Month: February 2019

[I’m off to Ethiopia tomorrow, so expect no posts for a couple of weeks, and then a change of subject matter on my return!]

A surprising number of animals find a use for tree bark.

In my last post two grey squirrels were getting together in the treetops, but my sharp-eyed husband noticed that they had already prepared for the consequences of their dalliance: higher in the same tree was their drey:

The base is made of leaves, but look at the top: a mound of shredded bark.

And indeed if you now take a second look at their marital embrace, you can see that earlier one of them had been hard at work harvesting bark:

Foresters hate grey squirrels as much for the damage they do to trees as for any effects on our native red squirrel population.

Beavers of course operate on an altogether larger scale.

This quite sizable tree was felled behind my house in Maine a few years back, and within a few days they had systematically stripped off huge areas of delicious bark.  What they like is the living cambium underneath the bark itself. It is the innermost phloem layer that carries nutrients from the photosynthesizing leaves to the rest of the tree, so it contains delicious sugars and minerals.

Sometimes it may also help them get a grip when they are maneuvering a log into position for a dam or lodge:

and often they just gnaw the bark off a standing tree, sometimes killing it.

Porcupines love tree bark.

My friend Leigh posted impressive evidence of porcupine work in her blog recently:  scroll down about half way for the porcupine aftermath photos:

Poking About Among the Trees

Many other animals, including deer, rabbits, voles and mice eat bark too. Apparently so can humans:

https://www.offthegridnews.com/extreme-survival/edible-tree-bark-the-ultimate-survival-food/

Bark also has its own mysterious beauty:

Bark World, by Olivia Bayard (from The New Statesman, July 2016)

Rough, tough to touch,
grooved ridged scaled –
textures and fissures
teeming with the fuss and
stress of being –
dark crevices
crammed with mini-beasts
– woodlice, beetles, borers –
and wispy spiders, that scurry
across burled highways –
algae
lichen moss growing warmth, cover
over tiny birds tight in dark holes,
feather to feather, beak to beak
– a claw here, an eye there –
flutter shuffle, first squawks
and squeaks –
and the deep inside,
where sap rises rich and quick,
grains, circles, lines,
the yearly marks of tell-time –
old time,
now time, pest, blight, disease time,
warming time, losing time,
a stopped clock at felled time.

Happy Valentine’s Day!

I live near Brompton Cemetery, a grand Victorian green oasis near Chelsea FC.

The story behind this extraordinary gravestone is one of the more remarkable ones: https://en.wikipedia.org/wiki/Reginald_Warneford

But this week, the sun was shining, and everyone decided it was spring. The trees:

The birds:

You can hear this European Robin, Erithacus rubecula, song here:

And the squirrels, doing their Cirque du Soleil trapeze act imitations:

After playing hard to get in a “mating chase”:

She selected one from a trio of suitors, and there they enjoyed a precarious tryst high, high in the treetops. The tail says it all:

She will have a litter of 3-4, after a gestation of 44 days. Females can breed at 10-12 months, and often have two litters per year. They may live to the age of 5, so at up to 8 young per year for four years, that is 32 young per female. There are about 2.5 million grey squirrels in the UK, and you can see why their introduction from the US has overwhelmed the more sedate British reds.

Their Chinese name is sōngshû, or ‘pine tree mouse’, 松鼠. The second character looks very mouselike!

PS My computer refuses to put the right accent on the ‘u’ in sōngshû. Sorry to those of you who know it should be a ‘v’ shape, not a little hat. 

 

 

Most mammals (including the great apes) and many species of birds have dark brown eyes.

We forget that humans are unusual in having a wide variety of eye colors: brown, blue, grey or hazel/green.

And in fact elsewhere in the animal kingdom, we find the same eye colors recurring. This Ugandan Grey-necked Crowned Crane, Balearica regulorum, has pale grayish-blue eyes.

