Archive for September, 2008

Sep 29 2008

Ornery

Sharp-shinned hawk (photo by Marcy Cunkelman)Now that the broad-winged hawks are south of us, the most numerous species at Pennsylvania hawk watches are sharp-shinned hawks

Rainy weather kept eastern migration numbers low for the past few days but the mix of raptors has changed nonetheless.  At Hawk Ridge in Duluth, Minnesota, where the weather’s been better, there was an enormous peak of broad-winged (BW) numbers on September 15th.  After that, sharp-shinned (SS) numbers grew. 

As hawk watchers will tell you, “sharpie” migration does not make for friendly skies.  Sharp-shinned hawks are ornery – even belligerent – on the wing.  Though they prefer to migrate in small groups, they frequently pick fights with fellow travellers.   A typical sharp-shinned fly-by goes like this:  

A sharp-shinned hawk approaches, flying its characteristic flap-flap-glide pattern.  One or two other sharpies are with him and maybe a kestrel.  The birds in this little group make good progress until one of the sharpies decides he can’t stand the guy next to him and dive-bombs him.  The bird he attacks takes evasive action or attacks in turn.  They spar for a while - as they migrate! - then calm down and resume normal flight.  This happens over and over.

It’s a wonder that sharpies waste time fighting on migration.  They’re so lightweight that they have to flap more than other raptors to make headway and course corrections.  You’d think they’d save their energy for flying.

But sharp-shinned hawks are highly territorial – so much so that the female attacks her mate if he waits near the nest after delivering food. 

Sharpies even go out of their way to attack raptors that could eat them.  Perhaps they think that the best defense is a good offense, but it doesn’t always work.  Many a sharp-shinned hawk has ended up as lunch after attacking a peregrine falcon.

(Photo by Marcy Cunkelman, taken through her scope.)

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Sep 26 2008

Oh my gos(h)!

Published by under Birds of Prey

Immature Northern Goshawk (photo by Debbie Waters, Hawk Ridge Bird Observatory)Two weeks ago in Maine a red squirrel and I both had a close call.  He escaped with his life and I got a thrill. 

I was sitting outside the Harbourside Inn at dawn drinking my morning coffee when I heard a rustling sound and a red squirrel’s frightened scream. 

Fifty feet away a hawk was chasing breakfast, hopping fast through the trees with wings outspread.  His prey, the red squirrel, was cheating death.

Brown and white with a bold white eyebrow and long, powerful, yellow legs the bird had the wingspan of a red-tailed hawk.  “Oh my gosh!” I thought, “it’s an immature northern goshawk!”

Until that moment I had never seen a “gos” (*) on the ground.  I’d only seen them during quick fly-bys at hawk watches and often needed help identifying them.  Not so with this bird.  This one fairly shouted “I’m a gos!”

Northern goshawks are the largest North American accipiter.  Truly a northern bird, they don’t leave their territory in winter unless their food supply crashes.  In Pennsylvania they nest in the northern tier and only come to the southwestern part of the state in winter, but because they prefer forested areas to cities and suburbs it’s unusual to see them in Pittsburgh. 

Goshawks are well known for fiercely defending their nests, aggressively attacking humans and even killing raptors who nest nearby.  If this bird had been an adult during nesting season I would have been in serious trouble sitting only 50 feet away.

Fortunately the goshawk was young and intent on his meal.  I watched the red squirrel escape and the goshawk fly to a perch deeper in the woods. 

What a privilege to see him!  Though it was a stressful morning for the squirrel, I’m glad he was there to tempt the hawk into the open.

(Thank you to Debbie Waters, Hawk Ridge Bird Observatory, Duluth, Minnesota for her photo of an immature northern goshawk)

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(*) A note on pronunciation:  “Gos” (pronounced “goss”) is the birders’ nickname for the species.  “Goshawk” is pronounced “goss-hawk.”

