Friday, September 19, 2014

The Way You Move Ain't Fair, You Know.

     I recently had the pleasure of watching an Ovenbird, a Swainson’s Warbler and a Northern Waterthrush feeding on the same patch of ground as fall migration heats up here in South Florida. The feeding techniques of the three birds are distinct. The Ovenbird struts about like it owns the place and picks up food along the way. Swainson’s Warbler hops and scratches, always staying hidden under one branch or the other. The Waterthrush scratches too, but shows a characteristic bobbing motion of its nether parts as it moves about. And that is the subject of this note.

     There are several birds that bob as they walk, or even while standing. In North America the Spotted Sandpiper comes to mind. But there are others too. The waterthrushes, American Dipper, and Solitary Sandpiper all do it.  The biggest bopper of all is the Wandering Tattler. World-wide other related birds bob. Bobbing is not to be confused with tail flicking. Wagtails and pipits mostly tail-flick. So do a number of flycatchers. Bobbing involves moving more than the tail feathers.  Why birds do this has never been determined, and rarely studied, even though many have commented on it in the literature. There are lots of explanations:
  1. It flushes insects as they walk.
  2. It’s camouflage, as most of these birds spend time near running water. Predators have trouble seeing the bouncing bird next to the babbling water .
  3. It helps the bird visually, like head nodding in a pigeon.
  4. It’s signaling to a mate or companion.
  5. It’s territorial dominance display.
  6. It burns off nervous energy.
  7. It helps digestion by moving the food along the gut.  Like going for a jog after Thanksgiving dinner. 
  8. It’s a predator deterrence signal, telling predators  “I am so fit that I can waste effort doing this. You better go chase someone weaker”. Thompson’s Gazelles leap into the air (pronking) for the same reason.

All of these explanations have shortcomings.
  1. These birds eat a lot of buried prey that doesn’t respond to flushing.
  2. Any predator that can’t tell a bird from water needs to become a vegetarian.
  3. The heads in bobbing birds remain perfectly steady and are not affected by the bob at all.
  4. With the exception of wintering pipits, these birds tend to be solitary.
  5. This explanation is more believable, as juvenile birds are less vigorous at bobbing . A video by Don DesJardin shows an adult Spotted Sandpiper bobbing while tussling with a younger bird, who is not.
  6. This is absurd, as new hatchlings bob from day one. They have no energy to waste.
  7. I couldn’t find enough Scolopacid gastroenterology literature to investigate this.
  8. This is an attractive hypothesis, especially considering that the rate of bob increases as danger approaches. It does not explain why Spotted Sandpipers (video by Hector Ceballos-Lascurain) and Wandering Tattlers (video by Don DesJardin) feeding on the beach bob little, if at all.
      I endeavored to find alternative explanations, and so began reviewing my video of various shorebirds for clues to why some of them bob, and others do not. It quickly became apparent that bobbing happens with a slow walk, but not with a run or a dash. Bobbing almost always accompanied picking ones way through sticks, trash, over rocks or logs, and wading in shallow muddy water. Not so much on the beach, and certainly impossible while immersed at dowitcher depth. Bobbing in both Spotted Sandpipers and Wandering Tattlers involves the whole torso and occurs at a rate of 2-3 per second. Activity so energy consuming must be very important.

      Slow motion video of a Spotted Sandpiper revealed that at the top of a bob, the rearmost leg is pulled up with the body, after which it is carefully moved forward. Could bobbing be a means of preventing trips, stubs and possibly worse injury while walking on uneven terrain where grass, mud or dirty water prevents seeing where you are stepping? Snagging a toe on a rootlet could be dangerous. Assuring that your foot is fully out of the soup before trying to move it forward sounds like a good idea. Think of how you walked the last time you tried to negotiate a mangrove swamp or river bottomland. You raise your feet all the way out with each step. Think of the injured birds you have seen. Many of the injuries are foot injuries. Anything that could lessen this would be of value.