This Common Cormorant in Central London has eyes greener than those of any human outside Scifi movies:

And this dragonfly goes one step further:

But we also find eye colors that in humans would need contact lenses:

Look at this White-eyed Buzzard in India:

Or the lemon yellow eyes of the Indian Jungle Owlet:

or the tawny eyes of the lion:

and the tangerine eyes: of the Namibian Southern White-faced Scops Owl, Ptilopsis granti

Maddest of all, the cherry-red eyes of the loon (aka Great Northern Diver):

The dragonfly aside, the mechanism for all these eye colors lies in the outer layer of the iris, called the stroma. Dark brown eyes result from the presence of melanin in the stroma.  Blue eyes happen when the stroma contains no pigment and is translucent. This layer scatters the white light, and it scatters the shorter blue wavelengths the most, giving rise to the perception of blue eyes. If the layer has a little more collagen, the blueness is dampened and the eyes look grayish. Green eyes result from the presence of a little melanin only, mixing with the reflected blue to create green.

There are actually two types of melanin, and the full range of colors found in my photos above depends mainly on which type of melanin is found. Here is a great chart, if you’d like to know more.

Melanin Content and Eye Color

Eye color	Melanin Presence on Front Layer of Iris	Melanin Presence on Back Layer of Iris	Dominant Pigment Type
Brown	Heavy	Normal	Eumelanin
Blue	Light	Normal	Eumelanin
Gray	Even less than blue	Normal	Eumelanin
Green	More than blue eyes, less than brown	Normal	Pheomelanin
Hazel	More than green, less than brown	Normal	Pheomelanin and Eumelanin
Amber	Heavy	Normal	Pheomelanin
Red or Violet (in humans)	None or extremely little	None or extremely little	n/a

 

PS Humans are also unusual in having the colored iris surrounded by a large white area, the sclera. This makes it easy to notice the direction of other people’s gaze, a useful trait when cooperating with others.

Many animals and birds have striking markings around their eyes, made of fur, feathers or just plain skin. Why?

Pale circles round the eye may help gather extra light for animals that feed in reduced light. Dark circles around the eyes may reduce glare for animals that feed in bright light. Often, though, these markings have no precise function. They either disguise the eye, or break up and confuse the head contours, or aid in species recognition. Here are some examples.

The American red squirrel has elegant white semi-circles above and below its eye, probably helpful in noticing predators when feeding in dappled light:

Raccoons famously sport dark highwayman’s masks, but it seems unlikely that reducing glare is their main function, since raccoons are largely nocturnal:

Wood frogs too have dark masks, and they live mainly in thick woodland, where the light is not bright. (Though the dark lines in front of the eye may help in accurately targeting prey.)

But the Southern Masked Weaver’s dark mask may indeed be an adaptation to reducing the glare of the Namibian desert:

And the Egyptian Goose, although this one now lives in Hyde Park in London, originates from Africa and so its dark eye circles may not just be the result of a late night out, but may have given it an edge in that bright light:

My last few examples are almost certainly not aids to vision of any kind. Just like our eye makeup, they may serve to attract a mate. Whatever works for you…

In Maine, the wood doves have pale blue eye-liner: a look I am considering for next summer.

In Ecuador, both the male Masked Trogon  (first photo) and the female (second photo) wear red-rimmed spectacles:

As does the Zambian Three-banded Plover:

Here in the UK, the common blackbird has sharp yellow circles:

But these are outdone by the Ecuadorian the Cock-of-the-Rock’s astonishing yellow goggles:

Finally, by popular demand, the Plate-Billed Toucan: not exactly an eye ‘ring’, but the most flamboyant choice of eye shadow shades that I know:

Humans need more help:

[James Charles is sponsored by Covergirl. He is the beauty blogger phenomenon who stopped traffic in Birmingham last week. ].

If you’d like to know more about natural eye makeup, read this:

Ficken, Robert W., Paul E. Matthiae, and Robert Horwich. “Eye marks in vertebrates: aids to vision.” Science 173.4000 (1971): 936-939.

PS There is a separate story about the color of the eyes themselves. Maybe I’ll look at that next.