California Oaks and Acorns

With over 600 species of oak trees on our planet, this venerable tree surrounds many of us. This time of year we watch the seasonal changes, but every season is a joy with oak trees.

Oak trees live only in the Northern Hemisphere. They belong to the genus Quercus, meaning “fine tree” in Latin.

More info: Oak Wikipedia

Here in Northern California, the oaks have endured the summer drought with stoic strength. They stretch their mighty roots deep into the earth for moisture when the rest of the landscape is parched.

We have approximately 20 species in California, the Bay Area has eight or nine. See penultimate photo. Oak woodlands cover approximately 8.8 million acres of California (Bay Nature, Spr. 2022).

Everywhere I go in this great state, I am always studying the oak trees, trying to determine which species I am fortunate to have the pleasure of meeting.

I look closely at the bark and leaves, the shape of the tree, take note of the location.

Acorns are also helpful identifying tools, if there are any on the tree. Phone apps for identifying species help, too.

But identifying an oak species can be tricky, I have found, because they hybridize. So I try not to get too involved with identification studies…I am not presenting a dissertation, it’s simply a walk among friends.

More important than identification is taking note of the grand queen I am in the presence of, and what she has to offer.

An early springtime stroll through oak woodlands reveals lichen-covered and leafless oaks, and winter rains still saturating the hillsides.

Later in spring the lupine wildflowers emerge and the trees are budding.

Winter brings a bouquet of moss and lichen to every tree; many are draped with lace lichen, the State Lichen.

This brown creeper, below, was busy hunting insects nestled in the lichen and moss.

Oaks are magnets for all sorts of wildlife.

This week I had the pleasure of a great horned owl serenade in the oaks out back…a calm duet in the middle of the night.

Autumn is a great time for watching creatures pluck the acorns and whisk them off to their special hiding places in preparation for inclement days.

Acorn woodpeckers, named for their expert reign over oak trees, can often be seen snatching the acorns, squawking loudly, calling waka-waka-waka. They robustly tug and remove the nut and fly off in a flurry of black and white to deposit it.

A granary is a designated place acorn woodpeckers have chosen for storing their precious acorn supply. Usually a granary is a dead tree (not necessarily an oak), but the birds also use utility poles, fence posts, wooden buildings. As colonial birds, they rely on each other to protect their wares.

Over the years they have created these holes for storing acorns.

You can see (below) the holes that are stuffed with tan-colored acorns.

Over time a granary acorn will dry out and get smaller, so the acorn woodpeckers relocate it to a different hole where it fits more snugly and safely.

Every species of woodpecker visits the oak trees, not just acorn woodpeckers.

And both our jay species do, too. Western scrub-jay and Steller’s jay. When the acorns are ready, the jays doggedly gather acorns all day long.

Equally as fun is witnessing the jays months later retrieving the buried acorns from the ground or shrubbery.

Nuthatches get their name from jamming large nuts and acorns into tree bark, then whacking them with their sharp bill to “hatch” out the seed of the nut.

Squirrels of course take to the nuts. We expect this of tree squirrels, but even so-called ground squirrels scramble about in the leaves at acorn time. Apparently the ground squirrels throw caution to the wind, scurrying about in the oak tree instead of on the ground. More than once I have witnessed the ground squirrel falter and fall out of the tree, plop on the ground. They don’t seem to be hurt and in fact go right back up the trunk.

Here you can see a trio of acorns (lower right) that the ground squirrel is precariously heading toward.

Long ago acorns were prized by human indigenous populations too. There is, however, a lot of work to preparing an acorn for human consumption, due to the nut’s tannins.

More info: Acorn Wikipedia

After the acorn celebration is over, in a few months the deciduous oaks will be leafless, giving us a clean view of the gnarly limbs and multiple trunks.

They close down and rest for a season of cold days and nights.

When spring arrives, the tree produces catkins, its flowers. In the black oak (Quercus kelloggii), photo below, you can see hanging filaments dotted with tiny red balls–those are the catkins.

The leaves start out red.

