no tiny compasses

By what mechanism do birds migrate? How do they know where they are going? They don’t have maps. They don’t have tiny compasses. They don’t go to school. Their parents can’t tell them how. How are they born knowing how to find a place that is thousands of miles away that they have never been to?

Yellow Rumped Warbler, a favorite migratory bird (diabloaudobon.com)

For centuries, people have recorded a curious behavior in caged pet birds. At certain times of the year, they become antsy. They start flitting about in their cages, acting restless. Behavioral ecologists later dubbed this phenomenom “Zugenruhe” (zoo-gen-roo), meaning migratory restlessness in German. We came to interpret this as evidence that birds innately feel an urge to migrate at certain times of the year, a behavior likely under hormonal control, which in turn is influenced by photoperiod (how much daylight vs. night time there is in one day). But how could hormones control an organism’s navigational skills- skills that require interpretation of the cardinal directions and relative position on the earth’s surface? Simply put, hormones can’t.

The Emlen Funnel

The experiment that finally answered the question of migratory navigation was thought up and executed by a man named Dr. Steven Emlen in 1966 and is one of the most elegantly designed experiments in zoological biology. He made a simple little contraption, later named the Emlen Funnel. Imagine a funnel about the size of a large mixing bowl that has a flat bottom, atop which sits an ink pad. He lined the sides of the funnel with paper and covered the top with wire mesh. And voi-la, an Emlen Funnel. Put a bird in it, and it will get ink all over its little tooties. As it flits about, it will leave ink prints on the sides of the funnel. From this, one can tell towards what direction the bird is acclimating.

He put birds that were experiencing zugenruhe in the funnel. Tootsie prints were evenly spaced between north south east and west, meaning they were not acclimating towards any one direction. So they felt the urge to migrate, but didn’t know innately what direction to go. This is a big piece of evidence. What does it tell you?  It tells you that navigation is not innate in birds. It must be learned. How, and when, do birds learn navigational skills?! Maybe there is a secret bird school that they all go to and just manage to keep hidden from humans.

And then Emlen’s stroke of genius happened. He knew that people, sailors in particular, navigate using the stars. His university happened to have a planetarium, and so he decided to put some funnels with zugenruhe-ing birds in them under an exact replica of the night sky. And then, like magic, foot prints were overwhelmingly focused towards the south (I should mention he did this part during the fall). Once the birds caught sight of the night sky, they knew exactly where to go. They were navigating by looking at the stars. You should have just gotten the chills.

Here, Emlen got excited. He decided to start messing with the constellations (he could do that since he was in a planetarium). What he ultimately discovered was this: the birds’ navigational skills were uncompromised as long as the stars within a certain angle of the North Star were unchanged. So what does this mean? It means that they use the North Star as their primary stellar guide.

I can say without a doubt that this is my favorite biological discovery. Ever. It is beautiful and inspiring that tiny songbirds gaze at the night sky as nestlings to learn the constellations and their nightly paths across the sky. They were using the North Star to travel precisely across the hemispheres millions of years before humans clumsily developed tools like the sextant and maps to accurately travel 100 miles.

The North Star at the center of stellar movement (everett-white.com)

happy hunger games

Are you going to see the Hunger Games today? I am. I imagine since it’s opening day, it’s going to be packed. But that’s okay… if Katniss can brave a trackerjacker attack, I can brave a bunch of 12-18 year olds. I think.

In honor of the Hunger Games, we’re going to explore the fight or flight response. I’m sure you’ve heard of it and know a bit about it. On the surface, it’s basically a behavioral response that has evolved to increase our odds of survival when faced with peril. But let’s get a little grittier and talk physiology.

All your bodily processes are dependent on your nervous system. It is divided into two main systems- somatic and autonomic. You can infer their function from their names. Somatic, meaning “bodily,” is the network of nerves you control. Walking, turning your head, writing, scratching your head, whatever. It is fed information primarily from the hemispheres of the brain. Autonomic nervous system is in charge of all the processes you would consider “automatic” or involuntary like respiration, digestion, blinking, your heart beating, hormonal regulation, sweating, and getting frisky. It is controlled by your brain stem, meaning it is of rudimentary evolutionary origins.

