Which way is down??

Sometimes I find myself wondering about a phenomenon so ordinary that I had taken it for granted all my life. Mushrooms always orient themselves so that the cap is horizontal, with the spore-producing surface pointing down.

Chicken mushroom

Up to this point, I’m OK. I know that they disperse their spores by simply opening up the gills or tubes to let the spores fall down, and then the wind will catch them. And the upper surface acts to keep the spores dry, essential to their proper dispersal. But here is the question: how does the mushroom know which way is down.

Perhaps it works like in plants. The stalk goes straight up, towards the sun, and the cap just ends up horizontal, at right-angles to the stalk?? But plants have a reason to reach for the sun, they need it to photosynthesize. If they grow in the shade, they may lean sideways towards the sun, and sunflowers turn their entire flower not upwards, but at an angle to face the sun. This one had fallen over in a storm, and contorted itself around back to the sun’s rays.

Mushrooms don’t do this. The cap just faces up and the gills down. And they can grow in very dark places (although some do in fact need light and react to it.)

The urge for the cap to face down is very strong. If the stalk emerges sideways to avoid a rock or a root, it will bend upwards as soon as it can, so that the cap faces down.

Sometimes the mushroom emerges straight, and then gets knocked over by a passing creature, like a beagle (!).

But the following day it has begun to compensate:

Leccinum sp.

and in one more day it is splendidly resurgent:

This by the way is an 8 inch chunky bolete; there is an acorn at the base of the baby one, for scale.

Bracket fungi, with no stalks, grow straight out of the tree at right-angles, like these polypores on the right edge of the still-standing remnant of the trunk below:

And when the tree falls, the new growth simply rotates itself through 90 degrees so it is facing down again. It’s a little hard to explain in photos, so I’ve given you three attempts below. In each image the old fungi that grew before the fall are vertical now, seen thin edge-0n, and the new ones are horizontal.

So how DO they do it?? Remarkably, it appears that they sense gravity. Just like us. Our ears contain tiny calcium beads called otoliths (‘ear stones’), which float around and brush against tiny hairs and thus remind us of which way is up. If they get loose, our sense of gravity goes wrong and we feel dizzy. It seems that fungal cells may have a similar way of sensing gravity, so they always know which way is down. The nuclei in each cell act a little like otoliths, and the whole fungus responds.

The phenomenon is called gravitropism*, and here are two more successful examples.

If you’d like to know more, here is an excellent article.

*The shelf mushrooms that restart new versions at right angles to the previous ones are technically examples not of gravitropism, but of gravimorphogenesis, since the original doesn’t reorient itself, only the new growth is sensitive to gravity.

PS Rather wonderfully, fungi have been taken into zero gravity in space to see how this affects them. Many of them not surprisingly get too confused to form proper fruiting bodies at all!

A brown pin-striped heron? Really?

Last week I was kayaking on my marshy beaver pond, and I found a young heron standing in the scrubby shallows, watching me.

He wasn’t easy to see. In the spirit of “Where’s Waldo?” , can you find him?

He is dead center, just to the right of the bushy green trees in the center of the picture. My kayak is bottom right.

His stripy brownish plumage and all-black cap mark him as a juvenile Great Blue Heron, Ardea herodias:

His wing and breast have quite distinct patterns, elegant beyond belief.

He seemed not bothered by my presence, so I gradually got quite close. Something caught his eye, and he curved his neck into the classic S-shaped pose readying himself for a strike:

It was probably a frog, a favorite food of juveniles who are not yet very good at catching fish, but it all came to naught, and I left him in peace amongst the golden leaves and red winterberries:

PS: When he is all grown up, his plumage will be quite different. The dowdy brown will fade, and those white streaks are the start of what will one day be a dramatic cascade of white plumes on his chest. Here is the same young bird the next day in a different pose, so you can see the stiff white quills (taken from the far side of the pond, so it’s a bit blurry):

And here is his future self, long neck-plumes and all:

plus a drifting fan of them across his back.

(This one was stalking around the lake in July.)

PPS: Kushlan says: “Herons usually catch prey with a Bill Stab, which is a downward or lateral strike involving fast, directed movement of the head and neck while the body remains still. This is the characteristic capture stroke of the long necked herons, which have full development of specialized neck vertebrae, the elongated sixth cervical vertebra acting as a hinge for the forward strike.”

