We call this group the “State Legislature”, and it’s absolutely critical that you avoid watching the evening news during this period, lest you freak out, abandon your house and move out of state.

Last week, someone asked me- not for the first time- if I could ever see myself moving to [THE NORTHEASTERN STATE WHERE MY NEW EMPLOYER IS HEADQUARTERED]. Whenever someone asks me that, I always think the same thing: “This person does not know anything about me or my values.” I try to explain it sometimes, but it never gets across. People just have to “get” it for themselves.

Fortunately for them, I now have a helmet-cam. Here’s what I saw yesterday morning at 8:13AM. At 2 seconds the view pans to the right and down Big Cottonwood Canyon clear out to the Salt Lake Valley. 20,000 years ago a glacier filled this canyon, and spilled about a kilometer past its mouth, where it (presumably) calved off icebergs into the ~700 – 1,000 ft deep lake that filled the valley bottom. At 8 seconds the view turns to the left, toward the sun breaking through the hoar-frosted aspens.

At 9:03AM I walked into the office. There’s no other million+ person metro area in the US where you can pull that off. That almost- almost- makes up for having Orrin Hatch as your senator.

No I’m not posting the whole ~15 minute descent. But here’s a quick 30-second stretch about 5 minutes down the mountain that gives you a feel for the terrain.

Lastly (in a lame effort to add some minimal science value to an otherwise wholly frivolous post) I’ve mentioned before about the odd lack of pines in the Wasatch, and how one really noticeable exception is the stand of planted Ponderosas directly across from the entrance to The Spruces campground/ parking area. In this clip I glide alongside them, pointing my pole up and at them as I pass by. This one’s just for tree geeks, but I thought the light through the trees was kind of pretty. I let the clip* continue down to the road so you’d know just how close to the road the stand is.

*Sorry about the herky-jerky. Goggle-strap wasn’t tight enough, and the cam bounced a bit as I skied over some stutter-bumps.

The cool thing about doing something like this before work is that even if the work-day turns out kinda-sorta-sucky*, the day is still wonderful.

*And it was.

Sonoran Twin B Getaway Part 2: Why So Spiky?

I’d like to ask you to start today’s post with a Thought Experiment. That’s where you think about something, and do sort of a what-if? about the thing you’re thinking about. No, no, not yet- I have to tell you what to think about.

Tangent: I love thought experiments, and here’s why. I love science, and I love the idea of being all kind of science-y and conducting experiments. But I’m also lazy and disorganized, and Real Experiments involve things like materials and effort and time and patience and preparation and what-not. So for me, Real Experiments- with the exception of zero-preparation stream-of-consciousness experiments*- are pretty much off the table.

*i.e. “What will happen if I ride my bicycle down these stairs?”, or “How will my spouse react if I am 2 hours late?”, or ”If I keep nodding, will my coworkers assume I understand what they’re talking about?”

But Thought Experiments are right up my alley. I can conduct them anyplace, anytime, with no preparation, fuss, risk of injury or clean-up.

Nested Tangent: And in fact I do. If you are one of my several lurking coworker readers, you should know that I frequently conduct thought experiments while at work, usually while in meetings with you. You’ll be going on and on about who-knows-what, and I’ll be totally tuned out, imagining what would happen if an ostrich were to pilot a nuclear submarine under the Arctic ice-pack, or how many coworkers I’d hit if I pulled that dead cat out of my laptop-case and started swinging it in a circle around me. Usually I’ll cover by staring at you intently with my brow slightly furrowed, as if you’re sharing some remarkable, life-changing insight that will fundamentally revolutionize our business, But really, you never are*.

*Because- and here is one of those remarkable footnoted nuggets of insight that just makes this blog so phenomenally worthwhile- anyone at any job in any company who has something worthwhile to say says it in under 90 seconds. After that, they’re just blathering.

But Thought Experiments aren’t just screwing around. Schrodinger’s Cat and the Twin Paradox are 2 well-known examples of Thought Experiments that are taken seriously by Real Actual Scientists. So pay attention and stick with me.

Imagine that you’re riding a mountain bike along a winding singletrack trail through a desert (i.e. no big trees, or shrubs taller than you are, and no big boulders or sharp rocks). You’re just riding along at maybe 15 MPH, when you miss a turn, go over the bars and go crashing into a typical patch of vegetation. How badly are you hurt?

Before you answer, I want you to run the experiment 3 different ways:

1- In the Great Basin Desert, say on Antelope Island in the Great Salt Lake

2- In the Mojave Desert, say on Barrel Roll trail, just outside of St. George, UT.

