Showing posts tagged birds

Dunlap, K. and Mowrer, O. H. (1930). Head movements and eye functions of birds. J. Comp. Psychol. 11, 99–113.

People make a lot of hay out of the series of photographs by Eadweard Muybridge that Governor Leland Stanford commissioned to figure out whether all four hooves of a galloping horse are airborne at the same time. Muybridge ingeniously used an array of cameras that were triggered sequentially by the horse busting through a series of trip wires. The result of this experiment was that there was definitely a moment in the horse’s gait when all four feet were off the ground. (Stanford went on to found the university that produced Olympic water polo player Tony Azevedo; Muybridge ended up shooting a man who slept with his wife, but was acquitted on grounds of “justifiable homicide”.)

Now I don’t want to dump on the birth of cinema, but I’ve just been out watching horses gallop around all morning, and I’m pretty sure that I could reproduce Muybridge’s experiment with some study drugs and a mug of properly mulled cider. Things are always clearer in hindsight, but it didn’t take much squinting to convince me that horses are airborne every quarter second or so. Perhaps Muybridge and Stanford were half blind from living in an era before proper sunglasses, or maybe horses were faster in the 19th century because there were no clocks and all the conductors had to count continuous Mississippis to keep the trains on time.

Whether or not the Muybridge horse study was necessary, subsequent developments in rapid picture-taking have proven incredibly useful for the study of biomechanics. Today I want to discuss an early example of how the camera can be used to compensate for the inability of us humans to fully appreciate animals. 

Many people have wondered, “What’s up with pigeons bobbing their heads all crazy while they walk”, but most people are too afraid to blog about it. As Dunlap and Mowrer, the authors of today’s sick pape, put it, “The forward and apparent backward movements of the head which pigeons, chickens, and certain other fowls display while walking have been commented on by various persons orally, but seldom in print.” 

It may have occurred to you that this jerky head movement is an accident of the pigeons walking gait, perhaps analogous to the swinging of a human’s arms. But this is wrong. In 1930, Dunlap and Mowrer took some great photos that proved that bird head bobbing is just an illusion. In fact, it is you, the viewer, who is lurching ferociously back and forth, and the bird is perfectly motionless! That’s not actually true. What is really happening, Dunlap and Mowrer found, is that when the bird’s body is moving, the head is completely still. In other words, the head is locked in position relative to the forward moving body. Then, when the body stops for a brief moment, the head thrusts rapidly forward to a new position. So, overall, the head is maintained in a stable position relative to the body. The stroboscopic photo above, from a sick follow-up pape by B.J. Frost in 1978, illustrates this nicely.

This head stabilization has obvious benefits for vision, as it is much more difficult to analyze a visual scene when your head is shaking. Another set of experiments by B.J. Frost in the 70’s clearly demonstrated that head-bobbing is controlled by vision, as pigeons walking on treadmills don’t bob at all (because the visual scene is stationary).

The findings of Dunlap and Mowrey in 1930, and subsequent work by B.J. Frost and other enthusiastic bird bio-mechanics, are a superb example of how the world is incredibly fast and confusing, and only photographic magic and detailed quantification can distill truth from all the chaos.

Contributed by butthill

SICK PAPES SPECIAL ON CONTROVERSY: PART 2

Curr Biol. 2010 Sep 14;20(17):1534-8.
The role of the magnetite-based receptors in the beak in pigeon homing.
Wiltschko R, Schiffner I, Fuhrmann P, Wiltschko W.

VERSUS

Nature. 2009 Oct 29;461(7268):1274-7.
Visual but not trigeminal mediation of magnetic compass information in a migratory bird.
Zapka M, Heyers D, Hein CM, Engels S, Schneider NL, Hans J, Weiler S, Dreyer D, Kishkinev D, Wild JM, Mouritsen H.

AND

Nature. 2012 Apr 11;484(7394):367-70.
Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons.
Treiber CD, Salzer MC, Riegler J, Edelman N, Sugar C, Breuss M, Pichler P, Cadiou H, Saunders M, Lythgoe M, Shaw J, Keays DA.