So, since it’s science, we have to divide these systems further because two categories just aren’t enough. Your autonomic nervous system is divided into two more systems- parasympathetic and sympathetic. The parasympathetic is in charge of maintaining your body at rest, which is pretty much digestion and hormones. But your sympathetic…. that’s what you want around in a trackerjacker attack. It activates during a time of stress and tells your muscles what to do when you may not have enough time to sit and think about it. Cato will surely have speared you by the time you consciously figure out the best way to handle him.

The sympathetic system is what is in charge of the flight or fight response. At the moment you realize you’re in trouble, your sympathetic system douses your tissues with the hormone adrenaline, which allows for extremely quick and sudden muscular activity. It also increases your heart rate, breathing, pupil size, and blood vessel constriction.

I think what it inhibits is even more interesting. It temporarily shuts down digestion, tear and spit production, some hearing ability, an erection (if you are a male and have one…. awkward), and peripheral vision. While some of these reactions may surprise you, you can figure out that they function to eliminate extraneous and unessential processes so that maximal energy can be devoted to vital ones- the ones that will help you come out of the situation alive. You don’t need to be digesting that Whataburger you had for lunch at a time like this, and your sympathetic nervous system knows it.

When this response is combined with sensory input, it allows for your brain to make a rapid assessment on what to do. In some cases, you’ll run. In other’s you’ll fight back. It depends on lots of environmental and situational variables, but your sympathetic nervous system has primed and prepped your body for action one way or the other.

I know you’ve experienced this stress response before… probably in a near miss while driving. It takes a few minutes to process the adrenaline out of your bloodstream and calm down. Thousands of years ago, however, this response was more likely elicited by Thor from the tribe on the other side of the river coming after you with a club, or a bear the size of a Buick trying to eat you. I find it funny that nowadays, this very same response can be initiated by realizing you forgot to pay rent.

But this is not so in future Panem. They’re not worried about paying rent or getting in a fender bender, they’re worried about other adolescents beating their heads in with a log in the Hunger Games. Katniss and Peeta better hope they have fully functional sympathetic nervous systems, or else they’ll be like fish in a barrel.

Happy Hunger Games, and may the odds be ever in your favor!

this rocks, no bones about it

Tyrannosaurus rex fossil

At natural history museums, the star attractions are usually the dinosaur skeletons. Kids usually can’t wait to see the T-rex, brontosaurus, and stegosaurus bones. But little do they know that what they are seeing are not actually the bones of the dinosaurs. They are fossils.

Fossilization, in the simplest sense, is the preservation of what was once organic into something inorganic. Bones are the most recognizable fossilized things, but not the only and certainly not the most common. Just to name a few things that can be fossilized: shells, tracks left in the ground, pollen, imprints of animals, wood, and poo. (A fossilized piece of poo is called a coprolite.) But today, we’re just going to cover the fossilization of prehistoric animal bones, since generally people deem them the most exciting.

To be fossilized, an animal must die in just the right place at the right time. In fact, lots of things must go right. First off, it must be buried immediately or very soon after death. It must stay there for a very long time, allowing all soft tissues to degrade. Just the right type of rock must begin to cover the remains. The remains must resist the tremendous pressure of the resulting rock over millions of years. And then some jerk has to find it. What are the chances of all that happening? It’s amazing we have as many fossils as we do.

Apatosaurus Louie (rareresourse.com)

To make this process a little less abstract, let’s talk about a specific example. An Apatosaurus named Louie is taking a walk 152 million years ago when he breaks his leg while drinking from a riverbed. Louie struggles to walk but can’t, and dies from starvation a few days later. The water and the sediment suspended within it begins to cover Louie up. After a while, he is totally buried beneath the sediment. By then, the decomposition process has started. Skin, muscle, and connective tissue becomes gooey and breaks down. Water and body fluids dissipate into the surroundings. After a short while, only inorganic body parts are left- bones, teeth, etc. Now we jump into warp speed-  because the rest of the fossilization process takes millions of years.