3- In the Sonoran Desert, say on one of the trails through the McDowell Mountain Preserve, just outside of Phoenix.

In the first example- as I can tell you from first-hand experience, you’re probably just fine. You may have landed in a patch of Sagebrush, Rabbitbrush or Bitterbrush, and while you may be a little scraped and bruised, you’re likely to dust off and be on your way promptly.

In the second example, you might be a bit more scratched up. You may well have crashed into a bunch of Blackbrush or maybe even- if you’re unlucky- a stand of yucca or even a patch of prickly-pear cactus. So you may need to spend a few minutes cleaning up, or even break out the tweezers and pull out a few thorns.

In the third example, man are you in a world of hurt. Seriously, if you fly off your bike and land on a big old Teddy Bear Cholla, Cylindropuntia bigelovii, I don’t know what you do. Start praying I guess, because you are in for a long, slow, excruciatingly painful process of disengagement.

This thought experiment may seem kind of “so-what”, but it highlights the question that always bugs me about the Sonoran: Why is it that the further South you go, and the hotter it gets, the desert gets spikier/sharper/spinier? Think about it. There’s just no comparison between the general spiny-ness of plants in open spaces around Salt Lake Valley, and those around Phoenix. Why is that?

Why So Spiky?

You would think that a question this basic would have a real easy, obvious answer. It doesn’t. I’ve googled every possible combination of “spines”, “thorns”, “Sonoran”, “desert”, “reason”, “why”, “evolution”, “plant”, “cactus” and about a dozen other terms. I’ve got a dozen+ great books on plants and deserts. Nowhere have I found a simple clear explanation for why the Sonoran is so darn spiky.

Typical “answers” read something like this: “Desert plants have adapted to their harsh environments with defensive measures such as spines and thorns to protect them from predators…” Yeah, so what? Predators of plants live in lots of environments- jungles, forests, grasslands, swamps- why aren’t those plants spiky? And even if there is some reason for specifically desert plants to be spiky, why are the Sonoran Desert plants so much spikier than those of other North American deserts?

Side Note: I’ve mainly ignored the Chihuahuan Desert in this post, only because I have the least familiarity with it, having hiked in it exactly once, for 2 days, 20 years ago. From what I know and remember, it is both hot and spiky, though not as spiky as the Sonoran.

All About Spines

People often use the words “spine” and “thorn” interchangeably, but they’re 2 different things. Cacti have spines, not thorns. A Cactus spine is a modified leaf that is dry, woody, and doesn’t contain chlorophyll. That much botanists agree on*. How cactus spines evolved is a much more complicated and as yet un-resolved question.

*The other main theory is that the spines are modified bud-scales, but since bud-scales are themselves modified leaves, it’s kind of the same thing.

Cactus spines lack nearly all of the standard features common to leaves. They have no xylem, phloem or stomates- just woody tissue*. In a mature spine, all of the cells are dead, and even when growing, the living cells/new growth is only at the base**.

*Technically, they’re “woody tissue”, but not “wood”, because they don’t have all the features of wood either (example = no vessel elements.)

**This is really cool when you think about it. Cacti are dicots. In dicots new leaf growth occurs at the edges. In monocots, like grass, or yucca, new leaf growth occurs only at the base of the leaf. Have cacti re-invented the monocot trick? It’s even more interesting, because many cacti also grow “regular” leaves, and these leaves grow like normal dicot leaves- from the edges.

Somehow in the course of cactus spine evolution, the genes for leaf-type features got turned off, and the genes for woody-tissue-type features got turned on. How this change came about is still unknown.

Extra Detail: The common ancestor is thought to have been a woody New World shrub which some 50 million years ago evolved the areole*, the distinctive component out of which spines grow on all cacti. The evolution of the areole meant that cacti were able to grow large numbers of spines more quickly and efficiently than they would be able to grow them directly from the stem (like leaves.) The common ancestor is thought to have resembled a Lemon Vine, Pereskia aculeata.

*No, not the thing around your nipples- that’s the areola.

BTW in Part 1 I mentioned how Sonoran cacti are divided into Cereus (columnar) and Opuntia (segmented). These 2 types have different spines. Cereus have only big, visible spines. Opuntia have the big ones, as well as little teeny fine spines, called glochids. Some Beavertail/Prickly-Pear species appear to be spine-less, but actually lack just the large spines; they still have glochids. This is why you don’t want to grab an apparently “spine-less” Prickly-Pear pad with your bare hand.

