Sunday, June 19, 2011

Summer Skimmers

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     I guess The Creator had a lot of niches to fill, but flying over the surface of the water at speed to catch little fish seems an improbable one.  Indeed, how often have you seen a skimmer that has actually caught something?  The Black Skimmer (there are two similar species, one in Africa, one in Asia) is well adapted to do this job.  First of all, the birds know where to fish.  They are so mobile that they can search large areas for concentrations of small fish forced close to the surface by evaporation or tides.  They even hunt for fish or invertebrates temporarily washed onto beaches by wave action. They have one huge advantage over terns.  Since skim-fishing is a tactile, not a visual activity, they can fish at night.  Schools of little fish often rise to the surface at night.  Doesn't sound like such a silly hunting strategy any more.
      Another feeding adaptation these birds have is their hugely long wings.   When you are flying an inch or two above the water, you can't produce a full wing stroke. Forty five degrees of movement is all you get.  It's like running with your legs tied together. So the extra lift provided by their length is necessary.
      Of course the beak of a skimmer is its most obvious attribute, but look at it head on (at 13 seconds in the video).  It's a knife edge offering very little resistance to the water.  Babies are born with both mandibles equal in length, and do not look "skimmery" until they fledge.  Here are some shots made at a rookery and beach on Marco Island, Florida.

Tuesday, June 14, 2011

A Spruce Grouse Tale (Tail)

We birders today are so obsessed with identification that many of the things that birds do go right past us. Not so with the old-timers.  Sometimes it's fun to go into the old literature and read accounts of birds written before the age of field guides and scopes. Ordinary people would publish their observations right in the scientific literature.  The best compilation of all this stuff remains "Life Histories of North American Birds" by Arthur Cleveland Bent.  In the 1960s Dover Publishing produced a paperback edition of these 20-odd volumes, so they are easily found.  Some have even been put online.

I had shot some footage of a male Spruce Grouse and decided to see what Bent said about it. He reported a ca.1890 account by a Nova Scotia scientist and photographer named Watson L. Bishop. Here is what Mr. Bishop said:

"The red comb over each eye is enlarged until the two nearly meet over the top of the head...While he is strutting, the expanded tail is moved from side to side.  The two center feathers do not move but each side expands and contracts alternately with each step as the bird walks...This attitude gives him a very dignified and even conceited air."

You won't find a description like that in Sibley!  Anyway, here's the bird, slowed down 50%.

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Flat-footed Flicker

Flickers spend more time on the ground than most other woodpeckers, hunting for ants.  You'd think that after millions of years, they would have developed some grace about it, but not so.  Watch this Northern Flicker negotiating a paved road.  I've slowed it down by half.  It moves like a three year-old with his fathers's heavy shoes on, kicking forward with each step, slipping and sliding along.  I can't think of any other ground-living bird that moves like this, yet there is something familiar about it.
What's so familiar? Beak pointing forward and up, tail raised, then lowered upon stopping, a hop with both feet off the ground at once and grasping  forward for purchase.  It's exactly how a woodpecker hitches up a tree, but here it's horizontal.  No wonder it's so ungainly.  He's trying to climb the sidewalk.  But give this bird a chance.  There is still hope.  The Andean Flicker, which spends almost all it's time on the ground, has learned to walk.

Sunday, June 12, 2011

Head movements in terrestrial birds

     Wow, really sounds scientific.  I was reviewing some footage of a Solitary Sandpiper, and couldn't help being struck by the way the bird would move it's head back and forth while looking at me.  We've all seen this millions of times.  I've always written it off as a nervous movement prior to taking off or running away.
Turns out there may be a better explanation. (Not mine, I read this.)

       Many birds, shorebirds for example, have their eyes situated to get the best view in as many directions as possible at once.  Thus the eyes are set high on the head and on opposite sides. One eye looks north, the other, south. Unlike raptors, binocular vision is impossible.  No binocular vision means lousy depth perception.  So how do you tell how far away that guy with the camera really is.  One possible way is to take your one eye (the one on the side where the guy is) and move it a short distance.  If your brain is capable of taking the image from head position 1 and that from head position 2 and combining them, you get a 3D image...just like 3D glasses.  Voila, depth perception! Up and down, side to side or something in between doesn't matter.  Can a bird's brain do this?  I don't know, but for an organ that can sleep one side, while the other is awake (as in long-distance migratory flights), it seems like a trivial task.

