How Does the Acorn Get from Here to There? – Scrub Jays and Oak Trees

With a few exceptions trees in the Oak genus (Quercus) are easily, if not immediately, recognizable.  There are approximately 600 species in the genus divided into two sub-genera.  Oaks are found in North and South America, Europe, North Africa, and Asia.  The oaks in Asia are in the sub-genera, the Ring-Cupped Oaks (Cyclobalanopsis), whereas oaks in the rest of the world are members of the Quercus sub-genera.

Oaks have complicated relationships with a number of other species ranging from symbiotic fungus to parasitic wasps to humans.  Oaks feature in our mythology, we use the bark of Quercus suber, Cork Oak, to make stoppers for wine and for soft flooring, we make furniture and barrels from some species of oak, we made cart and early car axles from particularity strong species, they make excellent firewood, and they are fun to climb.

Climbing a Coast Live Oak (Quercus agrifolia) when I was little

Oaks also make acorns.  Sometimes, particularly when mast fruiting, oaks produce enormous quantities of acorns.  Most of these acorns are eaten by animals; insects, humans, pigs, squirrels, birds, and a host of other animals.  The survival and reseeding rate for acorns is low, but oak trees tend to be long-lived, some reaching ages of 500 years or more.  In the absence of other factors this low seedling success rate is not an issue as the tree produces thousands of acorns each year for hundreds of years.  Some seeds are bound to survive and turn into new trees.

Oaks have a particular problem.  Their seeds (acorns) are large.

Coast Live Oak (Quercus agrifolia) acorns

By themselves the trees can only drop the acorns under their own drip-line, in the shade where they will not sprout.  How does the tree send its seeds to a new place where they can sprout and are not left in a dense mat of easily found and eaten food?

Plants, being clever and manipulative in their slow vegetative manner, have all manner of methods for getting animals to carry their seeds far and wide.  Oaks harness many species to do this work, bribing them with the highly nutritious seeds they produce.  Across much of North America scrub and blue jays are put to work distributing acorns across the landscape.

Western Scrub Jay (Aphelocoma californica) in the Santa Monica Mountains – possibly Belding’s Scrub Jay (Aphelocoma californica obscura)

Meet the Western Scrub Jay (Aphelocoma californica), also known as the California Scrub Jay, and sometimes known as, “That damned bird!”  It is a mid-sized bird, perhaps a foot long including tail, loud, strong, clever, and imperious.  Like all jays it is in the Crow family (Corvidae), one of, if not the, smartest of bird types.  Corvids are renowned for their problem solving abilities and feats of memorization.  Scrub jays are no exception.

When the acorns are ripe jays congregate on the trees, grab as many acorns as they can, and fly off to stash them for future use.

Scrub Jay carrying acorns to hide for lean times

Each bird seems able to carry 3 or 4 acorns at a time, in the picture above there are two in the jay’s beak and at least one more in its crop.

Jays will carry acorns up to a mile and a half, hiding them in widely distributed caches of 1-3 acorns per cache.  The bird memorizes the locations of each cache, that of any other caches it sees other birds store, and will move its own caches if it knows it has been observed making its own cache.  Some of these caches will be forgotten and in some of those the seeds will sprout.

One bird doesn’t seem like it would make much of an impact, but one must recognize both the diligence of each bird and the number of birds engaged in this activity.

Scrub Jays harvesting acorns (@ 40 photographs taken over @ 10 minutes)

The photo above is a compilation of about 40 photographs taken over roughly 10 minutes.  This level of activity has been constant on this tree throughout the day over the past 2 or 3 weeks.  The scale of the endeavor starts to become apparent.  Beneath the tree ground squirrels and gray squirrels gather seeds from the ground to add to their own larders as well.

The oak tree has effectively expanded its dispersal distance from a few feet to over a mile.  Not only that, the oak tree has found a way to have its seeds hidden in safe locations and planted in the ground.  Only a small proportion of the acorns will survive to make new trees, but over the 350 year expected life-span of this particular tree it is not unreasonable that several hundred acorns will survive to produce trees that will live long enough to produce seeds of their own.

Scrub Jay enjoying the sun

+++ Cathy commented that any discussion of oak trees in California is incomplete if Acorn Woodpeckers (Melanerpes formicivorus) are not included.  They don’t live where I am at the moment, but last week I was up in my old stomping grounds and visited one of my favorite grainery trees.  Grainery trees are where these communal woodpeckers store and dry their collected acorns.  This particular tree is an ancient, wind-blasted Douglas Fir atop Mt Tamalpais, has a nearly 4 foot diameter, has been lightening struck numerous times, and sits amidst a copse of large moss enshrouded oak trees.