OK, so we know what cactus spines are. Now, what are they for? Duh. Easy question right? Defense, of course. Well yes, but not only defense, and in fact it’s not clear if defense was the initial driver in the evolution of spines from leaves.

A common mistake people make when buying small cacti from nurseries is to place them in the direct sun. Nursery cacti are shaded, and need to adjust to strong sunlight. The most important way they adjust is by growing more spines, because spines shade the plant. On many cacti, the most important function of spines is to shield the plant from the full sun. This may sound counterintuitive at first; after all those spines are so skinny. But think again of our biking nemesis, the Teddy Bear Cholla.

If you ever walk up to one and try to touch a finger to the “body” of the plant, it’s virtually impossible; the plant is thoroughly covered with spines. And while each spine is a skinny little needle, the matrix-like cover provided by thousands of them creates substantial shade.

Why spines for shade? Why not just leaves? Because leaves are alive, and living tissue requires- among other things- water. Yes, Jojoba, Creosote and other plants manage to grow and sustain living leaves in dry conditions, but no living leaf is as water-efficient as a dead spine.

Cactus spines serve other functions as well, one of the more interesting of which is reproduction. Many species in the Opuntia group (explained in last post) including chollas and beavertails, reproduce asexually by dropping loosely-attached segments. These segment either hang off the plant or drop to the ground, where, in either case, their barbed spines latch on to any animal or shoe that happens to brush against them. On Saturday’s hike we picked up such “passengers” several times, which we carefully removed from our shoes, often dozens of yards from where we picked them up.

Tangent: BTW, speaking of getting around in the Sonoran, know what’s a great way to move fast in cholla-country? Stotting. Check out this Mule Deer moving.

If a segment lands in a suitable location, it can take root and develop into a new, genetically identical plant.

In fact many of the cholla species you see in the Sonoran reproduce primarily in this manner. The vast majority of Teddy Bear Cholla you come across in Southern Arizona are infertile chromosomal triploids that came about via dropped/carried segments.

Side Note: For long-time readers, if this reminds you of something, it should: Dandelions, of which here in North America the ones we come across are overwhelmingly also chromosomal asexual triploids. The analogy is imperfect though: Cholla reproduces by segmenting, while Dandelions create fertile seeds through apomixis*. Triploid dandelions also frequently produce viable (diploid) pollen, enabling them to fertilize the (haploid) ovules of any diploid dandelions they should happen to encounter, and thereby founding new triploid lines. I have no idea if the same is the case with Teddy Bear Cholla.

*Technically agamospermy in angiosperms.

Spines may serve other functions. It’s been postulated they help collect dew, and maybe even retain heat on cold desert nights. Regardless, it’s clear that for many species of cactus, spines serve important functions. It’s also clear that cacti, with their succulence, CAM photosynthesis, shallow rain-leveraging roots and other xerophytic adaptations, do well in the Sonoran, much better than many other plants. So maybe the reason the Sonoran is so spiky is simply because there are a lot of cacti, and cacti generally have spines.

But then there’s thorns.

All About Thorns

Many, many non-cacti in the Sonoran are also spiky. Ocotillo, Fouquieria splendens, is one example; Mesquite (genus = Prosopis), Catclaw Acacia (Acacia greggii), Ironwood (Olneya tesota) and Crucifixion Thorn (Canotia holacantha) are just a few of the many, many others. Unlike cacti, these plants don’t have spines; they have thorns.

Whereas spines are modified leaves, thorns are modified branches. They’re all over the place in the Sonoran. In general, if you plunge/crash into a thicket of non-cacti shrubs/shrees down in Southern Arizona, you’re going to get pretty scratched up, if not outright stuck. (Contrast that with a trailside crash in the Wasatch, say up around Pinebrook or Park City. Ninebark, Serviceberry, Chokecherry- it’s hard to think of anything thorny you’ll crash into, with the occasional exception of Wild Rose*…)

*Actually, just to complicate things, Rose-thorns are- botanically speaking- not thorns. They’re prickles. A thorn is a modified branch. A prickle is an extension of the stem’s cortex. Though they look similar and serve the same defensive function, they’re structurally 2 different things.

Side Note: For years I’ve had trouble telling the some of the most common Sonoran-thorny-things, such as Ironwood, Mesquite and Catclaw Acacia, apart. Part of that’s because I just don’t spend enough time down South, but in fairness, they’re all vaguely similar, with small, dull/light-green pinnately-compound* leaves. With a little patience and a decent plant guide they’re not too hard to tell apart, but last weekend I came up with a real quick & easy way to tell them apart- by their thorns. And since this is when you most often notice them- when they stick you- it’s a helpful distinction.

