Archive for December, 2012

Dec 21 2012

The Sun As Pearls

Published by under Weather & Sky

Like a three-strand necklace of pearls, this composite photo shows the sun’s position hour by hour at the summer solstice, the vernal equinox, and the winter solstice.

It was taken at the same location in Bursa, Turkey over a period of six months by award-winning amateur astronomer and night sky photographer Tunç Tezel, a member of The World At Night.

The top strand is the sun’s transit during the summer solstice in June, the longest day of the year.  You can tell the sun was up for 15 hours because there are fifteen pearls on that strand.

The middle strand was taken during the equinox when every place on earth has 12 hours of daylight.

The lowest strand was taken on this day, the winter solstice, when there are 9 hours of sunlight in northern Turkey.

There are nine hours of daylight in Pittsburgh today, too.

Northern Turkey and western Pennsylvania are on approximately the same latitude so these sun tracks are what we see here in Pittsburgh.

The whole world shares the same sky.  We all can see the sun as pearls.

 

(photo copyright by Tunç Tezel, member of The World At Night (TWAN).  This photo was NASA’s Astronomy Photo Of the Day on September 23, 2012.  Click on the photo to see the original and learn more about its creation.)

2 responses so far

Dec 20 2012

In Response To Daylight

Published by under Tenth Page

This week’s Tenth Page is on Thursday because Friday is an important day.

Tomorrow is the shortest day of the year, the winter solstice, when Pittsburgh will have only 9 hours 17 minutes of daylight compared to 15 h 4 m during the summer solstice.

This annual ebb and flow of daylight is an important cue for organisms that live in the temperate zone.

Birds, animals, plants, fungi and even blue-green algae all have internal clocks approximately 24 hours long.  Humans have long clocks: 24 hours and 11 minutes plus or minus 16 minutes.  Some birds have short clocks that run less than 24 hours.

The discrepancy doesn’t matter because our internal clocks reset every day in response to daylight.  In constant dim light we have no cues.  Experiments with common chaffinches show that their circadian clocks drift until their “days” are only 23 hours long in the absence of sunrise and sunset.

Birds also have circannual clocks that trigger their annual cycles of molt, migration and reproduction.  These clocks respond to the shorter days of fall and winter and the lengthening days of spring and summer.

After the breeding season birds’ reproductive organs shrink, an adaptation for flight that lightens their load during most of the year.  The shrinking is triggered by the decreasing light of fall and winter days.  After the winter solstice, the increasing photoperiod triggers their organs to grow in preparation for breeding.

Experiments with juncos show that they require a winter solstice for this to happen.  If the photoperiod increases without first decreasing, their reproductive organs don’t grow.

Our birds need the solstice to set their clocks.

(Inspiration for this Tenth Page is from page 250 of Ornithology by Frank B. Gill.    Photo from Wikimedia Commons; click on the image to see the original)

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Dec 19 2012

Named For…

Guess why this South American bird is called a Bearded Bellbird.

 

(video from YouTube)

p.s. that beard is not made of feathers.  It’s long stringy skin.  :-o

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Dec 18 2012

How Do You Say?

Published by under Plants

It’s poinsettia time so I went online to look for a pretty picture.  That’s when I got into trouble.

I searched Wikimedia Commons for poinsetta and found only four pictures.  Huh?  Only 4?  That cannot be possible.

One of the photos pointed to another view of the same plant and I finally got the hint.  I was spelling it the way I pronounce it.  I was spelling it wrong.

Poinsettias are native to Mexico where they are very leggy plants in the wild.  They were named for Joel Roberts Poinsett, first U.S. Minister to Mexico, who brought them to the U.S. in 1825.

The plant became popular as a Christmas decoration when Albert Ecke became fascinated by them, his son learned to make them into bushier, more beautiful plants, and his grandson promoted them on television in the 1960’s.  The rest is history.

Meanwhile, I was shocked — shocked! — to discover that there are two i’s in poinsettia and the second “i” should (or could) be pronounced.    I have never pronounced that second “i” and I wondered if this was a ‘Burgh thing (we have a notoriously vowel poor accent) so I conducted an informal poll.

How do you say the name of this plant?

So far, everyone I’ve asked says poin-SET-ah (no second “i”).  Two people knew about the extra “i” and one of them changed her pronunciation after she learned about it — but she didn’t start out that way.

I’ve heard that in some parts of the U.S. people say poin-SET-tee-ah, but if you’re from the Pittsburgh, well…    Poinsetta.

Hah!  No wonder I misspelled it.