Old grainery trees will be used by many generations of these little woodpeckers and the trees look like an art project .

In any event, here is a photo of part of a grainery.+++

Acorn Woodpeckers (Melanerpes formicivorus) use all surfaces of a tree to make their larders. They will use fence-posts and the sides of barns as well.

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As a final note, in many areas, but in California in particular, oaks of all species are severely imperiled.  Oak woodlands are often considered to be the most important ecosystem in the region, but they have been subject to a number of stresses.  Oaks have been extensively cleared for orchards, vineyards, farmland, and urban use.  Saplings are eaten by cattle in range-lands, non-native feral pigs sniff out and eat all the acorns they can find, sometimes damaging tree roots in the process, and an ill-considered introduction of turkeys to the state by Fish & Wildlife to raise hunting revenue has led to even more acorns consumed by these overly prolific birds.

On top of all this, Phytophthora ramorum, a pathogen in the fungus-like family of water-molds, was accidentally introduced to the state via exotic ornamental plants and is causing wide-spread devastation.  This is commonly called Sudden Oak Death Syndrome and foresters strongly recommend not transporting oak firewood and washing cutting tools and boots when moving between oak growing regions.

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A Brief Stopover in the Santa Monica Mountains

I am back on the West Coast of the US for a few weeks before I fly off into tomorrow sometime in November.  The specific part of the west coast I am in is the Santa Monica Mountains, a rugged stretch of steep sided hills perched over the Pacific Ocean covered with blanket of dense chaparral.

Evening sunbeams in Topanga

The precipitous, heavily weathered mountain slopes are eroding from ancient sea-floor uplifted and broken by geologic stresses, frequently manifesting in the form of earthquakes.  The region is dry, though fog is common and periodic rainstorms can quickly drench the area, causing local flooding and landslides.  The dusty ground is colored a dull orange/tan with angular, flat, broken pebbles peeling out of shallow, soft bedrock with occasional anemonite and bivalve fossils.  Under the twelve foot chaparral canopy the gritty soil is overlain by several inches of slowly decomposing leaf-litter and twigs, loose in some places, held together by dense mycelial mats in other places, particularly under the scrub and live oaks.

Infrequent damp, cool places are home to massive coastal live oak (Quercus agrifolia) and California sycamore (Platanus racemosa) while a bewildering variety of woody shrubs make up the body of the chaparral cloaking the rest of the mountains.  Here and there small meadows, potreros in the southern California vernacular, and wind-blasted rock outcrops break up the gray/green vegetation.

Lemonade Berry (Rhus integrifolia) flower buds

Chamise, Toyon, Scrub Oak, Lemonade Berry, Ceanothus, Yucca, and various sages make up much of the more common large shrubs with Black Walnut, Elderberry, Coastal Live Oak, and California Sycamore making up the primary larger trees.  The softer vegetative plants of the understory tend be short-lived, only appearing to bloom and set seed after the rain.

The thick, leathery leaves of the Lemonade Berry (Rhus integrifolia) in the image above are fairly typical of chaparral plants in that they are mostly evergreen and have evolved to husband moisture.  Some plants steal their nutrients from other plants, Dodder (Cuscuta californica) is common in the chaparral, some years blanketing their hosts with yellow-orange leafless vines sporting nearly invisible flowers.

Dodder (Cuscuta californica) on Lemonade Berry. Dodder is most active after rains.

For such a dry region the diversity of both plant and animal life is astounding.  The most obvious animal life during the day are the birds.  Birds of all sizes everywhere, year round.  Little tiny acrobatic birds such as the Bushtit traveling in small noisy flocks.

Bushtit (Psaltriparus minimus) on scrub oak

Large birds of prey soaring overhead in search of thermals or their next meal.

Red-Tailed Hawk (Buteo jamaicensis) riding the wind

Meadowlarks, finches, wrens, thrashers, scrub jays, woodpeckers, hummingbirds quail, and a host of other birds flit about within earshot, if not within eyesight.

Western Meadowlark (Sturnella neglecta) atop a Toyon (Heteromeles arbutifolia) shrub, a popular food bush for many birds. Toyon is also known as Hollywood, the plant Hollywood owes its name to.