As the season progresses, the leaves get bigger and turn from red to lime green. Then as the California sunshine intensifies, the lime green leaves turn darker green and get tougher, leathery.

Our old black oak tree was very entertaining every spring when birds arrived to pluck juicy caterpillars rolled up in the new leaves. It was great for the tree too, removing pests.

With each new season the oaks change and we are reminded by this lovely being how wise and wonderful life on earth can be.

Written by Jet Eliot.

Photos by Athena Alexander.

Great reference guide for oaks: The Sibley Guide to Trees (2009) by David A. Sibley


81 thoughts on “California Oaks and Acorns

  1. This was really interesting, Jet! I didn’t know that oaks could hybridize. I also wasn’t aware that certain birds store acorns in tree holes. I can see how it would be very entertaining to watch that all unfold. I’ll be paying much more attention next time I encounter an oak tree.

    • I was thrilled to see you found the oak essay interesting and that it convinced you to watch oak trees more, Diana. The oaks are really a superb presence on our planet and we’re so lucky to have them. My warmest thanks for your lovely visit and comment.

  2. You might want to double check your association of the catkins with developing leaves. As far as I’ve known, catkins on a variety of trees are their flowers. When I looked up the California Black Oak, I found that their “small male flowers are clustered on drooping catkins while female flowers are single or clustered.” Because the catkins emerge from the leaf axils, new leaves and catkins are easy to confuse. An Oregon State site says, “Separate male and female flowers are borne on the same plant. The greenish-red male flowers arise from leaf axils of the previous year…female flowers emerge from leaf axils of the current year.”

    That’s a whole lot of complicated timing going on! Something that surprised me in this great post was your mention of a Sibley guide to trees. I’m so accustomed to equating Sibley and birds, I had no idea that other topics had been covered in his books. It’s off to find a copy!

  3. Wonderful post! I especially loved the photos you were able to get of the woodpeckers storing their acorns. We have a large valley oak just outside the house windows and it provides for so many life forms! It’s a bird watching spot in itself. Even the swallows have an elbow of a large branch reserved for their annual time in residence.

    • How fortunate you have a valley oak right outside your windows, Lisa. I can imagine how lively the tree must be and enjoyed your descriptions. Many thanks for your visit and comment, much appreciated.

  4. Fabulous article Jet. 👍👍 It prompts me to mention that we have quite a large walnut tree in our garden and there were hundreds of walnuts hanging off the branches. We were hoping they would ripen for us to collect, but we went away for a week and, when we got back, every single one was gone. The squirrels must have been extremely busy. I’ve no idea where they took them, but each was larger than a juicy plum.

    • Oh wow. I loved your walnut story, Mike. You’re probably still getting to know your new home and the seasons, and to discover you had all those large walnuts was great, and then the next discovery is that they all vanished after a week away. Nature has a way of playing with us, eh? Thanks so much for your visit today and for sharing your walnut story. Cheers to you.

  5. What a wonderful post! Loved learning about the granary stores – what a sight, and such industry from the birds…
    To me, oaks are so reliable, for want of a better word. Familiar from childhood perhaps, and their gnarly presence is a comfort – and busy habitat- to so many.
    Thanks, Jet, great stuff!

    • I’m with you, pc, there is something reliable and wonderful about oak trees. I liked hearing about the oaks you had in your English childhood. My warmest thanks and cheers to you for a happy weekend ahead.

  6. I have a huge oak tree, at the side of my home in Ocala, FL. I still don’t know what type is it. You can see the Spanish moss hanging from it. Many people, love the tree. My home is in a corner and it looks majestic and enormous. I love trees!I liked your post about oaks in California. Thank you, my friend. 🙂

    • How very wonderful that your new property in Ocala has a huge oak tree, H.J. It’ll be a fun mystery for you to solve, learning what kind of oak it is. I’m happy you and your family have found a new and beautiful place to live. Many thanks, H.J., always a delight to “see” you.