(photo by André Karwath on Wikimedia Commons. Click on the image to see the original)

7 responses so far

Dec 17 2012

Singing Sand

Published by under Musings & News,Travel

I rarely spend time near sand dunes so I was amazed to learn that sand can sing.  In fact there are 35 places around the world where the dunes sing a low frequency hum in the bottom half of a cello’s range.

The droning happens naturally when the wind causes a sand avalanche.  People can force the song by pushing sand downhill.  The songs are well known but people have always wondered how and why they happen.

Some of the “how” is already known.

Singing dunes are crescent-shaped barchans with their backs to the wind and their horns pointing downwind.  The slipface is inside the crescent (downwind) with its surface at the angle of repose and a stationary layer beneath.

Experiments have shown the importance of the grains themselves.  If they’re spherical,  0.1 to 0.5 mm in diameter, and contain silica, they will sing in the lab when they slide down an incline.

This year physicists from Paris Diderot University discovered that grain size determines the tune.  They studied two dunes:  one in Morocco, one in Oman.   The Moroccan dune has grains 150-170 microns and emits a 105 hz sound (for musicians that’s near G-sharp two octaves below middle C).    The Omani dune has a variable grain size from 150 to 310 microns and its sound varies, too — from 90-150 hz (F-sharp to D).

Researchers took the Omani sand back to the lab and sifted it down to a nearly uniform size — 200 to 250 microns — and sent it down an incline.  Voilà.  The sand made a sound of 90 hz, close to the song of the Moroccan dune.  (Click here for more information about the study.)

What are the songs like?  In this video, filmed in Morocco, a man shows how he learned to make the sand sing.  Turn up your speakers and you’ll be able to hear a variety of sounds as he puts the sand through its paces.  The video is in French with subtitles, some of which are surprisingly translated as in the first sentence that says “Beware” when it means the less dangerous-sounding “Be aware.”

Thanks to science we’ve learned how the sand sings, but we still don’t know why.

(video from YouTube)

7 responses so far

Dec 16 2012

Awesome Thrush

Published by under Beyond Bounds

Though he looks like a fancy robin this is actually a varied thrush, a bird that breeds from Alaska to Northern California.

Most varied thrushes spend the winter south of their breeding grounds but a few individuals fly east and end up as far away as Maine and Newfoundland.

This one caused a sensation when he was found in Avon Lake, Ohio in early December.

Thanks to Shawn Collins for making the trip on December 9 and posting his photographs for all to enjoy.

(photo by Shawn Collins)

One response so far

Dec 15 2012

Speaking of Plumage

Published by under Bird Anatomy,Songbirds

Speaking of plumage as I did yesterday

Here’s a bird in juvenile plumage.

If you didn’t know that immature white-crowned sparrows are cream-and-brown colored, you’d have trouble identifying him.

Here’s what his parents look like in basic plumage.

Quite a difference!

 

(photos by Marcy Cunkelman)

5 responses so far

Dec 14 2012

Plumage Basics

Birds molt at least once a year to replace worn out feathers.  This process permits them to wear different plumages.

Some birds, like the American robin, look the same before and after.  Others radically change their appearance by replacing their fancy breeding feathers with plainer plumes.  Male scarlet tanagers are an extreme example:  They’re red while breeding and green while not.

Molt and plumage terminology was standardized in 1959 by Humphrey and Parkes who divided plumage names into three main types. (*)

  • Juvenile plumage is worn by young fledged birds.
  • Basic plumage is what birds acquire during their annual post-breeding molt.  We often call this “non-breeding” or “winter” plumage but these terms are inaccurate.  Adult robins are always in basic plumage even when they’re breeding, and “winter” describes the weather North America is experiencing while the bird is away.  To South American birders, a green scarlet tanager is in summer plumage.
  • Alternate plumage is optional.  Some birds don’t undergo a second molt but those who do put on their finest feathers in time for the breeding season.  This is often called breeding plumage.

In some species it takes several years for the young to mature so they progress through as many plumage cycles as it takes to become adults.  Young ring-billed gulls go through three cycles:  Basic 1, Alternate 1, Basic 2, Alternate 2, Basic 3, Alternate 3. Gulls are complicated.

American avocets aren’t quite so complex.  They molt their wing feathers once a year but change out their head and neck feathers twice a year from basic plumage (white) to alternate plumage (ochre) for the breeding season.

The avocets above are lined up in perfect sequence during their post-breeding molt in August.  The bird standing on the left is closest to basic plumage, the bird on the right is closest to alternate plumage, and the bird in the middle is halfway between.