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Sep 24 2008

Eloquent Eggs

Published by under Books & Events

Guira Cuckoo (Guira guira), eggs 2006 © Rosamond Purcell If you’re interested in birds – or photography – you’ll enjoy the exhibit opening tomorrow at Silver Eye Center for Photography entitled Eloquent Eggs and Disintegrating Dice: Photographs by Rosamond Purcell

For over 25 years Rosamond Purcell has photographed behind the scenes in major museums, producing stunning photos of rarely seen collections.   This exhibit features eggs, nests and birds from The Western Foundation of Vertebrate Zoology in Camarillo, California, the largest collection of eggs and nests in the world.  Also on display will be six photos of celluloid dice from magician and actor Ricky Jay’s collection. 

Shown here is Ms. Purcell’s photo of Guira Cuckoo eggs, just a hint of the beauty to come in her book Egg and Nest being published this fall by Harvard University Press.

Eloquent Eggs and Disintegrating Dice runs through November 29th and includes special events you won’t want to miss – especially if you enjoy photography:

  • Photograph Behind the Scenes at the Carnegie Museum of Natural History on Saturday, September 27, 1:00– 4:00 p.m.
  • National Aviary Photographic Safari on Saturday, October 18, 9:00 a.m. –11:00 a.m.
  • Egg and Nest: Book Signing with Rosamond Purcell on Saturday, November 8, 5:00 p.m.

The Silver Eye is located at 1015 East Carson Street on Pittsburgh’s South Side.  There’s an opening reception this evening September 24, 5:30 pm-7:30 pm ($5 for non-members). 

For more information, contact Silver Eye Center for Photography, 412-431-1810. 

(photo by Rosamond Purcell.  Click on the image for information on the exhibit)

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Sep 22 2008

Kettles

Hawk and vulture kettle, Cardel Mexico (photo by Powdermill staff)No, I don’t mean pots and pans.  I’m talking about hawks.

Hawks form “kettles” in thermal updrafts during migration.  When they find a column of warm, rising air they stretch out their wings to rise with it.  Other hawks see the kettle forming and join the crowd.  The kettle grows and grows.  

As each hawk reaches altitude at the top of the thermal he sets his wings and glides away toward his destination.  One by one, birds leave the kettle from the top while others join below.  During their glide hawks lose altitude so they find another thermal and repeat the process.  Perhaps this “boiling” action is why it’s called a kettle.

Kettling saves energy because the hawks rarely have to flap.  They also save by migrating along mountain ridges with the wind at their backs.  For that reason hawk watches are located on ridge tops, the most famous being Hawk Mountain in Schuylkill County, Pennsylvania.

Broad-winged hawks are the champions of kettling.  Last week was the peak of their migration through Pennsylvania and you can see it in the hawk watch numbers.  Take, for instance, these three locations on September 16th:  1,169 hawks reported at Buckingham, 2,905 at Militia Hill, and 2,005 at Rose-Tree Park in Media.   These hawk watches are located in a straight line as the bird flies.  If you’d had a way to mark a group of birds you could probably compute their ground speed using hawk watch records. 

Some days are better than others.  The next day (September 17) Buckingham counted 7,512 raptors. 

And some places are just plain stupendous.  Veracruz, Mexico saw 66,223 raptors fly by yesterday.  64,917 of them were broad-winged hawks – and they haven’t reached their peak yet!  

The miracle of the Veracruz “River of Raptors” is an accident of geography.  By the time broad-winged hawks reach Veracruz on their way to South America, their entire population is concentrated in a narrow flyway along the Gulf Coast.  The kettles there contain thousands and thousands of birds - broad-wings, turkey vultures and others – as pictured here at Cardel, Mexico by the Powdermill Avian Research staff in October 2006. 

I remember the thrill of seeing small kettles at the Cadillac Mountain Hawk Watch this year.  Some day I hope to see the huge kettles… but it will have to wait until I have time to make the trip.

p.s. For daily reports and monthly summaries of hawk counts in North America, see the Hawkcount website.

(Thanks to Bob Mulvihill for providing this photo from Powdermill Avian Research.  Click on the photo to read about their trip to the 2006 NAOC conference and Cardel, Mexico.)

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Sep 20 2008

Monarch Migration

Monarch butterflies, one showing tag (photo by Marcy Cunkelman)As I write this, eastern monarch butterflies are migrating south to Mexico, a journey of 2,500 miles for those who hatched in Canada.