There are some scientific subjects that attract recreational bedlamites like seagulls to a coastal landfill. My favorite of these is magnetoreception: the ability of an animal to perceive an ambient magnetic field. Lots of animals can do this—birds, insects, reptiles— and some of them use the earth’s weak magnetic asymmetry to achieve extraordinary feats of navigation. For example, scientific hero Ken Lohmann has shown that sea turtles navigate thousands of miles through the horrific salty ocean in order to meet their half-shelled-brethren at a specific location for an annual Bacchanalian picnic. Ken’s lab also found that if you move a spiny lobster 20 miles in any direction from its preferred hangout spot, it immediately returns directly to its headquarters using cues from the earth’s magnetic field. These and bajillions of other examples demonstrate that many of the earth’s macro-biotic inhabitants can use a magnetic sense to cruise around in magnificent style, which, in my humble opinion, is absolutely fucking fantastic.

Returning to the bedlamites. There are two dudes in particular that illustrate the fact that magnets exert a certain ineffable force upon the zanier castes of our super-organismic civilization. The first of these is shown in the video above: Mr. Harry Magnet, whose extensive pape on personal perception of magnetic fields cannot be deemed sick or otherwise, because it has not undergone rigorous peer review (but we welcome submissions).

The second example comes from Alane Jackson, the purveyor of a theory called magnetrition, which was first explained to me by a youth soccer referee who lived in a wigwam on an magnetically neutral island in the middle of an Alaskan lake. Basically, Alane’s idea is that mitochondria are magnetically charged, and that jostling our cells around causes cytoplasmic stirring, thereby promoting health. I also recommend another section of Alane’s website, titled Smoking is good.

Buried beneath all of this absolutely essential HTML is an equally intense scientific debate about the mechanisms by which real animals measure magnetic fields. So far, two basic mechanisms have been proposed:

(1) MAGNETITE. The magnetite hypothesis was inspired by the observation that some magnet-loving bacteria produce magnetite (Fe3O4) crystals that cause them to align with and cruise along the local magnetic vibe. Because magnetite has also been found in the snouts/beaks of fish and birds, it was suggested that the rotation of these crystals could be detected by mechanosensory neurons in the brain. Smaller, “superparamagnetic crystals” have also been found in bird beaks. These crystals do not have a permanent magnetic moment, and therefore do not individually rotate to align with the earth’s magnetic field. However, large arrays of these superparamagnetic crystals would attract and repulse each other under different magnetic field conditions, generating forces that could, in principle, be sensed by neurons.

(2) CRYPTOCHROME. This second mechanism is even bonkers-er. Some radical-pair chemical reactions can be influenced by magnetic forces—one example is the absorption of light by retinal photopigments called cryptochromes. The idea is that the ambient magnetic field would alter the rate of cryptochrome photo-isomerization, so that if a bird were gazing upward at a clear blue sky, it could actually “see” a hazy magnetic field image layered on top of the normal visual scene.

The argument surrounding these two mechanisms is best exemplified in the bird magnetoreception literature, which has been enriched in recent years by a flurry of combative pape-slinging. In one camp, (1) the Wiltschkos and their pals claim that birds use little magnetite particles in their beaks to detect magnetic fields, while in another camp (2) Henrik Mouritsen and his pals  claim that magnetoreception arises in the retina, mostly likely through cyptochrome. (3) David Anthony Keays and his buds weighed in on side 2 of the fracas last year, when they suggested that those magnetite particles in the beak are located inside little pieces of biological irrelevance called macrophages.

Although the field of magnetoreception is confusing and controversial, one cannot help but delight in the titillation-level of the questions and the unfettered academic shit-hurling. Magnetoreception is clearly the modern El Dorado, attracting both well-funded academics and itinerant kooks. There is the important possibility that everybody is right— that birds have two independent magnetic senses and so do people, and the booty will be split evenly amongst the Professors and the online gurus. It seems much more likely to me, however, that this entire field is booby-trapped, and that all the magnet-lovers will end up stalking monkeys on a raft as the river below their feet slowly transforms into a cauldron of boiling soup.