 

Below, another flock has the lead bird closest to alternate plumage and the trailing bird closest to basic.

Look closely at each bird and you can see that the wings of the 1st, 3rd and 4th birds have ragged trailing edges because they’re molting their wing feathers.  The 2nd and last birds have perfect wings, so my guess is that they’re juveniles.  Juveniles don’t molt their fresh new wing feathers until they’re a year old.

When avocets have completed their molt into basic plumage their heads and necks are gray-white like this bird photographed in September.

 

Experts in molt and plumage can probably tell the age of these birds by their appearance.

Not I.  Aging shorebirds by plumage is my final frontier.

(Inspiration for this Tenth Page is from page 110 of Ornithology by Frank B. Gill.
All photos by Bobby Greene
)

 

(*) If you’re a plumage expert, please feel free to correct me.  I’m still learning!

P.S. TO PEREGRINE FANS:  Molting is a wonderful thing.  Last May the male peregrine at Pitt, E2, chased off an intruder but not before this opponent damaged one of his primary feathers.  This gave him a “hole” in his wing.  Over the summer he completed his annual pre-basic molt and grew all new feathers.  Now his wings are perfect.  No gap.

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Dec 13 2012

Birds On Ice: Dovekie

Yesterday I wrote about copepods and polynyas so I could introduce this bird, the dovekie.

Though I visit Maine every September and even take pelagic trips in the Gulf of Maine, I have never seen a dovekie.  That’s because they breed on islands in the High Arctic (Baffin Island, Greenland, Iceland, etc) and don’t leave their breeding grounds until late August.  At that point they’re molting and flightless so they drift on the southbound current to spend the winter in the North Atlantic.  They usually aren’t seen off the coast of Maine until November.

Dovekies (Alle alle), also called little auks, are cute little seabirds the size of starlings but much fatter — two to three times the weight of a starling.  They are so numerous that there are tens of millions of them in the North Atlantic in winter.

The two shown above are in breeding plumage at Svalbard.  Their eyes are black but look white in this photo because they’re half closed.  Perhaps they’re whispering sweet nothings to each other.

In the U.S. we only see dovekies in winter plumage.  Here’s a video of one off the coast of North Carolina in January that gives you a sense of how tiny these birds are.

 

In the breeding season dovekies depend on cold water and ice.  Copepods are their favorite food — sometimes their only food — so they locate their breeding colonies near polynyas where copepods are plentiful.   In a curious way they’re an edge species, preferring the fertile edge where ice meets open water.

Dovekies are so numerous that you’d think that nothing could threaten their survival.  Unfortunately they are easy to hunt at their breeding colonies and global climate change may lower their breeding success.

But who knows?  Maybe The Big Melt will help dovekies for a while.

 

(photo by Michael Haferkamp on Wikimedia Commons. Click on the image to see the original)

6 responses so far

Dec 12 2012

What The Heck Is A Copepod?

There’s a bird I want to tell you about but his lifestyle involves words so unusual that we have to learn a new vocabulary before I can introduce him.

The bird eats copepods and is fond of polynyas.

What the heck is a copepod?

The word “copepod” actually describes the animal it names.  “Cope” is from the Greek word for “oar” and “pod” is Greek for foot.  So a copepod is literally an Oar-Foot.

Copepods are tiny, usually transparent, crustaceans with oar-like antennae. They live in wet places:  oceans, lakes, rivers, streams, swamps, bogs, and even in the water in caves.  They are very small, often microscopic, and very numerous.  There are 13,000 known species.  The vast majority live in the ocean.

And, yes, they are small, typically only 1-2 millimeters long (0.04 to 0.08 inches).  Living at the bottom of the animal food chain, they ultimately support creatures as big as whales and are the primary food source of the bird who spawned this thread.

In the Arctic, copepods are especially plentiful in polynyas, which is why the bird is fond of polynyas.

A polynya is a big hole of open water surrounded by ice.  The word comes from the Russian word for hollow.  (Click here to see two polynyas in Antarctica and a photo of their green, algae-laden water.)

Some polynyas are permanent, others are seasonal.  Off the coast of Canada, the North Water Polynya opens every spring between Ellesmere Island and Greenland.  When it does, new sunlight entering the water causes a microalgae bloom, the copepods swarm to eat it, and our mystery bird arrives to eat the copepods.

But more about him later.

(copepod photo by Ume Kils on Wikimedia Commons.  Click on the image to see the original)

One response so far

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