Anna’s Hummingbird (Calypte anna) perched on a non-native Tobacco Tree (Nicotiana glauca)

Mammals abound as well.  Small rabbits scatter like frogs in a pond in the evenings, and in the mornings I find fresh coyote, fox, bobcat, skunk, raccoon, deer, and mountain lion tracks on the unused dirt roads.  In the potreros badgers are not uncommon, large woodrat piles abound, bats fly through the canyons in the evening, and ground squirrels are everywhere.  Sometimes, if you have a quiet foot, a lot of patience, and good deal of luck you sneak up on these animals.  A few years back I was out here and found a coyote sleeping in the sunlight.

Coyote (canis latrans) sleeping in the sunlight

This being a dry area there are numerous lizards and snakes, mostly hidden from sight, and insects of all sorts.

I prefer wet places, places that stay green, but I do appreciate and enjoy the diversity of life here in the steep chaparral.  It is strange to be here between damp New England and my next home in Borneo where I will receive 3-4 meters of rain a year.

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Some of these photos are taken with a Nikon D80, some with a Nikon D90, and several with a Nikon D600.  I am still learning the latter camera, but if any of you out there are debating buying the D600, I can honestly say I recommend it.  The Meadowlark and Hummingbird images were taken with the D600 and are cropped from much larger images.

Birds, but especially Warblers

Birds occupy a place in our imagination like few other animals.  They are colorful, have beautiful songs, and they can fly!  Who doesn’t wish they could fly?

Young Red-tailed Hawk (Buteo jamaicensis) before the tail turns red

We eat them, decorate our bodies with their feathers, listen to their songs, and keep them as pets.  In westerns the high-pitched keening cry of the Red-tailed Hawk symbolizes the openness and loneliness of the range, setting the mood and implying that the rugged, lone gunman is as comfortable on the dusty range as the hawk is in the air.

Traditional societies have based dances on the mating dances of birds, clothing has been influenced by the color and patterns of birds, and we assign symbolism to specific birds; doves for peace, hawks for aggression, eagles for freedom, the unfortunate dodo as a dead-end in stupidity, and many more.

Here in the US the we chose the Bald Eagle to symbolize our nation, choosing a bird that is at least as much of a scavenger as it is a hunter, over the objections of Benjamin Franklin.  Make of that what you will.

Some birds live only a few years, others like parrots and albatrosses live as long as a healthy human.  Many birds can “fly” under water as well as in the air, the Water Ouzel of the American West, Loons, Cormorants, and Gannets that plunge into the water like falling rockets, diving many meters down to chase fish.  Some birds have given up the air entirely, Penguins retain their flight in the water, but the Ratities, an ancient lineage including Rheas in South America, Ostriches in Africa, Emus in Australia, and the extinct new Zealand Moa returned to their dinosaur origins, running at high speed on the ground, forgoing the air forever.

Corvids, crows and jays, Parrots, and Cockatoos are renowned for their intelligence, problem solving, and in the case of Corvids, tool use.  These birds rival small children and chimpanzees in their mental abilities.

Birds also can tell us about changes in climate and the environment.  Banding them allows for long-term identification of individuals.  Feathers can be analyzed for isotope ratios, telling what the birds have eaten and where.  Populations can be tracked to see how they respond to changes in environmental conditions.

Vermont Center for Ecosystem Studies employee banding a bird on Mt. Mansfield

I am not an ornithologist, I find birds to be largely mystifying.  I don’t seem to have the ear necessary to distinguish species based on their calls, a vital component of birding.  Despite this, I do greatly appreciate birds and try to photograph them when I can, in part to help me learn, in part because they are pretty, and in part because birds are often easier to see and are more prolific than many other animals.

Birding is a popular activity.  Of all groups involved in conservation and outdoor activities, birders have the highest average income, and companies that make the high quality spotting scopes and binoculars necessary for this activity adjust their prices accordingly.  Many of the most interesting and colorful birds are tiny and fast, necessitating patience and luck, or good equipment, or, most often, a combination of the two.

Warblers are popular birds to watch in New England.  New World Warblers are an often colorful group of small passerines, commonly called “perching birds”.  The name derives from their sparrow-like appearance.  Many of the New World Warblers over-winter in the neo-tropics, flying up to New England as the weather warms and food becomes available here.  Most of the ones I see are in the Septophaga genus, meaning “moth-eating”, though this is sometimes misreported as meaning “fly-eating”.  Others fall into the Cardellina and Geothlypis genera.  I am not sure what the origin of Cardellina is.  Several of the birds in this genus are reddish or pink, and others have a lovely song, it may be a comment on a loose similarity to Cardinals.  Geothlypis roughly means “earth warbler”, perhaps reflecting the essential silliness of many scientific names.