Saturday, June 11, 2011

Snap, Crackle, Pop

     I hated Rice Krispies as a kid.  You had to wet them with milk for them to do their snapping act, and they got soggy so fast that the audio fun was eclipsed by culinary mush.  Not so with Manakins.  They can snap all day long.
     As is obvious from the two previous entries, development of this blog was inspired by a trip to Panama.  (There will be plenty of North American stuff later). One of the target groups on this trip was the Manakins (Pipridae).  Manakins are sparrow-sized birds, not related to the Nutmeg Mannikin, which seems to be popping up all over the US and elsewhere.  Male manakins are brightly colored, and they "dance" in leks.
You've probably seen video of one or another species doing the Michael Jackson "moonwalk".  I was fortunate to have Carlos Bethancourt of Canopy Tower lead me to where Golden-collared Manakins were displaying.
     The males are pretty, yellow and black, with yellow neck feathers that stick out parallel to the beak when they are in display mode.  But the amazing thing about these birds is the sounds they make.  Golden-collars are pretty basic, with whirrs and snaps, but the snap is so loud that some people jump or gasp when they hear it for the first time.  I sure did.
     Unfortunately my humble video can't show how this snap is produced, but you can tell it is wing-driven. Here is a brief clip of a snapping manakin. These are called "roll snaps". You hear two sets of two rattles.  Each rattle is made up of 8-10 individual snaps.  Individual snaps are 20 milliseconds apart.

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In 2003 Kimberly Bostwick and Richard Prum of Cornell University published high speed video of a White-collared Manakin doing it. You can see that the wings are beating against each other at about 50 beats per second.  I was confused when my video (slowed down) showed a snap sound coming from the bird at a time when the wings were obviously not touching.  Turns out that it happens so fast, that the wings were indeed already apart before the sound travelled the 7 meters or so to my microphone.  It's still hard to understand how feathers hitting each other can make such a loud snap.  Even Bostwick and Prum weren't exactly sure if there was something else involved.  If these birds' parents aren't around, maybe they're cracking their knuckles. Do old manakins develop arthritis?

Fellow traveller

This is another hummingbird post, indeed also about the White-necked Jacobin.  I thought, when I saw this that it represented one of the flower mite species which live in flowers, compete with hummingbirds for the nectar (apparently they exist in huge numbers), and ride the hummingbirds to get to their next flower.
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Upon close examination, however, this seems to be just a little spider.  She's probably still hitching a ride.

Seeing birds in a new way

     Did you know that hummingbirds drink with the backs of their heads?  I didn't either until I shot this video.  It's a fine example of the sorts of subtle behaviors, plumages, and details of a bird's life that only video (or motion pictures) can capture.  I have been doing this for a lot of years, and decided it's finally time to put some of this stuff out where others can see it.

     As a first entry to this blog, here is a hummingbird.  This is a White-necked Jacobin, a bird common in Central and South America.  It was filmed at the Rainforest Discovery Center in Soberania National Park, Panama.  You may wonder, as do I, what is a Jacobin?  The term refers to a political group, active during the French Revolution.  Since this bird was first described in 1758, it is easy to see why a French Revolutionary name might have been ascribed to it, after it became known outside of scientific circles.  The best-known Jacobin, the infamous and deadly Robespierre, presided over the french Reign of Terror.  Since this rather large bird easily takes over whenever it appears at a feeder, one can see why it might have been named after that feared lopper of heads. There is also a breed of fancy pigeon called Jacobin.  Anyone know the real reason for these names?

     Anyway, watching this video, one is struck by the pulsation of the birds head as it feeds.  Is this some kind of suction device?  Turns out that it isn't.  Hummingbirds do not drink nectar like through a straw. They lap it up, like a dog or cat when there is plenty (at a feeder), or let it ride up the tongue by capillary action when ther isn't much (at a stingy flower). To feed, the tongue has to be extruded, and this is why the head pulsates.  A hummingbird's tongue is attached to muscles that run from the mouth, around the base of the skull, up the back of the head, over the top and finally end somewhere near the eyes.  These long muscles allows the tongue to stick out far enough to get at the nectar.  The pulsations you see are simple the flexing of the muscle.  Nectar is not sucked up into the rear of the head, like it may at first appear.

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        This clip has been slowed down 8 times.  You can see that for each flex of the muscles at the back of the head, the bird actually swallows as the tongue is brought back in with its load of nectar.  The rate in real time is 7 per second.