Sunday, November 28, 2010

White-throated Sparrows

The white-throated sparrow, Zonotrichia albicollis.

White-throated sparrows are back and they love black oil sunflower seeds! Three of them have been coming to my Brooklyn porch for breakfast all week.

Most white-throated sparrows spend the summer breeding season in Canada. Then they migrate south to spend the winter in the eastern and southern states, on the west coast, and in northern South America.

I usually hear white-throated sparrows rustling in the leaves before I see them. They forage for insects and seeds in brush piles and under bushes. They flick their heads to toss leaves aside. They use both feet to scratch backward and then jump on anything they scare up. They spend a lot of time on the ground, hopping instead of walking.

Their habitat is usually described as woods and forest edges, but they like parks too and they are at home in extreme urban landscapes like New York City where they forage side by side with house sparrows. The white-throated sparrow is brown above and grey below, like a house sparrow, but it is distinguished by a striped head, a yellow spot between the eye and the bill, and, of course, a white throat.

White-throated sparrows come in two genetically determined color varieties. One has bold white markings and the other has muted tan stripes. The color forms are maintained by a complicated set of mating preferences. Males prefer white striped females but females prefer tan striped males. White striped birds are more aggressive, so white striped females may have a competitive edge in pairing with  sexy tan striped males. The gene pool refills with both kinds.

Sunday, November 21, 2010

Spider Business

Remember the spider I wrote about last week? The one that makes cobwebs on my ceiling? She had an eventful week!

First, she shed her skin! She molted! On Monday morning, there seemed to be two spiders where there had been one. Closer inspection revealed this:

Female triangulate spider, Steatoda triangulosa, with her newly shed skin. 

That's her old skin on the right. It's stuck in her invisible web on the ceiling next to the light outside my bathroom. Notice how the spider's new legs are almost transparent? After spiders and insects and other things with external skeletons shed, they are softer, lighter colored, and more flexible than usual -- like soft-shelled crabs. They are actually incapacitated while they wait for the new skin to harden. Our girl sat still next to her old skin from Monday through Thursday, while her new skin dried, hardened and darkened. The new skin has tiny folds that expand to accommodate her new bigger size. Apparently my home provides enough insect prey to support a growing spider. Come to think of it, I haven't seen any other insects in here lately.

Then, she got a boyfriend! On Tuesday morning there really were two spiders where there had been one! He is on the left in the photo below.

All I saw of their relationship was the two of them sitting motionless side by side, but chances are good that there are spiderlings in our future. To mate, a male spider spins a "sperm web," and deposits sperm in it using sex organs on his rear abdomen near his silk spinning organs. Then he takes sperm from the web with a pair of organs near his mouth, called pedipalps. When he gets the chance, he inserts his pedipalps into paired sperm receptacles under the female's abdomen. Both genders have pedipalps, which look like very short legs -- females use theirs for touching things and handling food. Mature male pedipalps have enlarged ends that look like tiny boxing gloves.

By Friday morning the female's new skin had hardened. She had a spurt of activity and ran around for a few feet in all directions in her new outfit. She returned to the center, near her old skin, and approached the male. They faced each other with their front legs spread wide. When they both suddenly and unexpectedly fell from the ceiling, I squeaked and ran away. We all recovered quickly. They climbed up threads. I went back to watching them. They went back to sitting motionless.

On Saturday morning the male was gone.

Things are back to normal. But the female is bigger and possibly inseminated. If she has eggs she will spin a protective case of silk and hang it in her web. We'll know before long!

Sunday, November 14, 2010


The triangulate household spider, Steatoda triangulosa.

The triangulate household spider above is a female. Like all spiders she has eight legs and two body segments. Her large round abdomen is decorated with brown triangular spots. She is about 1/4 of an inch long, with bands of darker color at each of her leg joints.

She has just settled into a spot close to the ceiling light outside of my bathroom. She has been there for three days, moving only slightly to change position. Day and night, she hangs upside down from her almost invisible web.

The spider below is a male of the same species. He lives in the vicinity of a framed photograph that hangs in my hall. Triangulate spiders are among the most common harmless household spiders of North America. They were introduced from Eurasia.

Triangulate spiders (and other cobweb spinners in the scientific family Theridiidae) make webs from short stands of sticky spider silk arranged irregularly. Their webs are not the pretty symmetrical kind that garden spiders make, but they work just fine.

Triangulate spiders hang upside down waiting for insect prey -- ants, fleas, ticks, and other tasty things. They rush over to wrap up ensnared prey in more silk, and eventually kill and eat them.