Kushlan, J. A. 2011. The terminology of courtship, nesting, feeding and maintenance in herons. [online] http://www.HeronConservation.org

Underground Stars

One of the oddest, least plausible creatures in my Maine world is the Star-nosed Mole. Being moles, they live almost entirely underground, and the only ones I have ever seen are dead. These photos were taken this morning, after my dog spent a long time sniffing very tentatively at something unfamiliar. The mole looked peaceful, and as if it had not been dead for long, with no signs of injury.

Condylura cristata is native to the Northeastern US. It is a small grey creature, about 8 inches long, 1/3 of which is tail. Its head is at the bottom center below:

It has outsized feet with five imposing claws for digging:

But the really remarkable thing is its nose. It ends in 22 fleshy finger-like tentacles:

These are covered in sensory receptors that respond to touch and perhaps vibrations. They can each move independently and flex by 90 degrees, and they are sometimes all grouped together pointing forward, and sometimes opened up like petals. Here is a close-up, showing the 11 tentacles surrounding each nostril:

They are covered in 30,000 tactile receptors called Elmer’s organs, that contain more than 5 times the number of nerves in a human’s hands. The mole “sees” the world through these tactile receptors. The tentacles aren’t used for grasping anything, or for digging, just for feeling their world. Someone described it as the “nose that looks like a hand but acts like an eye.” (Their actual eyes are tiny, just visible in the third photo of this post.)

They tunnel underground, deep down in winter but close to the surface in summer, where the earthworms are. The tunnel pushes up the ground, as you can see in this photo, where the tunnel goes from top to bottom of the picture, across a human trail.

They sometimes break through the surface, as they did in the small round hole bottom right here:

When I was reading up for this post, I discovered to my astonishment that they are very strong swimmers. “My” mole was close to a marshy area and a stream, and apparently this is typical. Although they live on land, many of their burrows end at the water’s edge, and they eat not only earthworms but also aquatic imvetrbertaes. I would give a lot to see one swimming. They use that nose in the water to to sense their surroundings. This wonderful short video shows them foraging both underground and in the water.

It turns out other species may use the same technique, as this fluid dynamics expert explains:

They remind me of a duck-billed platypus, another implausible aquatic fur ball with a cartoon face.

PS Kenneth Catania is a leading expert on star-nosed moles, and he has written a wonderful book about both them and other unlikely creatures, called Great Adaptations. https://press.princeton.edu/books/hardcover/9780691195254/great-adaptations

The Little Wren*

The House Wren, Troglodytes aegon, weighs only 11 grams, or 0.35 ounces. And it is brown, so for someone like me (novice birder, terrible eyesight) they are easy to miss. I have a new app, the Merlin Bird Pro Sound ID, which is the first I have ever used that seems to really work, and the other day it told me I was listening to a House Wren. And then today, I saw one, or maybe two.

First, I saw one on top of a trellised arch in my garden, smaller than the morning glory flower behind it:

It had been raining, and it was preening:

And I think it was a juvenile, judging by the fluffy plumage.

It flew off, and a few minutes later either it or its doppelgänger emerged from the undergrowth with a huge grub:

I have no idea if it was the same one, or just possibly its mother, valiantly still feeding the recently fledged youngster. We are at the Northern edge of their breeding range, and soon they will migrate to the Southern US and Mexico for the winter.

I failed to get a recording of the House Wren song, so I’ve put in this Winter Wren, Troglodytes hiemalis, song instead, also in my garden about a week ago.

PS The North American House Wren is a different species from the wren we have in the UK, whose scientific name is Troglodytes troglodytes. Troglodytes comes from the Greek, meaning “one who creeps into holes”. House Wrens nest in cavities in trees or sometime rocks, so I think that’s the source of its scientific name.

*William Wordsworth knew this well. Here are the first few verses of his poem, A Wren’s Nest, written in 1833 (obviously about an English wren). I have bolded the key phrase that displays his knowledge of their preference for nesting in cavities.

AMONG the dwellings framed by birds 
In field or forest with nice care, 
Is none that with the little Wren’s 
In snugness may compare. 

No door the tenement requires, 
And seldom needs a laboured roof; 
Yet is it to the fiercest sun 
Impervious, and storm-proof. 

So warm, so beautiful withal, 
In perfect fitness for its aim, 
That to the Kind by special grace 
Their instinct surely came. 

And when for their abodes they seek 
An opportune recess, 
The hermit has no finer eye 
For shadowy quietness. 

These find, ‘mid ivied abbey-walls, 
A canopy in some still nook; 
Others are pent-housed by a brae 
That overhangs a brook. …

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