What makes such a small, delicate insect travel so far?

Insects have a variety of strategies for surviving the winter.  Some overwinter as eggs, others as larvae underwater, in cracks or in mud.  Some adults hibernate and just a few – including monarch butterflies – migrate.

Unlike their spring and summer ancestors, the monarchs who emerge from chrysalids in the fall don’t breed.  Though they look like adults, the shorter days and cooler nights delay their sexual maturity.  Instead, they migrate to twelve mountaintop sites in Mexico.  Then in March they travel a short distance north and breed.  Succeeding generations live 2-6 weeks and also fly north so that several generations later our first spring monarchs arrive in late April.

How did people figure out that monarch butterflies migrate?

It took over 40 years of tagging and tracking monarchs before Dr. Fred Urquhart found their wintering site in 1976.  Even then it was kept secret for a while because the scarcity of sites makes the population vulnerable.  Nowadays the wintering sites are eco-tourism destinations where visitors can observe millions of butterflies in the Oyamel fir trees.  You can also participate in tagging and tracking programs here at home.

My friend Marcy Cunkelman has been tagging monarchs for many years.   Similar to bird banding, monarch tags are uniquely coded stickers applied to the butterflies’ wings.   In order to collect monarchs Marcy designed her garden to be attractive to butterflies.  In her photo above you can see a cluster of four of them on her butterfly bush.  The one on the left is showing its tag.

Marcy’s monarchs have traveled far.  In 2003 she learned that one of her butterflies was recovered in Mexico.

Thanks to the Internet, you can watch the monarchs’ migration and find out how to participate in the tagging program yourself at the Journey North and Monarch Watch websites.

p.s. I saw a lot of monarchs migrating on the Sept 14 before Hurricane Ike came to western PA, then none until today.  I think a lot of butterflies died during the wind storm.

(Marcy Cunkelman also teaches hands-on programs on monarchs and butterfly gardening.)

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Sep 18 2008

What’s this cloud on the ground?

Published by under Insects, Fish, Frogs

Funnel spider web (photo by Kate St. John)Or is it a galaxy?

Actually it’s a funnel spider web exposed by yesterday morning’s fog. 

Funnel-web spiders (Agelenidae) build a wide web with a central hole.  The spider hides in the hole waiting to feel the vibrations of an insect walking on the surface.  When he senses prey on the web he darts out, bites the prey and drags it back into the funnel to eat. 

The first time I ever saw a funnel web was on a foggy morning in Maine.  I immediately guessed that a spider was in the hole so I gently tapped the flat surface of the web with a long twig.  The spider looked out to see what was happening but my tapping was not gentle enough to fool him.  He retreated and refused to come out when I tried again.  

Fortunately funnel-web spiders in North America are harmless so it wasn’t dangerous for me to experiment like that.   Don’t try this trick in Australia!

(photo by Kate St. John)

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Sep 16 2008

If a tree falls in the forest…

Fallen tree (photo by Kate St. John)…does it make a sound?

You bet it does!

On Sunday night, as the remnants of Hurricane Ike passed through western Pennsylvania, too many of us heard the noise of falling trees.  No rain fell but the wind gusted from 65 to 79 miles per hour.

Just that afternoon I had hiked the Glacier Ridge Trail at Moraine State Park.  At that point the weather was already unpleasant - 86 degrees and humid with winds over 30mph.

In the distance I heard the crack of a rifle shot, then several rapid shots followed by the sound of cannon.  It wasn’t gunfire.  Somewhere out of sight, a tree fell in the forest.

I was lucky I wasn’t close enough to see that tree fall.  When we were in Maine I learned about widow makers from my cousin John.  They’re dead limbs that are about to fall or have fallen partway and are hanging overhead.  Just a touch of wind is enough to send them hurtling to the ground.

Now that I knew what I was looking at, these trees over the trail made me nervous.  (I took their picture anyway).  The stronger the wind got, the sooner I wanted to be out of the woods so I picked up my pace.

Later that night when the wind howled against our house I wondered about the flock of wood thrushes I’d found in a thicket near these broken trees.   I hope they made it through the storm.