*See this post for explanation of “pinnately-compound.”

Mesquite thorns are always straight. They stick straight out/up, don’t curve, and hurt. But they don’t stick to you or your clothing, so you can extricate yourself quickly. Catclaw Acacia thorns on the other hand, are curved, just like- that’s right- a cat’s claw. And because they’re curved, they grab onto you, or your pack, or your hat or clothing, and they don’t let go.

The harder you struggle the more they dig in, and the more stuck you become. To extricate yourself, you need to stop, take a deep breath, and methodically, slowly, quietly focus on disconnecting one thorn at a time. (Better yet, ask a friend for help.)

Nested Side Note: Many desert rats also call CC Acacia “Wait-A-Minute Bush”, but Wait-A-Minute’s actually a different plant, Mimosa biuncifera.

Ironwood thorns are also curved, but not so much so. And on mature trees they only seem to grow on the younger shoots, so they’re less likely to snag feet or legs when passing by a mature tree. Ironwood, BTW, is a cool tree in general. It’s wood is super-dense- enough so to sink in water, like our own Curlleaf Mountain Mahogany back here in the Wasatch. Several sources claim it’s the best desert wood for grilling steaks- even better than mesquite- with slow-burning, long-lasting coals.

Another cool thing about Ironwood is that it has right around the same level of cold/frost tolerance as citrus trees, so its presence is a good indication as to whether citrus farming is viable at a given latitude and elevation.

Unlike spines, thorns don’t seem to serve much purpose other than defense. And even without spines or thorns, it seems as though Sonoran plants still manage to find ways of being sharp and spiky. Shrub Live Oak, which isn’t common in the Superstitions, but was all over the place when AS and I hiked in the Ajo Mountains* to the Southwest of Phoenix a couple years back, has tough, stiff leaves whose tips have become fairly sharp points.

*The oak in the Ajos is real interesting, BTW. It’s the same Shrub Live Oak, Quercus turbinella, we get in Southwest Utah, but slightly different. For a while it was considered a distinct, endemic species- Q. ajoensis- but is now considered a subspecies of Q. turbinella. (Somewhere I have some great photos from that trip of the distinctive leaves, but can’t locate them just now…)

And even the stem tips/ends of Palo Verde are disturbingly pointy. It’s almost like everything growing in the Sonoran is sharp and pointed at you.

Side Note: Two notable exceptions are Creosote and Jojoba, both of which as it turns out are formidable chemical warriors. Creosote we’ve looked at previously. Jojoba distinct wax/oil makes its nuts indigestible to animals, with the notable exception of Bailey’s Pocket Mouse (pic right, not mine), which has evolved the ability to digest it.

So why all the anger? What is it about the Sonoran that makes it so exceptionally spiky? As I said earlier, I couldn’t get a clear easy answer. And as longtime readers know, whenever I can’t find an answer, I come up with a Half-Baked Theory. So here we go:

First off, there has to be a reason. Growing spines or thorns has a benefit and a cost. The benefit is that you may live longer, but the cost is that the energy and resources spent growing spines/thorns is energy/resources that could be spent growing something else- like flowers and seeds. (Think about a Dandelion: thorn-less, spine-less, good to eat, but it’s done great by growing lots of seeds.) In the Sonoran, some condition(s) has tipped the balance more toward the benefit side of spines/thorns than in other North American desert; things with thorns/spines have reproduced more successfully.

The Sonoran is dry, but it isn’t the driest desert North America. It is the hottest and the most botanically diverse desert in North America. (I should say the most consistently hottest; the Mojave can experience higher extremes, but the average temperatures in the Sonoran are greater.)

Side Note: Why it’s more botanically diverse is part of a broader, unsettled question of why biodiversity- in all biomes- tends to increase as one gets closer to the equator, and decreases the farther from it one gets. Quick trivia factoid: Mexico has 698 native cactus species. The US has only 191. Guess how many Canada has? First right answer = WatcherSTICKER*.

*What, you already have a WatcherSTICKER? Then you don’t get a prize, but have the consolation of being Way Cool.

When you walk across the open Sonoran Desert, the shrub spacing is greater- on average- than in the Great Basin or Mojave*, and as we saw last post, that spacing is determined by competition for water. So while not the driest, it’s not unreasonable to assume that the Sonoran routinely experiences the greatest competitive water stress, in part due to the heat and maybe(?) due to the (possibly related) greater botanical diversity as well.

