Is It True That Oaks Survive Fire, and How?

Ah oaks. Yes, they do usually survive most fires. And thank goodness—they are among
my favorite trees. Oaks are not the oldest, widest, largest, or tallest trees, but wherever they
occur, they tend to dominate both in the forest and in scrub land. Oaks cover 1/3 of California’s
33,000,000 acres of forest. That is a lot of acorns!

The genus for oaks is Quercus and is thought to be of Celtic origin meaning “beautiful tree”.
Agreed! The Romans in Ancient Britain must have incorporated that local name into their Latin
language. About 500 species are widespread throughout the temperate northern regions and
range as far south as the equator. But there are no oaks in the Southern Hemisphere. We have
about 22 species in California and at least 10 in the Bay Area. The common tan bark oak is
closely related to Quercus but falls into a different, more primitive genus, Lithocarpus.
The Spaniards noted the difference between evergreen and deciduous oaks. The former they
called encino and the latter, robles. Both thrive in our Mediterranean climate. Due to our mild
winters, encinos do not require complete dormancy to survive the cold and their evergreen leaves
persist for years. Another main attribute of the Mediterranean climate And then there are the
regularly recurring fires of a Mediterranean climate.

In addition to fires started by lightening, Native Californians have been using fire as a
management tool for perhaps 10,000 years. Fire clears out the undergrowth, creating improved
habitat for deer and it facilitates the gathering of acorns—the most important food source for
most California tribes. The fires also free nutrients into the soil, enhancing growing conditions
for the trees. These anthropogenic fires were usually of low intensity and fairly frequent so that
there was not a huge buildup of combustible material, nor much lasting damage to the trees.
As long as fires are not intense infernos, most oaks will survive. They have very thick barks that
are resistant to heat and safeguards the vital cambium layer. Evidence suggests that fire scars
may even help protect the trees from invasive fungus. How? Some oaks develop tyloses. These
are fast growing cells that effectively block off the damaged parts and isolate them. And even if
all the leaves are burned off in a spring fire, they can totally regrow the leaves by summer’s end.
Occasionally a tree is burned completely to the ground, but with the extensive root system still
intact. The next year multiple trunks emerge like a flock of woody Phoenixes rising from the

Scrub jays and western gray squirrels are continually caching acorns throughout my yard in
downtown Santa Rosa. Thanks to these widespread critters there’s always a huge reservoir of
potential oak trees below the surface protected from the heat of fires. Fortunately, they forget to
eat many of them, so the seeds are ready and waiting to sprout when the conditions are ideal. An
extensive study in the Sierra foothills covering the last 200 years, showed a clear correlation
between periodic fires and successful establishment of young blue oak saplings.
The Druids were the priestly class of the ancient Celts. Druid literally means the “knower of the
oaks.” In the last hundred years or so there has been a resurgence of tree huggers, regardless of
class. Count me as one of them, Alma! Count me in as a student and a stewarder of these
beautiful trees.

How do Birds Know Which Way to Migrate?

Humans have been observing and wondering about bird movements since forever.
The ancient Greek poet Homer described the Trojan army as being like cranes that
“flee from the coming winter and sudden rain.” And from the prophet Jeremiah: “Yea
the stork in heaven knoweth her appointed times.” Well and good, but how in
heaven’s name do the birds knoweth the proper time and how the heck do they
findeth their way? Much progress has been made by ornithologists in the last 60-or-
so years in beginning to answer those questions. Not unexpectedly, the answers are
complex and multifold, the research ongoing.

You probably know that a large portion of North American birds—75 percent of the
650 species that nest here—migrate, or move from breeding grounds to wintering
grounds and back. (That’s different from dispersal, when a young bird fledges and
leaves the nest for new territory, and irruption, when birds are forced out of their
normal feeding areas due to lack of available food.) But did you know that migration
is mostly a northern hemisphere phenomenon? Among the reasons for that: There is
simply more land available in the northern expanses of the earth. Just look at a globe
to confirm this.

We know birds are able to both orient (use an internal compass to determine
direction of travel) and navigate (find a specific location using that internal
compass). And we know that they, like humans with our maps and GPS and stopping
to ask strangers for directions, use multiple systems to find their way.
First, in the 1950s, scientists discovered that birds use a so-called “sun compass” to
tell direction, and it works in conjunction with their internal clock. Birds
“understand” that at 3 p.m. the sun is in a different place than at 8 a.m. and make
adjustments. They are also sensitive to polarized light, which means even on partly
overcast days their sun compass works. A well-known study by Stephen Emlen, a
behavioral ecology professor at Cornell University, observed captive indigo buntings
to prove that migrating birds rely on a “star compass” by night, based on the North
Star. And finally, in the 1960s, scientists established the existence of a kind of inner
magnetic compass, by altering the magnetic polarity that captive migrating birds
were exposed to; the direction of travel changed accordingly.