     This reflex may have added benefits while in thick mud. The constant up and down motion transmitted to the feet makes it less likely that toes become mired in tenacious muck. When the neighborhood Merlin is in a stoop at you, the split second gained by having your feet relatively free at takeoff can be a lifesaver.

        WanderingTattlers (video by Don DesJardin) don't fit the Spotted Sandpiper model. Their bobbing is more constant, steadier in its amplitude and doesn't seem to affect the movement of the legs. This very old video of a tattler walking in a creek gives the impression that the bird is doing all it can to maintain its footing on the jagged stones. Could tattler bobbing be related to balance? The idea is not that far-fetched. If you have ever played with a gyroscope, or repaired a bicycle wheel, you know that a rotating wheel tries to maintain its vertical orientation. This is why you don't fall over when you ride a bike. A bobbing tattler is not a wheel, but it is a pendulum. It swings back and forth with an amplitude of about 6 centimeters, at a rate of 2 swings per second. The fulcrum (pivot point) is at about the lesser coverts, making it more like a seesaw than a sideways pendulum (as the tail goes up, the “shoulders” go down). The resulting movement creates angular momentum, the force that keeps the bicycle wheel steady. Yes, it must be very small. This is a bird, not a bicycle. But a small steadying force might give the tattler just the stability it needs to find its footing and negotiate treacherous terrain. It is of interest that in videos, Wandering Tattlers feeding on sandy beaches do not bob much, if at all. Balance then on a rock, or put them in more uneven ground and the bobbing is easy to see.

        I certainly don’t advance these speculations as a definitive explanation for bobbing behavior in birds. They do, however, point out once again, what you can learn about birds from watching video.


Wednesday, July 4, 2012

July 4, 2012 In conjunction with UWOL 23, here is an explanation of FOCUS STACKING for video.

Focus stacking is a wonderful technique to allow both the foreground and background of a photo to be in focus. Although these days everyone goes "gaga" over those out of focus backgrounds, there are still people who like to see the background in focus. It adds depth and realism.

You can do this in video. It’s more difficult than with a photo, but very effective under the right conditions. The conditions are:

1. No wind (or very little). A breeze may be too much.

2. A solid tripod. Clamp down the tilt and pan. No camera movement allowed.

3. A clear view of what will be background with no foreground elements in the way, and vice versa. This takes very careful positioning of the camera.

Many shots you want to take just cannot comply with this rule. Find another shot.

4. A buffer zone. Between what will be the focused foreground and focused background, there must be a small space that will remain unfocused. This can be blue sky (the best), sand, gravel or dirt, grass, still water, rapidly moving water (like a waterfall), busy leaves, branches or bark…anything bland enough not to be noticed that it isn’t really in focus. There can be no action in the buffer.

5. Minimal movement of your foreground subject. If it moves too much it will cross the buffer zone and get visibly cut off.

OK. You have found a subject that fit’s the criteria. Now focus on the foreground and shoot some video. Next, focus on the background without moving the camera and shoot some more video, about the same length clip. If you are lucky in your composition, it may be possible to shoot a mid-range clip as well to get that tree that just isn’t quite sharp enough in either the foreground or background.

The rest is done at home. Most video editor software has garbage mattes. These allow you to blot out whole areas of scenes. They are usually used with green screens to superimpose people over landscapes but they work here too. I use Adobe Premiere which has a 4 point, an 8 point and a 16 point garbage matte. The 16 is usually needed. Load the background-focused clip. With those 16 points, outline the background trying as much as possible to keep the border you are making inside the buffer zone (step 4, above). The unfocused foreground will be black…gone.


Now load the foreground-focused clip and do a similar maneuver, outlining the foreground, and blotting out the unfocused background. Try to simulate the path of the garbage matte to the one you did for the background. Now you have two clips with only focused material showing. Superimpose them. Adjust the mattes so no black is showing. Soften the borders (remember these are in purposely unfocused areas, busy spots or edges of things where a border is not likely to be noticed), and there it is.

