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)

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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)

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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)

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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)

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Dec 11 2012

Free Field Guide to Jewel Beetles

Have you ever seen a colorful, shiny beetle and wondered what it was?  I have.

There’s a group of beetles called Jewel Beetles that eat trees but are very beautiful.  Among them are the rainbow green Emerald Ash Borer and (perhaps) a solid green iridescent beetle I see in the spring whom I’ve dubbed The Emerald Green Bug because I don’t have a beetle guide.

But that problem is about to be solved.

In early 2013 the Canadian Food Inspection Agency, the University of Guelph Insect Collection and the Canadian Invasive Species Centre are going to publish a beautiful 411 page, 6×9″ Field Guide to the Jewel Beetles of Northeastern North America.

The guide covers 164 jewel beetles in eastern Canada and the northeastern U.S. including all of Pennsylvania.

One of the books authors, Morgan Jackson, describes the guide here on his blog and includes a cool slideshow of the emerald ash borer page.  I can tell the book is for bug lovers and entomologists yet it looks easy to use for generalists like me who are curious about the natural world.

And the book is FREE, absolutely FREE!

Click on the book cover or here to read Morgan Jackson’s blog and see if this is the book for you.  His blog tells you how to get your free copy.

I’ve already ordered mine.  Next spring I’ll know the real name of that “Emerald Green Bug.”

(cover of Field Guide to the Jewel Beetles of Northeastern North America, linked from Morgan Jackson’s biodiversityinfocus.com blog)

One response so far

Dec 10 2012

Duck Versus Goose

Published by under Quiz,Water and Shore

Dear Readers,

A question has been puzzling me for a long time and the answers I’ve found on the Internet are unsatisfactory, so I’m asking you.

What is the difference between a duck and a goose?

Is a duck smaller than a goose?  Not always.  The Muscovy duck is much larger than a Ross’s goose.

 

Does a goose have a longer neck or legs?  Not always.  Consider these black-bellied whistling ducks.

When we see a duck or a goose, intuitively we are able to say, “That’s a duck” or “That’s a goose.”

But how do we know the difference?

Please let me know by posting a comment.

 

(Credits:  mallard silhouette by Vlado on Freedigitalphotos.net, goose silhouette from ShutterstockMuscovy duck by B.Walker on Wikimedia Commons, Ross’s goose by Alan Vernon on Wikimedia Commons, Black-bellied whistling ducks by Sultry on Wikimedia Commons)

 

p.s. See the comments! The answer is there!

 

7 responses so far

Dec 09 2012

A Great Gift For Pennsylvania Birders

Published by under Books & Events

‘Tis the Season for giving!  If you have a Pennsylvania birder or scientist on your list, here’s a great gift idea.

The newly published Second Atlas of Breeding Birds in Pennsylvania by Andrew Wilson, Daniel Brauning and Robert Mulvihill is now available from Penn State University Press.  It’s a comprehensive, scientific look at all the birds who breed in Pennsylvania.

The data was compiled between 2004 and 2009 by over 2,000 volunteers.  I was one of them.  We traveled the state recording the location, habitat and behavior of birds during the breeding season.  Were they courting?  Building a nest?  Carrying food?  Were the adults scolding us for coming too close?  Did we see babies in the nest?  We took notes and uploaded our observations online.  Our data became this book.

It’s a beautiful book and fascinating for its discussion of breeding trends.  The second atlas (2004-2009) was done two decades after the first one (1983-1989) and a lot changed in Pennsylvania in those 20 years. Forests were cut down for highways and strip mines, old farms became suburbs and shopping malls, intact forests matured, former strip mines became grasslands, wetlands were lost or restored, and the climate continued to change.  The birds responded in their distribution and density.

The Second Atlas absorbs me every time I open it:  the trends, the species accounts, the maps.  I’m especially fond of the great success of Pennsylvania’s peregrine falcons (pages 160-161) who went from 3 breeding pairs in 1989 to 26 in 2009.

Click here or on the book cover to read more about the Second Atlas of Breeding Birds in Pennsylvania and buy it from Penn State University Press.  You can get a 20% discount online by using discount code SOC-12 during checkout.

(book cover photo from Pennsylvania State University Press)

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Dec 08 2012

Look At Me!

Here’s an Asian pheasant, a Temminck’s tragopan, that normally looks vermillion, black, white and brown.

When he’s in an amorous mood he shakes his head to begin his courtship display.  Two long blue horns pop up from his head and the small blue patch under his chin drops down to reveal an intricate iridescent blue lappet.

He opens his wings, puffs his body, and continues to shake his head to perfect his display.

And just in case his lady doesn’t notice, he clacks his beak.

Look at me!

Click here to see another Temminck’s tragopan with an even bigger, better lappet.  In a contest between the two, I bet the ladies will pick the guy with the bigger bib.

(video from YouTube)

 

p.s. The name “tragopan” has an interesting origin:  Trago is the Greek work for goat, Pan is the Greek god of the wild whose shape is half man, half goat.

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