Now, exciting new research reveals the possible “how” of that latter finding. It seems
that birds’ eyes feature specialized cells called cryptochromes, some of which
undergo reactions when exposed to light, different chemical reactions, depending on
the influence of the earth’s magnetic field—meaning that birds may essentially be
able to see magnetism. Think about that for a second. What is actually happening
there on the cellular level is amazingly cool. Then, consider: how in the world did
this process evolve? That ability, that chemical process, that particular reactive
cryptochrome, seems to have enabled some birds to reproduce more successfully
than others, and here we are. That’s just wonderful.

Plenty of other animals are also magnetic navigators: newts, sea turtles, fish, mole
rats, deer, dogs. (There’s even some research indicating humans can sense changes
in magnetic fields—although I’ve certainly known plenty of people in my time who
couldn’t magnetically navigate their way out of a shoebox.) But once a bird has the
general travel direction, other factors come into play that fine-tune the route. Some
birds use geographic features like large rivers, mountains, or ocean shores to chart
their course. There are also magnetic anomalies birds may “recognize” as intrinsic
earth features. For instance, homing pigeons use landmarks like buildings to help
find the way back to their domicile. A few species, like storm petrels, may even use
smell to find their home burrows.

When I lived in West Marin years ago, a barn swallow made a nest above our
kitchen door for three years running. When the bird family departed in late summer,
they presumably flew all the way to Argentina to enjoy the insects in the vernal
pampas. And then the same pair returned to our back porch. That’s a very long trip

What’s It Like Inside a Woodrat Nest?

Woodrats, pack rats, and trade rats are all common names for the same remarkable rodent genus, Neotoma. Our local species, the dusky-footed woodrat (Neotoma fuscipes), has a nice multicolor coat—unlike the nasty nonnative Norway and black rats, all too common in urban areas. It’s also extremely cute, with big Mickey Mouse ears and a lovely, lightly fuzzy tail. Yes, I am biased.

If you’re a hiker, it’s hard not to notice their strikingly large nests, which can be three to six feet high, up to eight feet across—approaching the size of a Volkswagen bug or my stack of unread New Yorkers—and often built right on the ground. Like us humans, woodrats have very particular requirements for their homes. They don’t like light (not even moonlight) and so prefer densely shaded areas, especially near water. But they also need to keep their fur dry for good health. Not too dry or too wet. Goldilocks with whiskers!

A dusky-footed woodrat emerges from its hole. (Photo by Jon Klein)

Woodrats are sometimes called pack rats because they love to collect and store various kinds of junk, much like my former mother-in-law did. And often when they are carrying an item and encounter another prize they consider more enticing, they’ll put down what they’re carrying and abscond with the new treasure—hence the other common name, trade rat. (They are especially attracted to shiny objects…again like my mother-in-law.) Folks living near these critters have reported missing shoes, lace curtains, crackers, soap, wallpaper, and even gum wrappers. Why someone missed gum wrappers is unclear to me.

Woodrat nests are especially easy to find in the winter, after the understory shrubs have dropped their leaves. Nearly every coast live oak forest or willow thicket hosts a few nests. You might find anywhere from 10 to 100 other nests in close proximity, since woodrats thrive in extended colonies of related females. During the winter and spring breeding season, male woodrats move through these nests searching for females in heat. No messing around for these rats; they are monogamous, at least for the time it takes to raise a brood.

What might seem like a haphazard assemblage of branches, stems, leaves, bones, shredded bark, grass, and basically whatever material is easily available (including wire, glass, and old shoes) belies a very complicated interior design. First, woodrats are fastidious housekeepers, with separate areas for pooping, which they clean out regularly. Nests tend to have many tunnels, entrances, and exits. Woodrats build specific chambers for sleeping, giving birth, and nursing and often incorporate their tchotchke collections into their homes as decoration of sorts. They maintain several pantries for stored food, including a room for aging poisonous toyon leaves. They are the rare mammals that can eat these leaves, which contain toxic-level cyanide compounds; their leaching rooms help break down those toxins to make the leaves edible.

How do Marine Mammals Sleep?