The cobwebs that triangulate spider spin probably got their name from an Old English word for spider, attorcoppe, which was eventually shortened to coppe and led to coppeweb or cobweb. Fans of J.R.R. Tolkien will remember when Bilbo the Hobbit tried to enrage the giant spiders of Mirkwood by jeering at them: "Attercop! Attercop! are fat and lazy, you cannot trap me, though you try, in your cobwebs crazy!"

Abandoned cobwebs gather dust and gradually become more visible. I don't knock them down unless they are empty, not wanting to interfere with the capture and consumption of insect pests. No good housekeeping seal of approval for me -- I harbor cobweb spinners!

Sunday, November 7, 2010

The Bird King

Troglodytes troglodytes, the winter wren.

I saw this little wren in Cadman Plaza Park in Brooklyn, New York. He was on the ground, hopping in and out of sight under a row of shrubs. He perched momentarily on a low branch and then dove into the underbrush.

Don't feel bad if you have never seen a winter wren. Even though they are common, they are tiny. They weigh less than half an ounce and are only about four inches long. We often only notice them as they scurry away under bushes. It is easy to mistake them for mice.

The winter wren usually holds its short tail cocked upward. The bird is warm brown with dark narrow bars on wings, tail, and back. It has a light stripe above the eye. Its chin and throat are grayish brown. Its short round wings allow it to take off quickly and to maneuver around in the close environment of brush and bush.

In North America, winter wrens breed in northern Canada and then move south into most of the United States to spend the winter. They live in habitats from remote islands to crowded cities, but they prefer conifer forests. The winter wren is the only wren that is also found outside of North America, in Europe, Asia, and Africa.

Although winter wrens eat insects, they are able to find enough food in cold weather by foraging on bark and fallen logs. They are usually not social during the day, but may spend nights huddling in groups in snug cavities; it is warmer that way.

The winter wren is famous for singing. Only the males sing, but unlike many birds that sing only during breeding season, winter wren males sing year round. The little wren puffs his chest, cocks his tail, tilts his head back, and sings a long stream of musical trills. Follow this link to watch a wren singing on YouTube:

Now about the title. According to folklore via Aesop's Fables and Grimm's Fairytales, the winter wren is the very unlikely King of the Birds. Apparently it was decided long ago one day when the birds were talking about who should be king. They agreed to decide by a flying contest and they all took off skyward. Over time they dropped back one by one, first the little birds, then the heavy birds, until eventually only the eagle was left.

But no! A little winter wren (called simply the wren in Europe where it is the only one) was hidden in the eagle's feathers. The wren won on a technicality -- being on the eagle's back and therefore higher, or in another version, by jumping off and flying upward after the eagle finally got tired. The wren reached heaven and proclaimed his victory with song. (The moral is that cleverness is superior to strength.)

The birds were upset and demanded a redo. They decided to see who could go deepest underground. They all started digging and tired themselves since most were not really made for the work. The winter wren popped into a mouse hole and won again. He sang his victory song again. The birds were really mad, but tired. They posted an owl to watch the mouse hole and went away to rest. The owl fell asleep. The wren got away, but to this day feels uneasy and stays hidden in the bushes. The owl, humiliated by failure, no longer goes out in the daylight and gets revenge by eating mice...

In England, the Queen of the Fairies was thought to shapeshift into a wren called Jenny. Lots of nursery rhymes feature wrens. Here is a sampling.

This one, which captures the wren's typical resting habit, is best read aloud: 
          Little Jenny Wren
                                                       A little Jenny wren, 
                                                       was sitting by the shed.
                                                       She wagged her tail,
                                                       and nodded with her head.
                                                       She wagged her tail,
                                                       and nodded with her head. 
                                                       As little Jenny wren,
                                                       was sitting by the shed. 

This one refers to the winter wren's fecundity. A pair of winter wrens can raise two 1-9 egg  clutches in a year. 

The Dove and the Wren

The Dove says coo, coo, what shall I do?
I can scarce maintain two.
Pooh, pooh! Says the Wren, I've got ten,
And keep them all like gentlemen. 

And here is one that refers to the winter wren's drab plumage. 

When Jenny Wren Was Young

'Twas once upon a time, when Jenny Wren was young, 
So daintily she dance and so prettily she sung,
Robin Redbreast lost his heart, for he was a gallant bird, 
So he doffed his hat to Jenny Wren, requesting to be heard. 

"Oh, dearest Jenny Wren, if you will but be mine, 
You shall feed on cherry pie and drink new currant wine, 
I'll dress you like a goldfinch or any peacock gay, 
So, dearest Jen, if you'll be mine, let us appoint the day."

Jenny blushed behind her fan and thus declared her mind: 
"Since dearest Bob I love you well, I'll take your offer kind. 
Cherry pie is very nice and so is currant wine, 
But I must wear my plain brown gown
And never go too fine."