*With the exception of obvious localized extremes, such as playas, mud-flats and other unusually barren and/or saline areas.

The competitive water stress, as we saw in the last post, determines to a large which plant grows in what spot. And when the stress is high, the number of possible “new spots” is reduced. The most vulnerable period of a plant’s life is early on, when it first germinates and starts growing as a young shoot. And when the number of potential “new spots” is so limited, the chances of any existing, established plant managing to reproduce in a given year is similarly reduced.

With a lower chance per year/season of successfully reproducing, the plants likeliest to successfully reproduce would be those who lived long enough to attempt reproduction many times over many seasons. So in such an environment, if you managed to germinate and get established, it would pay to stay alive and established for as many seasons as possible. Or in other words, in the poor reproductive environment created by intense competitive water stress, long life and modest fecundity pay off better than short life and high fecundity.

That’s my half-baked theory anyway. It was a great trip. Can’t wait to get back.

Sonoran Twin B Getaway Part 1: Water and Hidden Order

Friday afternoon I snuck out of work early, swung by the house, picked up Twin B and headed for the airport. A couple of hours later Arizona Steve (AS) picked us up at the Phoenix airport.

All About Twin B

Tangent: This trip was a while in the making. Back in September I did solo camping trips with both Twin A (Henry Mountains) and Bird Whisperer (Powell Point.) I intended to follow up sooner with a solo trip with Twin B, but schedules and commitments conspired to delay the trip into the new year.

Throughout this project, I’ve blogged about Twin B the least of the Trifecta. There’s a simple reason for this: She’s the easiest of our children. She’s bright, courteous, responsible, healthy and low-drama*. The unfortunate thing about being a problem-free kid- particularly if you’re not the oldest- is that you probably end up enjoying less attention and focus than your more maintenance-intensive siblings. We’ve tried hard not to make that the case with Twin B, and solo trips, such as this past weekend, as well as a mommy-daughter trip to San Francisco last month, are one tool we use to try to ensure focus and attention on each kid.

*If you don’t know me in real life, you should know that this- “low-drama”- is one of the greatest compliments I give.

Nested Tangent: BTW, this is probably the best piece of parenting advice I’ll ever give in this blog, so pay attention: Do solo trips with your kids. Whether camping, or to a city or another country or whatever, make the time and do it. Many of my best memories to date with all 3 kids are from such trips, and hopefully, in later years, some of their best memories of me will come from the same trips. (My best childhood memories of my father were from the summer of 1972, when we camped together for 2 weeks in the Maine woods while building a cabin*.)

*He- and a friend- “built”. I fetched stuff, ran errands, played in the woods and swam in the lake.

Twin B is also smart. A couple years ago we had the Trifecta tested for a “gifted*” program in our local school system**. Twin B knocked it out of the park, scoring highest of the 3. She’s observant in a way the boys aren’t, noticing things concerning the behavior and social dynamics of others that her brothers (or often her parents) don’t pick up on.

*I hate the term “gifted.” “Gifted” sounds you got a Wii or a pony for Christmas. Why can’t we just say “smart”?

**2 out of 3 qualified. We elected not to enroll either in the program, which is the subject of a long, complex (and probably controversial) tangent about the merits of “gifted” programs that I may work into a future post.

She’s also the child who looks (in complexion at least) most like me. All of us probably wonder at some point or another what we would look like, or who we might be, had we been born the opposite sex. When I look at Twin B I see a hint of that what-if-me.

AS is my oldest friend. Not “oldest” as in really old*, but as in been friends for a long time. We met sophomore year in college**, when we were partners in EE lab. Neither of us were great students, but we eeked out degrees and hired on at the same company. We worked and roomed together for a couple of years before each moving on and out to cohabit with our respective girlfriends.

*That would be OCRick, who claims he is 63, but is cranky enough to be 80. My theory is that sometime in the last 20 years he swam in a pool containing some of those rejuvenating alien pods, like in the movie Cocoon.

**Yes, that’s right- my oldest/longest-standing friend is from sophomore year of college. I don’t keep in touch with any high-school classmates or childhood friends. And what’s more, AS is the only college classmate I regularly keep in touch with. No, I didn’t assume a new identity, enter witness-protection, find/lose Jesus, go to prison, have a sex change or anything like that. I’m just not very good at keeping in touch for, well, the sake of keeping in touch. Geography might have a bit to do with it; I live 2,500 miles from where I grew up. But mostly it’s just me. I don’t really have a good excuse***.