More sedimentary rock (like the rock in the Grand Canyon) begins to form on top of Louie’s final resting place. Rock begins pressurizing his bones, and minerals and microscopic bits of rock are forced into the tiny open spaces of his bones. As time goes on and the pressure becomes greater, so does the level and detail of fossilization. The inorganic minerals that were original to Louie’s bones (like calcium) are still there, but the empty spaces are now filled with rock. Louie’s bones have been rock-ified. The podcast “Stuff You Should Know” from howstuffworks.com likens this process to filling a sponge with glue- the original minerals of Louie’s bones are still, but sort of cemented in position. So really, the fossilized skeletons you see at museums are more rock than they are bone.

Now Enter Dr. Grant. In order to be found, the rock in which Louie was preserved must have moved and shifted over the millenia in such a way that his remains are relatively close to the surface, or side of the rock. Someone has to know to look there… which is improbable and then requires a whole lot of luck. Then someone who knows what they’re doing must exhume the remains without effing up. The chances of an animal’s remains making it all the way into a natural history museum are miniscule. But those fossils that we have found and unearthed comprise the fossil record- which is all of the fossils we have found considered as a whole in the context of where they appear in the strata. The fossil record tells the chronological story of the evolution of life on earth.

Lots of evolution opponents argue that the lack of a complete fossil record is evidence against evolution. They argue that if animals evolve slowly and gradually, we should have record of all the stages in between the old and new fauna. Where’s the man-monkey, they ask? Where’s the bird-dinosaur? Where’s the fish-landanimal? “Show us the transition fossils!” they say.

Now being more familiar with the fossilization process, what would you say to them? Hopefully something along the lines of, “fossils aren’t a dime a dozen, PAL,” or “only a fraction of the species that lived were lucky enough to be fossilized, BUDDY,” or "we only are able to locate a small percentage of the fossils, FRIEND." And then, start naming the incredible transition fossils we do have.

Tiktaalik- link between fish and tetrapods. Fossil found in ice regions of Canada (wikicommons)

Archaeopteryx- link between dinos and birds. Fossil found in Germany. (wikicommons)

Ambulocetus- link between land animals and whales. Fossils found in Pakistan (wikicommons)

I mentioned the Podcast “Stuff You Should Know” from howstuffworks.com. I recommend you go to iTunes and subscribe to it right now. It’s free. Josh and Chuck, the hosts, explain all sorts of cool things from withcraft to dark matter. And they’re pretty funny. 

when two plants love each other very much

I know I’m not the only one who is sneezing with an itchy face and eyes this week. Cars are turning yellow and you literally have to windshield-wipe off the pollen in order to drive. But even though we are all covered in plant sperm, we can still appreciate the miracle of pollination with the onset of spring.

Male cones on the left, female on the right (emhsbot-zoo.wikispaces.com)

With exceptions here and there, there are no such things as “girl plants” and “boy plants.” Let’s take a pine tree for example (they’re the main culprits to blame for your car right now, FYI): a single pine tree has both male and female structures. The pinecone is the female structure, and the little yellow dangly things are the male structures. The yellow dangly things release the pollen, and the cones receive. And lots of plants have what you could consider an allergy to their own pollen so that they cannot self-fertilize. This way, pine trees swap pollen with each other to increase genetic diversity and have healthier baby pine trees. In this case, wind is the main vector by which trees swap pollen.

Insects are also vectors for pollination. A bee, for example, might land on a daisy. As it sticks its face down into the flower to lick out nectar, pollen gets stuck on its little legs and underbelly. Then it flies to the next flower and sticks its face into it, all the while pollen from the previous flower getting all over this one. Without even realizing it, the bee has brought pollen from one flower to another. Clueless little flower-sex-enabling insect.