The technique is not perfect. A sharp eye can see where unintended unfocused material could not be matted out due to movement of the subject. In my UWOL 23 video, pause at the Siamang (the ape) clip or the pelican clip and you can see the errors around their heads. In a moving video this is not likely to be noticed.

While filming be very careful of the wind. Your tolerances of where things are placed are so close that even a little breeze waving a blade of grass that you don’t even see in the viewfinder will ruin the whole scene. Of course if you have a good wide buffer, the wind is less of an obstacle.

This technique is fun to do, and occasionally when you are out, you will run into a situation that just screams FOCUS STACKING. When it does, take a few minutes and shoot it. You’ll be glad you did.

Thursday, March 22, 2012

What is this avocet eating?


American  Avocets feed  by walking through the water and waving their beaks side to side.
Rarely can yousee what it is they are catching.  It's easy to assume that they roil the mud
and grab little critters that are buried.  But not this bird.  It actually caught a wriggling fish.
Slow-motion video shows it pretty clearly. Stop action  shows even more.  The last few
frames are sequential stills.  As the bird shifts the slippery fish closer to its mouth, it can
keep the tip relatively closed.  Notice near the end that the tip is actually  more
tightly closed than the base, and the base of the maxilla (upper jaw) bows upward to
accomodate the fish. This is exactly like a pair of jointed human fingers would have done
 the job. Quite a versatile tool.  And to think that old Count Buffon considered the avocet's
beak to be a degeneration.
To see this clip in high definition

Saturday, September 24, 2011

Small Shorebirds Do It, Too

I have seen on many occasions, larger shorebirds with long beaks, flex their beak tips. It was surprising, but in a way it made sense with a long beak.  Sort of like the old days in the general store when the grocer would grab a can from a high shelf with a long stick bearing a forceps at the end.  I never figured that smaller shorebirds could do it, too.  This sanderling can.  Why?  Maybe it's a good way to keep from getting a mouthful of sand when your beak touches a buried prey item.

Saturday, July 16, 2011

Who was Ludlow Griscom?

     Most birders today don’t have a clue who he was. They may have heard of the Ludlow Griscom Award, given by the American Birding Association annually to someone who has advanced regional birding. But who was the man?  In short, he was the guy who popularized binocular birding. He wasn’t the first, but he did a lot to get the shotguns put back in the closet, and teach people how to identify birds using field marks instead of keying out morphology. He pioneered the use of scopes and was one of the first  to lead organized birdwalks of people not just his immediate friends. He was active from 1910 to the 1950s. Trying to keep this short. For more, see below.

More About Ludlow Griscom

     With a name like Ludlow Griscom you might expect a man to be an upper crust Northeasterner, and you’d be right. His people may not have been on the Mayflower, but they weren’t far behind. He grew up in New York, and once his name was made, moved to Boston. Strangely, the professor never got a PhD. He published extensively in the scientific literature, not only on birds, but actually even more in botany.

     If you are over 50, and didn’t know Griscom, you probably knew someone like him. Totally the professor, never casually dressed, always in control, always the boss, a bit prickly…you didn’t cross him if you were an underling. One colleague called him “the only man I know who can strut sitting down”. And he was only 5’8”. But this guy knew his birds. He made snap IDs of fly-overs, or glimpsed birds, and was always proven right. He didn’t suffer fools or lazy people, but loved to teach newcomers. Perhaps his worst trait, unfortunately a sign of his times and upbringing, was a vocal disdain for certain ethnic and religious minorities.

      He was one of the few professional ornithologists to recognize the important contribution that amateurs could make in describing their own local fauna and flora. He insisted that birders learn their local birds (including migrants) cold before venturing opinions about birds elsewhere. This is why his name is associated with an award for regional birding, and in those days of flivvers and dirt roads, insisting that amateurs stay home and become local experts may have made sense.