***When I think about this too long, I’m oddly reminded of a passage from the Silmarillion, right after the Noldor make landfall in Middle Earth: “But when they were landed, Maedhros, the eldest of his sons… spoke to Feanor, saying: ‘Now what ships and rowers will you spare to return, and whom shall they bear hither first?...’ Then Feanor laughed as one fey, and cried ‘None and none! What I have left behind I count now no loss…’ Yes, I was a total Tolkien geek. I don’t know why I think of that passage; I don’t actually feel that way about falling out of touch. I guess it just seems like a cool, bad-ass thing to say when you do fall out of touch. BTW, I always thought Feanor was the absolute coolest, most bad-ass character in the whole Tolkien mythology. Selfish,hot-tempered and way problematic, but definitely very cool.

In 1990, we each, separately, left New England and- with our respective girlfriends- moved West- me to Colorado, AS to Arizona. Since then, though we’ve never again lived in the same place, our lives have moved oddly in parallel, and we’ve met up once or twice a year for desert camping/backpacking trips.

Each of us moved West with, and subsequently married, our New England girlfriends, both of whom eventually turned out to be highly problematic and completely batshit-crazy, and from whom we were each divorced a few years later, each of us (thankfully) childless. AS remained in Arizona, I moved to Utah, and we each remarried, within a year of one another, each of us to women we’d known for years as friends. And in the summer of 2001 we each had daughters, whom we both subsequently took out on daddy-daughter camping trips. So it seemed right that we do such a trip together.

Man, this is a long introduction. Even I’m getting bored. Let’s get going already.

Great idea for a trip right? Too bad about the weather. Last week was the wettest week in Phoenix AS could remember. Washes were running, roads were flooded, and the weekend forecast was in the 40’s and low 50’s.

It’s always weird when you go camping in the desert and it rains. Growing up in New England, you imagine that it never rains in the desert. Later on when you grow up and actually move to a desert, you gradually get used to rain (or snow) in a desert, but every once in a while think, “Really? It’s raining? But isn’t this a desert?” Anyway, in “my”* deserts I’ve been rained on many times, and by and large no longer regard it as unusual. But although I’ve done many backcountry trips in the Sonoran Desert, on both sides of the border, I’d never before visited when it was really wet.

*By “my” deserts I mean the Great Basin Desert, or what we Utahns call the “West Desert”, and the Colorado Plateau Semi-Desert- the whole Canyonlands, Four Corners, Redrock area. These are the most accessible deserts to Northern Utah, and I spend plenty of time in each. Botanically these 2 deserts aren’t all that different from one another, though the geology, topography and weather differs quite a bit.

The Mojave, which sticks a “paw” up into Southwest Utah really isn’t “my” desert, but I spend enough time there that it too feels like familiar ground, and there are strong botanical links (like Blackbrush, Cliffrose and Juniper) between it and the Great Basin Desert.

Saturday morning we drove about an hour and a quarter West into the foothills of the Superstition Mountains. The wash we camped along- a wash that AS had passed by and across many, many times and never seen wet in 19 years- was a steady river the entire weekend. The ground was damp and spongy wherever we hiked. For years I’ve read about how plants of the Sonoran Desert adapt their whole lives around these infrequent bonanzas of moisture. Finally I was seeing one.

Everything in the Sonoran is about water. It seems like every plant and animal here has some super-specialized schtick to deal with limited water access, and when it comes to plants, what’s interesting is that different plants use different schticks, and these schticks determine where they grow, and the floral layout of the desert floor itself. Cactus is the most obvious Sonoran plant type, but we’ll save that for last.

The simplest strategy is that of the Ephemerals, such as Desert Paintbrush and Mojave Aster. These plants germinate when it’s wet, grow, reproduce, and die. Next rainy season some number of their seeds germinate, and the cycle is repeated.

A different approach is the Perennial strategy, used by Brittlebush and Ocotillo. These plants “come to life”, greening, leafing and flowering following rains, then dropping their leaves and going dormant through the next dry spell. Ocotillo typically does this 4 or 5 times/year, presenting a whole different perspective of the concept of “season”. Ocotillo BTW is often considered a cactus, but it’s not. It’s part of an order called Ericales, which includes things like Blueberry and Brazil Nut. Ocotillo has one close relative in the Sonoran, wonderfully-freaky Boojum Tree, which unfortunately (for us gringos) occurs only South of the border.