Contributed by butthill

Jonathan D. Charlesworth„ Timothy L. Warren, & Michael S. Brainard (2012). Covert skill learning in a cortical-basal ganglia circuit Nature DOI: 10.1038/nature11078

This hump day, we at Sick Papes bring you an exclusive heart-to-heart poolside chat with Jonathan Charlesworth, the author of a hot-off-the-press pape that was described by one of our Sick Papes interns as, “so-sick-it’ll-make-your-antiobiotic-resistant-staph-infection-feel-like-a-sensuous-spaghetti-squash-rubdown.” Currently AOP in the journal Nature, Jonathan’s pape investigates the neural mechanisms of trial-and-error song learning in the adorable Bengalese Finch. Along with his eminent co-authors, Tim Warren and Michael Brainard (both reportedly expert tele-skiers), Jonathan found that LMAN, a region of the bird brain which was previously thought to contribute to online behavioral exploration, can still drive song learning even if its output is inactivated during training. Confused? Just read the goddamn interview:

(SP): In your pape, you demonstrate how blocking the output of the anterior forebrain pathway (AFP) prevents gradual song learning, but when AFP output is unblocked, the learned behavior suddenly appears.  That’s a fantastically trippy and completely unexpected result. Did you design the experiment to test this possibility, or did you just stumble across it?

(JC): We designed it to test this, but we expected the opposite result (i.e. no learning).

 (SP): It seems intuitive that motor learning develops gradually over time, building upon previous learned experienced. For example if I wanted to become a bad-ass skateboarder, I would have to learn how to stand on the board without falling over before I could pull off a kick-flip. But your data suggests that gradual online learning is not necessarily required. Does this mean I should dive directly into the half-pipe? Or do you think that the effect you describe applies only to the initial stages of very basic motor learning?  

(JC): Our results suggest that (if the output of your basal ganglia is blocked), you can learn to select the best of whatever behaviors you initially could generate.  So, if you are always terrible at skateboarding (as I suspect you are), then you will not improve.  However, if you are sometimes terrible but occasionally do well, then you might be able to learn to produce those good performances more consistently.  In our birds, they were already very good at song but performed that song in slightly different ways; after training with the output of their basal ganglia blocked, they learned to produce the “best” version of that song more consistently (where we define best based on our experimentally-imposed threshold for receiving  reinforcement).  We at the Brainard lab in no way endorse diving into half-pipes or inactivating the output of your basal ganglia at home.

 (SP): It was shown in a previous sick pape that when LMAN (the output nucleus of the AFP) is inactivated, song variability decreases dramatically. This suggested that LMAN is actually injecting noise into the song production pathway, then monitoring the outcome in order to fine tune the song. How does your result that song learning occurs independent of constant LMAN output affect this interpretation?

(JC): Our results suggest a more detailed model.  Our results indicate that another source (other than the AFP) is injecting noise into song that can also be used for learning.  We think that this source is within the song production pathway itself.  Our results suggest that LMAN monitors the outcome of both sources of noise in order to fine tune the song.

 (SP): All of your experiments were done in adult birds. What do you think would happen if you silenced the output of LMAN throughout development, and then turned it back on during adulthood?

(JC): Since we think this is limited to trial-and-error learning (where they can only covertly learn the best of what they already were able to produce - i.e. their initial range of variation), and early juveniles never perform decent song, they would never perform good song.  However, such an experiment in older juveniles might lead more noticeable learning.

(SP): A lot of other birdsong groups use zebra finches, while you guys study Bengalese Finches. Other than the fact that your entire lab is from the Ganges Delta, why do you prefer the Bengalese? 

(JC): Although this is irrelevant for the current study, Bengalese finches allow us to study both syllable sequencing and syllable structure (e.g. fundamental frequency) in the same birds.  

 (SP): What, if any, implications does your work have for dudes like me who are training to be professional MMA fighters/Gamelan singers/ forensic anthropologists? Might it be possible for me to disconnect my LMAN during practice to convince all my competitors that I was not improving, then one day reconnect it and just blow all those crummy bastards away?

Indeed our results provide hope for sandbaggers and hustlers everywhere.

Contributed by butthill
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