Sleep is incredibly important to higher vertebrates such as reptiles, birds, and mammals. Continued disruption of sleep—as the parents of newborns and the CIA know well—is a torture technique. And while the function of sleep is not totally understood, we do know that it’s absolutely vital to the health of animals.

During a whale-watching trip years ago out of Half Moon Bay, at around 3:30 in the afternoon—just about the time I like to take a nap—I saw a very light blow, or exhalation, from a whale. As we approached, we saw that the whale wasn’t swimming. We turned off our engine and drifted near the stationary whale for over an hour. We watched silently as the animal slowly sank beneath the surface, disappearing for 90 seconds, resurfaced in exactly the same location, took a very light breath, and then sank back down—over and over. My conclusion was that the animal was asleep. But breathing is not an involuntary autonomic response in whales as it is in terrestrial animals. How can you sleep if you’re a voluntary breather like this whale?

Studies of both captive and wild cetaceans have revealed a most fascinating adaptation: Half the brain appears to stay awake while the other hemisphere drops into what we call slow-wave sleep, or deep sleep. There are basically two different kinds of sleep as measured by electrical activity in the brain—REM (rapid eye movement) sleep and non-REM sleep. In non-REM sleep there are three stages, each characterized by decreasing frequency of electrical impulses. During stage III (slow-wave sleep), memories are consolidated into the neural network, and essential repair to bodily systems takes place.

Studies on captive bottlenose dolphins show that each side of the brain gets a total of about four hours of “sleep” in short stints as the opportunity arises over 24 hours. Half of the brain nods off and the opposite eye closes while the other wakes up and helps the animal survive. This is called unihemispheric slow-wave sleep or USWS. Survive how? This evolutionary transformation allows the animal to safely breathe, consolidate memories, do essential bodily repair, interact with other members of its social group and stay cognizant of potential dangers like predators or large vessels approaching.

But what about pinnipeds—true seals (such as harbor seals) and eared seals (such as California sea lions) that can be found sleeping on land but spend many months at a time in the open ocean? Even though DNA analysis indicates that these two mammalian lineages share a common ancestor, only the eared seals exhibit USWS. But for some reason that remains unclear, true seals do not undergo USWS but are nonetheless very successful at getting the necessary “sleep” in their watery world through bilateral slow-wave sleep and holding their breath. An elephant seal, for example, can hold its breath for more than an hour. Other aquatic mammals, such as the Amazonian manatee, also have been shown to have USWS.

REM sleep occurs simultaneously in both hemispheres and is the final stage during the sleep cycle characterized by dream activity, increased breathing and respiratory rate. The electrical activity of the animal’s brain during REM is quite similar to that when it is awake. While pinnipeds experience something like REM while on land, it turns out cetaceans do not go through REM sleep, so I reckon they don’t dream.

It’s 3:30 pm—time for that nap essential to my health. At least that’s my story and I’m sticking to it.


For Bay Nature Magazine–a wonderful publication.

The Great American Exchange

For millions of years, North and South America existed in geographic isolation — there was no Central America. North America began as part of the supercontinent Laurasia — that is basically all the land in the northern hemisphere. And South America began as part of another huge continent, which included Australia and Antarctica. In these separate regions plants and animals evolved in “splendid isolation” as Alfred Wallace first described it in the 1800s.

But beginning around three million years ago, volcanic activity created the Isthmus of Panama. The land that arose “suddenly” connected these two huge landmasses and caused one of the most remarkable events in the history of our planet. Abruptly there was a gigantic swap of fauna from one region to another, today known by biologists as the Great American Exchange. Camels, native to North America, headed south and evolved into llamas and vicunas. Deer, tapirs, cougars, skunks and foxes also went south into new territory and radiated out into a large number of species. Overall the exchange between north and south was quite uneven. The North American species basically out-competed, dominated and caused the extinction of many of South America’s animals.

On the contrary, only a few species from South America succeeded in conquering the Northern Hemisphere. The modern descendants of these southern mammals are armadillos, porcupines and opossums. There are no armadillos here but porcupines are a native California critter. The opossums we see in the Bay Area were allegedly introduced into San Jose in 1910. Goodness knows why — perhaps Granny was missing some of that possum stew she fondly remembered from back home in ‘Kentuckee’. At any rate these marsupial mammals have landed fully in California and thriving in our suburbs.

So last week when I passed several flattened on the road, I was reminded of those Grateful Dead lyrics — “what a long, strange trip it’s been” at least for those possums.