     We have come a long way since the birding days of Ludlow Griscom. Today we stand on the shoulders of giants. Griscom, who Peterson went to when he couldn’t identify a bird, was certainly one of the biggest.  To learn more about this giant of birding, go to the Raven On The Mountain Video Channel 2 and watch "How Many Birds Do You Need" parts 5 and 6.

Saturday, July 9, 2011

Red Knots in a Big Bind

for a higher definition view

    I try to stay off the soapbox in this forum, but today has to be an exception.  A report appeared this spring on the population of Red Knots wintering in Tierra de Fuego.

Among its conclusions were that the number of Red Knots of the rufa subspecies in Tierra del Fuego had fallen from 16,000 to 11,000 and that the TOTAL population of  rufa was 25,000. This subspecies (Calidris canutus rufa) is the Red Knot that we see on the east coast of the US, and apart from some birds of the roselaari subspecies that join them in Florida, it’s all we have.  It may be true that the Red Knot can be found worldwide, but for most US birders, rufa  is the ballgame.

Now 25,000 may sound like a lot of birds.  It isn’t.  Consider that the population of rufa Red Knots in 1992 was 150,000. We now have lost 5 out of 6 birds.  Consider that in 1893 a group of hunters shipped 4000 Red Knots from Cape Cod to Boston in barrels after one night’s shooting.  Consider that in the 1920s, ornithologist Alexander Sprunt tried to shoot one Red Knot flying by (for a museum display) and they were so thick that he accidentally got thirteen. That’s how it was.  Now there are 25,000, period.  The decline may not be on the same scale as tigers or rhinos, but it is constant, and the reason is the same…desire.

I think that most birders bemoan the disappearance of the Eskimo Curlew, a wonderful shorebird with a mournful call that added to the ambiance of being on an autumn windswept beach in New England, and which brought the bright days of spring to Midwestern farms.  No more.  These trusting birds were hunted to death.  That was in the days of our great-grandparents.  If we could only bring them back.  The Red Knot is today’s Eskimo Curlew, and we can keep it from becoming our children’s regretted loss.

A lot of migratory birds are hunted along their routes.  Shorebirds, in particular fall to guns in places like Barbados, and certain areas of South America.  It may be a bit comforting to be able to blame “backward countries” for their barbarism in diminishing our birds, but for the Red Knot the enemy is us.  Red Knots have the unfortunate habit of depending on very specific areas during migration.  More than most birds.  Their most important one is Delaware Bay.  Here, for a few days in May, they gorge on the eggs of horseshoe crabs, laid in the sand of the beaches.  They get fat.  They fly on to the shores of the Arctic Ocean to breed.  Or at least they used to. Horseshoe crabs are now hard to find in Delaware Bay.  The birds leave hungry and weak.  They can’t sustain a decent breeding effort in the Arctic.  No kids for enough years and the population plummets.  That is the story of the Red Knot.

So what happened to the Horseshoe Crabs?  Back in the 1970’s when I used to go to Port Mahon, Delaware to see the knots, people drove garbage truck-sized vehicles along the beach and collected crabs by the truckful.  They said it was for fertilizer.  Today the problem is sushi.  People don’t eat horseshoe crabs, but it is widely used as bait in traps to catch other seafood. The best known is the Unagi (eels) that millions of people worldwide enjoy in sushi bars every day.  Just like the penises of tigers, and the horns of rhinos, the lives of crabs and knots are forfeit so that people can have their delicacy du jour.

And of course, efforts by the states of New Jersey, Delaware, Maryland and Virginia to limit the crab harvest rapidly become mired in jobs, jobs, jobs.  It’s a worn out story.  So what is the solution?  Make the Japanese give up their evening eels?  Seed the beaches with caviar during mid-May?  Birders screaming at officials is probably the best bet.  One thing is certain.  If birders don’t lead the way, then we will see the disappearance of a creature not hidden in some southern swamp, but on the beach right in front of our eyes.  Or maybe just hop a plane to Alaska.