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Sep 15 2008

Night Travelers

Published by under Migration

Across the continent thrushes are on the move.  Swainson’s, wood thrushes and veeries are all heading south.  They travel at night.

When the weather is clear with a light north wind their urge to leave is strong.   They begin their flight half an hour after sunset, using the earth’s magnetic field and the infrared glow of the western horizon as guides.  If all goes well they stop before dawn in a place with abundant food and shelter.

As they fly, the thrushes call to each other to keep the flock together.  Each species has a unique flight call so if you know the sound you can identify them in the dark as they pass overhead.  Unfortunately it’s not quiet enough to do that where I live in Pittsburgh but we could hear them in Maine.

One night in Bar Harbor is especially memorable.  My husband and I had left a restaurant and were strolling along the waterfront when I heard thrushes overhead.  By the light of the street lamps I was able to see them coming in low over the bay and passing overhead only thirty feet up.  On and on they came, heading due south over the island. 

It was such a thrill to finally see the night travelers.  We think of them as “our” birds but they are actually nomads.

(This photo of a Swainson’s thrush was taken during spring migration by Chuck Tague.)

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Sep 13 2008

Like an Arrow

Published by under Water and Shore

I see my favorite sea bird twice a year because I migrate to the same places he does:  Maine in September and Florida in February.  

Gannets are huge birds with a 6.5 foot wing span and pointy wings, bill and tail.  Related to boobies, whom they resemble, gannets eat fish and squid along the continental shelf on both sides of the North Atlantic.  Not only do they nest communally, but they hunt in large flocks when they discover that predatory fish have forced their prey to the surface.

My favorite part about northern gannets is the way they hunt. 

Gannets fly into the wind looking down for prey.  Because of their long pointed bill, their bodies look like upside down checkmarks from a distance.  Thirty to 130 feet above the ocean, the gannet spies a fish and begins his head-first dive making his body and wings into the shape of a W.  Just before he hits the water he straightens his wings tight against his body and enters the water like an arrow.  Gannets dive at speeds exceeding sixty miles per hour so they have air sacs in their faces and chest which cushion the impact like bubble wrap.

Northern gannets nest colonially on island cliffs, principally in Scotland, Ireland, Norway and Canada.  They lay one egg per year and incubate it by covering it with their webbed feet.  They feed the nestlings by regurgitation, flying up to 300 miles in search of food.

When young gannets leave the nest they weigh 50% more than their parents and have fat reserves that last one to two weeks.  That’s because they are completely on their own and too heavy to fly up out of the water in their first few days after fledging.  Instead they immediately begin migration by swimming southward, learning to hunt and fly as they go. 

They’re on their way from Canada now.  I’ll see them in Florida in five months.

(photo by Chuck Tague)

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Sep 10 2008

Bug Migration

Back in 1990 no one knew if dragonflies migrated but they thought it might be true. 

Every fall people noticed dragonflies flying the same flight paths on the same prime migration days as the birds.  They even saw them traveling west along the Gulf coast from Florida to Louisiana.  Were they going around the Gulf?  Were they migrating south?

In 1992 a group of scientists initiated the North American Dragonfly Project and asked observers to record dragonflies moving along the coasts and at hawk watches.  Their hunch was correct.  Twenty-five to fifty of the world’s 5,200 species of dragonflies do indeed migrate, though we still don’t know where they go.  Common green darners, pictured mating by Chuck Tague, are one of them.

Just as with monarch butterflies the individual common green darner who flies south is not the one who makes the return journey.  In the spring that individual flies a short distance north, mates, lays eggs and dies.  Her offspring emerge and fly further north repeating the process.  Eventually the insects reach the northern limit of their range, the season changes and their descendants head south.

I always see dragonflies at hawk watches.  They’re the fighter jets of the bug world, very quick and highly maneuverable.  When flying ants plague us (what is it with flying ants at hawk watches?) the dragonflies make mincemeat of the ant swarms.  My favorite insect moment was when, through binoculars, I saw a dragonfly zoom in and chomp a flying ant in mid air.  Good show!  On the other hand I’ve seen American kestrels snatch dragonflies from the sky and eat them in flight – a sort of snack “to go.”

Such are the perils of migration.

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