  7. So much great detail in this post about your oaks and the critters that feed on their acorns. Oaks make a mockery of the concept of species. When I studied dendrology, I learned that essentially there are red oaks and white oaks. Differentiation is based much on the environment where the trees grow. I never thought of the nuthatch name in that way before – but of course! We have pinyon jays hanging around here now. They’ve been after all our pinyon cones, but I think they and the scrub jays are going for acorns, too. The rock squirrels and chipmunks get in the act, too.

    • Thanks so much for your comment, Eilene, I enjoyed hearing about your pinyon jays and scrub jays, rock squirrels and chipmunks, as well as your studies of the red oaks and white oaks. I’m happy you stopped by and enjoyed the oaks and acorns post.

  8. Ya gotta love oak trees. I think they’re wonderful and always magnificent. Our white oak trees would produce a bumper crop every 3 years. The deer loved them and walking in the yard was very crunchy. The acorns sure do keep the Acorn woodpeckers busy.

    • Hi Bill, I, too, think the oaks are wonderful and magnificent, and I appreciated hearing about your white oaks and the acorns. Thanks so much for your visit. I thought of you when I composed this post, remembering how much you enjoyed our old black oak tree. Cheers and thanks.

  9. I really enjoyed this. I’ve never lived anywhere they were prominent. There was oak brush in Utah where my father was from, and a few domestic ones in a small area of downtown Boise. I did name a character Quercus Alba in a book I finished, but haven’t published yet.

  10. I loved this Oak Tree study! I love them. My daughter’s property in Tuolumne Co. has lots and lots of Oak trees which I enjoy. This week while there I saw many Acorn Woodpeckers busily collecting and storing their harvest. Two are busy trying to stash them in their homes roof!! They’re looking for deterrents hoping to keep them in the trees.

    I haven’t identified the type(s) on her property either but, think they must Black Oaks since many places around them are named for the Black Oak Tree.

    • I enjoyed hearing about your daughter’s Tuolumne Co. property, Deborah, and the oaks and acorns and the swirl of autumnal activity they produce. Thanks so much for your lovely comment today.

  11. I always thought we had Valley Oaks but according to your chart, we have Interior Oaks! They grow like crazy. I have to scour the yard for “volunteers” all the time otherwise they sprout like weeds!

    • It was great hearing that you were able to identify your Interior Live Oaks, Jan. You probably also have valley oaks in the neighborhood somewhere too. Valley oaks are the biggest of all of Calif. oaks and I’ve seen them all over Walnut Creek (as well as interior live oaks), so you probably have them in O, too. Loved hearing from you about your oaks, thanks so much for your visit.

  12. A beautiful post, Jet. Like you, I am a lover of oak trees. I identified closely with this statement: “I am not presenting a dissertation, it’s simply a walk among friends.” Thanks for the work that you put into this post and for taking us along on your walk. –Curt

    • Your comment was very kind, Curt, thanks so much. Spending many years in the U.S. west, as you and I both have, has brought us happily close to oaks. How wonderful that is. Thanks very much for your visit.

      • We’ve moved to the east, now Jet. Our kids are providing a base camp as we approach wandering full-time. I was amused to find our son-in-law busily gathering and growing acorns so he can line the front to his property with oaks. 🙂

  13. Wonderful description of the mighty oak and its acorns. I had no idea there were so many varieties of these impressive trees. I loved how you took us on a time-lapse journey through an oak’s annual changes. I also loved how you described and explained the interconnection with flora and fauna related to the oak. Well researched and the photos are stunning!

  14. Such an interesting and enjoyable post, as always. We have several oaks (not sure what kind) in our back yard and they seem to be the last ones to let go of their leaves in fall. We also have maples which drop leaves early so we have two raking sessions coming up this season. I loved reading the background and cycles of these trees I love.

  15. Ah, the mighty (and stoic) oak. I loved the oak trees near us when we lived in Marin, and now here in the Boston area, the oaks are forthright, solid, and magnificent. The acorns are plentiful, and when the squirrels start throwing them on the ground (like just around now) and then scurrying and picking them up to bury them, I know fall is upon us. I DIDN’T know about woodpeckers and acorns! We have dozens of woodpecker families in our neighborhood who love our suet feeder. In fact, if the suet is gone, one of the ‘head’ woodpeckers knocks on our window until we replace a new one. (Truly). But I’m going to check out the acorns deposited in nearby oak trees now. Thanks for the fabulous info, Jet.