It can sometimes seem like no leaf lasts for long in the Sonoran, but that’s not the case. A fascinating exception is cactus spines, which as we’ll see tomorrow, are actually specialized (and persistent) leaves. But more traditional persistent leaves can of course be found on our old friend Creosote, and- even more impressively- on Jojoba.

Jojoba, Simmondsia chinensis (pic right- behind cholla skeleton) is a knee-to-chest-high shrub scattered across Sonoran hillsides. It’s not particularly impressive or weird-looking, but it stands out in the desert because a) it’s not spiky/ spiny/ thorny (meaning it’s one of the few plants around you could actually crash into and not take a trip to the ER) and b) it has leaves. Real, year-round*, half-decent-sized leaves.

*Under extreme drought conditions Jojoba can drop its leaves, and so is technically drought-deciduous, but this is pretty unusual.

Even if you’re not into desert plants, you might have heard of Jojoba anyway, particularly if you’re a woman. Many, beauty, skincare and shampoo products tout Jojoba oil as an ingredient. Though many of the claimed properties are no doubt overhyped (like with all beauty products, right?) the oil is in fact an excellent moisturizer and carrier, or base, oil for perfumes. The reason for this is that unlike most vegetable oils, which are made up triglycerides, Jojoba oil is comprised of long chain fatty acids linked to fatty alcohols, and is actually chemically more similar to human sebum* and- get this- Sperm Whale oil. Because of this, Jojoba is the second-most commercially valuable native Sonoran Desert plant (after palms), and is farmed not only in North America, but also in places like India, where it’s planted not only for its oil, but to combat desertification.

*Sebum= the stuff produced by your sebaceous glands. In other words, it’s the real thing- the stuff all those moisturizing beauty products are trying to emulate.

In farming Jojoba, care has to be taken to manage the sex of the plants raised. Jojoba is dioecious, meaning that plants are either male or female, but not both*. Naturally Jojoba occurs in a male-female ratio of about 4 or 5 to 1. But since the oil is the product of the seeds, and only females produce seeds, and 1 male can effectively pollinate (more on Jojoba pollination- which is way cool- in a moment) several females, growers try to manage to a 1:5 or so male: female ratio.

*With very rare exceptions in Jojoba’s case.

Jojoba gets weirder and weirder. It’s monotypic, not just at the genus level, but at the family level. It’s in a family, Simmondsiaceae, all by itself. Its leaves are tough and waxy-coated, like Creosote or Bitterbrush, so it loses little water (pic below, right). And interestingly, the leaves stand, for the most part, straight up (pic left). By doing so they optimize their aspect for maximum solar exposure in early morning or late afternoon, when it’s cooler out, and minimize their exposure to the direct noon-day sun.

Jojoba’s wind-pollinated, but what’s cool about this pollination is that it’s not entirely passive; the leaf spacing/ positioning is such that a breeze creates vortexes within the branches that capture passing pollen and swirl it around the female flowers. Interestingly, male and female Jojoba plants tend to have slightly different branch architecture/ morphologies, which is thought to create more internal shade in female plants, which in turn protects developing seeds.

Extra Detail: The logical connection would be that the “female” morphology also lends to optimized pollen wind-vortexes, but I was unable to confirm this in researching this post. I should also mention that the female-male morphology rule is not hard & fast; there are female plants with “male” morphology and vice versa. But in any case, even if the only benefit is seed-shading, it’s a great example of sexual dimorphism in a plant.

What’s really interesting is what’s going on below the ground. Different desert plants have different rooting strategies, and these strategies determine their relative positioning to one another.

After we set up camp, the 4 us crossed the dirt road, away from the running wash, scrambled up the embankment and gradually worked our way up along a series of slopes and ridges. There was no trail to follow, but cross-country travel in the Sonoran is pretty easy- you just have to watch where you step. Though filled with spiky, sharp and spiny things, plants on the Sonoran Desert floor are widely spaced, and it’s easy to find a path. Gradually, at an easy pace, we threaded our way upward, through and around Jojoba, Cholla, Saguaros, Prickly Pear, Desert Broom and Palo Verde, the girls chattering and pointing out funny looking cacti, bunny rabbits* and such the whole while.

*Desert Cottontail, Sylvilagus audubonii), short (and lame) video below. (Voice exclaiming in background = AS’s daughter .) Whenever we spotted wildlife I whipped the camera out of the shoulder-holster and tried to get a shot or video. By the 3^rd or so attempt, AS would start humming the theme to Mutual of Omaha Wild Kingdom.

Yeah, I warned you it was lame. Don’t get all cranky with me if you wasted 11 seconds watching it.