Looks like a bee! (fs.fed.us)

Oh but don’t worry, there are even more clueless insects than these daisy-pollinating bees. Orchids, an especially dazzling group of flowering plants, have evolved some unique pollination adaptations that take advantage of their insect pollinators. Some of them, to put it simply, look like an insect in order to trick a member of that insect species to try and mate with it. The unsuspecting bug will enthusiastically rub its little insect self all up ON that orchid, becoming covered in pollen. Once the bee realizes that it’s trying to have sex with a flower and it checks to make sure its friends didn’t see, it flies off to the next orchid and does it all over again. What’s a bug gotta do for some same-species lovin around here?!

Looks like a wasp (whyevolutionistrue.wordpress.com)

It’s important to remember that this mechanism is the result of evolution, and not cognitive trickery on the part of the orchid (it’s a plant). Nonetheless, the resulting flowers are astounding.

SUCKER! (eyesseetheworldspinninground.blogspot)

Happy spring break, all.

shake ya orange-colored rectrice

Last night, my significant other took me to my first real-live concert in Atlanta. We had floor tickets, meaning we were right up close to the stage (I could see Thom Yorke’s eyeballs). My first real, indoor concert was a success- they even played my favorite song. I was on a Radiohead high as we left.

Once we got back to the car, I began to notice that everything sounded sort of muted. Kind of like when you have a cold and sounds are muffled and dull. After expressing concern that I might be having a stroke or spontaneously going deaf, he explained that it is normal after concerts to experience this. Jeez, the music didn’t sound that loud to me. Hearing is more sensitive than we think.

Notice the bright yellow tail tip (commongroundsonline.com)

A group of 6 birds let me know this morning that my hearing was back. As I left my apartment for work, I heard the soft wheezy calls of Cedar Waxwings perched way up high in a tree. These birds used to provide me cheap amusement during my ornithology labs when I was a senior. There were a bunch of big burly dudes in the class who could never hear the Cedar Waxwings calling. The TA would point out the wheezy sound, and everyone would turn their heads in the direction of the birds to get a better listen. The guys dressed in camo, turning their heads furiously (but not so fast as to sling out their dip) would try hear what everyone else did. But they couldn’t- years of hunting with loud guns had destroyed their ability to detect sounds in such a high frequency range. The poor guys will never be able to enjoy the Waxwing’s call.

I’ve mentioned Cedar Waxwings before- I think they are the bees knees. They are very pretty, and the crests on their heads makes them all look like little bird royalty. They are called Waxwings due to waxy-looking red structures that decorate the tip of their wings. Another pretty attribute are the tips of their rectrices (fancy word for tail feathers)- which were usually a bright yellow. However, a curious thing started to happen in the mid 1960’s. Some Cedar Waxwings’ rectrices turned orange.

When birds have red, yellow, or orange colors, it’s due to pigments called carotenoids. The tricky part about carotenoids is that they cannot be manufactured by the body. Vertebrates simply do not have the physiological machinery to make them. So then, how do birds show colors based on pigments their bodies cannot make? Answer: they eat them.

Birds acquire carotenoids via their diet, usually from brightly colored berries that contain carotenoids. When people started looking in to the orange-tip phenomonen, they found that it coincided with the introduction of a new species of honeysuckle whose berries contained a red carotenoid pigment called rhodoxanthin (road-oh-zan-thin). Come to find out, the orange tips were a result of the consumption of these newfangled red berries. New red carotenoids and the standard yellow carotenoids make orange. Pretty cool, eh?

I had never actually seen an orange-tipped Waxwing, until recently. And I didn’t even see the bird. I found three feathers out in the woods with strikingly beautiful yellow-orange tips. It was one of the most gratifying discoveries I’ve ever made. Technically, it is illegal to be in possession of any migratory bird’s feathers due to the Migratory Bird Treaty Act. So I definitely did not take them. And this is definitely not a picture of them. And I definitely don’t sleep with them by my bed.

This is a cool paper that breaks down the tail tip coloration story:

Evidence supporting a dietary basis for orange-tipped rectrices in the Cedar Waxwing by Mulvihill, Pakres, Leberman, and Wood. Journal of Field Ornithology, Vol. 63, No. 2, Spring, 1992.