Over the last few years I have managed to take photos of a small number of them:

Canada Warbler (Cardellina canadensis)

This lovely little Canada Warbler was on the ridge-line of Shenandoah National Park and didn’t care that I was nearby.  I heard the song and had to hunt a little bit to find him.

Common Yellow Throat (Geothlypis trichas)

This Common Yellow Throat followed me through the woods as I waded through ferns and sedges in a wet wooded meadow near my house.  It didn’t seem afraid of me at all, more curious than anything.  It kept the caterpillars in its beak, suggesting that there was a nest with young close by.

Black-throated Green Warbler (Setophaga virens)

A few months back I heard a soft but rapid twittering in the woods on my morning walk.  Over my head a flock of 5 or so little birds flitted back and forth faster than I could follow.  One of them briefly touched down and held still for just long enough to snap this photo.  From there I was able to figure out that they were Black-throated Green Warblers.

Black-throated Blue Warbler (Setophaga caerulescens)

On our bird-banding day on Mt. Mansfield this little Black-throated Blue Warbler was found in the mist net.

Yellow-rumped Warbler (Setophaga coronata) western subspecies on the sunflower stalk, eastern subspecies held in hands

The Yellow-rumped Warblers may be the easiest of the warblers to see.  They range from California to New England and have been divided into several sub-species that are nearly indistinguishable to my eye.  The eastern variant is known as the Myrtle Warbler (Setophaga coronata coronata) and the western variant as Audubon’s Warbler (Setophaga coronata auduboni), but they are both Yellow-rumped Warblers to me.

Yellow Warbler (Setophaga petechia)

Finally this small Yellow Warbler was in an apple tree in deep shade.  It sat and watched me for several minutes, then flitted away.

Learning these birds has given me a greater appreciation for them, although I must admit that the task of learning these little guys would have been much more difficult if I couldn’t take photos of them and take the time to look closely at their details.

Photography as a tool

The foundation of science is observation.  Sometimes we need help making observations as the things we are interested in are small, far away, in motion, or complicated.  Not every observation can be made in the field or at real-time.

Fortunately, we live in a time where there are numerous tools to assist with observation.  One of my favorites is a camera. A good photograph can make the minute gigantic, the distant close, freeze time, and illuminate details otherwise unnoticeable.  Sometimes it takes some thinking creatively to capture and image, but the results can be worthwhile.

Nearly everyone is familiar with the incredible Hubble Space Telescope images of objects deep in space and far in our past (HST image gallery).  These images are extremely high resolution, taken using a wide variety of sophisticated techniques including multiple color bands, non-visible light, and dift-scanning, a way of tricking digital cameras into taking continuous images larger than their CCD receiving array.

Taken with an 1Phone 4 through a microscope eyepieceHubble style techniques are out of the range of most of us, but with a little creative thinking and a steady hand everyone can get some surprisingly good results with basic equipment.

In a soil ecology lab I was having trouble seeing some of the detail, and had to write a report on the nematode species I’d seen on the slide.  A photo was just the thing I needed, so I used the camera on my iPhone held over the compound microscope eyepiece to capture the image to the right (click image for a larger photo).

The same technique works well with a hand lens to capture shallow depth of field images of other small things, and with binoculars or a telescope to capture images at a distance.

I have a confession to make.  Despite being a naturalist and being reasonably knowledgeable about the natural world, when it comes to birds I am hopeless.  Those speedy little feathered dinosaurs flit hither and yon faster than I can see their detail.  They hide in shrubs or high atop trees and fly away when I come close.  Usually they are small and the identifying features are tiny, the diagnostic mark is often something like the color of an eye-ring or a barely seen flash of color on the nape of the neck.

The songs will tell you which bird is which, but not what they look like, and, in any event, I can never remember tunes.

I have turned to photography to recognize and identify birds.  I cannot get photos of many of them, miss shots of others, but I am slowly learning my birds.

Dark Eyed Junco

 Canada Warbler

 

Yellow-Rumped Warbler

Bushtit

 

 

 

To learn about the world we need to observe it, but it does not stop there.  We need to think about what we observe and question our observations.  Photographs offer a way of fixing our observations in time, allow us to revisit them, and invite reevaluation of them.