    • Great to hear about your experiences with oaks in Calif. and Mass., Pam. I looked at a range map of the acorn woodpecker and found that you do not have this species of woodpecker in MA, so you will not see their behavior. But I sure did enjoy hearing about the cheeky woodpecker at your house who taps on the window when it’s time for a new suet cake. Brought a smile to my face. My warmest thanks and cheers to you and autumn.

      • Aha! So, no hidden acorns in our oaks. But the squirrels (or chipmunks?) hide acorns in our outside flower planters. We wake up in the morning to find dirt all over our front porch. 🙂

  16. Awesome shots and great information. I particularly enjoyed the shots of the amazing Acorn Woodpecker, a species that I have always wanted to see. The warbler was a nice bonus. Like so many other readers, I am shocked by the number of different types of oaks that you have in your area.

    • I am happy you enjoyed the oak post, Mike. I enjoyed composing it and gathering up Athena’s photos from years of oak admiration. That warbler came to our black oak a few years back one spring and she was quick with her camera. Then when we recently moved, we spotted those dead tree granaries across the street longingly even before we bought the house. So when I was composing the oak post this month, we were out in the street photographing it, and were fortunate that the neighbors were home and welcomed us into their back yard to get closer. They liked the trees too and all the acorn woodpecker activity. Many thanks, Mike.

  17. Hi Jet, One of my favorite things is seeing California Oaks dotting the hillsides and now, thanks to you, I now know how varied the types are. The gnarly, beautifully shaped oaks that are so prevalent in the Bay Area (that I’m obsessed with photographing in winter) I thought were CA Live Oaks, but maybe they are Valley Oaks? Love all the info you’ve provided, as always. Thanks for enlightening me! 🙂

    • I’m delighted you enjoyed the oak post, Jane. You and I share a love for those Bay Area oaks. Since there are eight different species here, and hybrids, it’s hard for me to say what you were seeing. But my guess is you were probably seeing one of the Live Oak species, as you originally thought. They keep their leaves all year long and are prevalent. Many thanks for your visit and kind words.

  18. ​The oak trees of California simply have so much character. Can’t think of a better way to put it. One of my favorite photos from my early days in the Sierra foothills below Lake Tahoe was one of those lone oaks standing sentinel in a field. They seem to embody patience and perseverance. ​These days it seems the only oak we have is the Tan Oak and there’s some disease spreading and decimating them. Sigh. 🥴

    • I agree with you, Gunta, the Calif. oaks do have much character. I liked how you so clearly remembered that lone oak many years ago from your time in the Sierra foothills…they are indeed memorable. I’m sorry to hear about the tan oaks in OR. I have read about the sudden oak disease of which you speak. It takes them quickly…a difficult situation. Sending you warm wishes, my friend.

    • I really appreciated hearing about your oaks in the UK, Ed. I think it’s interesting how some years have more acorns than others. In fact in researching for this post I discovered there’s a whole science to it called “masting.” I’m glad you enjoyed the post, thanks so much for your visit and comment.

  19. Long live the oaks! We are blessed with a variety of oaks in and around our woods – next to the hedge/osage not sure there is a more hardy tree out there once they get their roots sunk deep enough. I wish I could convince some of your Acorn WPs to trek out here and enjoy them ha. Another entertaining post.

    • Hi Brian. I liked your opening comment here: “Long live the oaks!” Aren’t they so incredible? We went through a really harsh heat wave last month and they just stood tall and dug their roots in. I’m glad to hear you have oaks to enjoy, too. Thanks for your kind words.

  20. Ah, I can finally relate to the Acorn Woodpecker behavior having now seen one in person. Thanks for the pictures of the granary – always a bonus when you can see the fruits of their behavior. A lot wiser now, Appreciate it Jet.

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