Mesquite, Ironwood (pic left) and Palo Verde for example, are all what are called phreatophytes*, which are plants whose roots extend way, way down into the ground, all the way to the permanent water table. Cacti on the other hand are xerophytes, which are plants that have adapted to survive with only limited or intermittent access to water. Specific xerophytic adaptations of cacti include succulence- or the ability to retain water, and CAM photosynthesis which we looked at last year, and which limits water-loss by keeping stomates (pores) closed during the day.

*Closer to home, Greasewood is a great example of a phreatophyte in the valleys West of Salt Lake. BTW, phreatophyte is one of those words, which- like so many botanical terms- I’ve only read; I’ve never heard it pronounced. In my mind I pronounce it “free-AT-oh-fight”, mainly because “Frito-Fight” sounds silly.

Cacti have shallow roots networks which take advantage of recent rains, sucking up what moisture they can and storing it. The system works well, but in taller, columnar cacti, the shallow roots can be a liability, making them susceptible to toppling. Here’s a shot of the roots of a toppled Saguaro we passed by.

Saguaros are the tallest plants around in the Arizona Sonoran. They grow up over 40 feet tall, live up to 200 years, and can weigh up to 6 tons. Why don’t they have deeper roots?

First off having shallow roots isn’t necessarily a bad thing; the closer to the surface your roots are in the desert, the more of the rain you can catch. But shallow roots help Saguros in another way.

Cacti are divided into two groups- Opuntia and Cereus. Segmented cacti, like Cholla and Prickly Pear (pic right), are Opuntia. Cereus are columnar cacti, like Saguaro, Hedgehog and Barrel*. Up around Phoenix, Saguaro is the only tall Cereus cacti.

*Another difference between the 2 groups are the spines, which I’ll cover tomorrow.

There are other tall Cereus species, but for the most part they’re down in Mexico. Organ Pipe makes it across the border into its namesake national monument, and about 50 Senitas have made it across the border as well, but overwhelmingly these species are found only in Mexico (where they grow like weeds.) The mighty Cardon cactus (up to 75 feet tall), so far as I know*, occurs only in Mexico.

*Wikipedia claims Cardon cactus extends into Southern Arizona, but I’m unaware of any such location and couldn’t confirm.

Saguaro is the outlier, pushing into the very Northern fringes of the Sonoran, and what’s interesting is that it only arrived there within the last few thousand years*. And most of the larger “trees” it encountered when it arrived there- Palo Verde (pic right), Ironwood, Mesquite- are phreatophytes. But Saguaro with its shallow roots, is able to fit in nicely alongside these deep-rooters. Look around next time you’re in the Phoenix area. You’ll almost never see Saguaros clumped together; they’re widely spaced, each staking out a shallow “root-territory.” Yet they frequently grow next to, or even intertwined with, phreatophytic Palo Verde and Mesquite; they don’t compete, by and large, for root “real-estate.”

When you notice this spacing as you walk across open Sonoran Desert, as the 4 of us did behind our campsite Saturday afternoon, it slowly dawns on you that the seemingly random scattering of desert flora isn’t all that random after all; that each bush, shrub, shree and cactus occupies a space in a well-ordered mosaic, a sophisticated living jigsaw puzzle-equilibrium of positioning and hydrology. And when you see hints of that order start to become visible out of the array of plants, the desert somehow becomes beautiful on a whole other level, one you didn’t see before.

*The whole Sonoran desert in Arizona for that matter, in its current range and incarnation, has only come about in the last 10,000 years.

Side Note: Speaking of root strategies, know what plant’s got a really, really cool one? Creosote*, that’s what. No, not just because of the incredible, multi-generational root –clones it forms, spreading in concentric rings across the desert floor and dating back over 10,000 years. Yeah, that’s cool, but what else is really cool, is that it has a 2-tier root architecture, with both a distinct, opportunistic shallow-root network to take advantage of monsoon rains, as well as a deep-reaching phreatophytic network to access the underlying water-table.

Clones, rapid colonization, geographically distinct polyploid races, allelopathic chemical warfare and a cool smell to boot- Creosote has totally got it going on.

*Creosote is so cool, in my next life I am doing a blog just about it and nothing else. It’ll be Way Awesome. You’ll see.

So it was fun to see the desert wet, and to think about how water, and access to water, shapes the form and layout of the desert floor. But none of that was what was really eating at me. No, what was really on my mind was the same thing that’s always on my mind on off-trail Sonoran hikes: Why is everything so damn sharp and spiky?

Next Up: Spikes, Spines and Thorns