Birds of a feather

The diversity you find among birds is really remarkable.

There are differences in bill shape, from the weird angled beaks of flamingos, to the longer-on-the-bottom fish skewers of skimmers, to the upswept needle of the avocet, to the absurd (and aptly-named) spoonbills and shoebills, to the pelicans -- about whom my dad taught me a limerick when I was little:

A wonderful bird is the pelican.
His bill can hold more than his bellican.
He can stash in his beak
All his food for the week,
But I really don't see how the hellican.

Yeah, it's kind of obvious where I got my sense of humor from.

Of course, it doesn't end there. The impossibly long toes of the South American jacanas (called "lilytrotters" because they can walk on the floating leaves of waterlilies).  The phenomenal wingspan of the albatross.  The insane plumage of the birds-of-paradise.

And the colors.  Man, the colors!  Even in my decidedly non-tropical home we have some pretty amazing birds.  The first time I saw an Indigo Bunting, I was certain that one of my sons had put a blue plastic bird on the bird feeder just to rattle my chain.  There couldn't be a real bird that was that fluorescent shade of cobalt.

Then... it moved.

But nothing prepared me for the colors I saw on my visits to Ecuador, especially amongst the birds of the tanager family.  There are hundreds of species of tanagers in that tiny little country, and because they often travel in mixed foraging flocks, you can sometimes see twenty or thirty different species in the same tree.  These include the Green-headed Tanager:

[Image licensed under the Creative Commons Lars Falkdalen Lindahl (User:Njaelkies Lea), Green-headed Tanager Ubatuba, CC BY-SA 3.0]

The Black-capped Tanager:

[Image licensed under the Creative Commons Joseph C Boone, Black-capped Tanager JCB, CC BY-SA 4.0]

And the Flame-faced Tanager:

[Image licensed under the Creative Commons Eleanor Briccetti, Flame-faced Tanager (4851596008), CC BY-SA 2.0]

Being a biologist, of course the question of how these birds evolved such extravagant colors is bound to come up, and my assumption was always that it was sexual selection -- the females choosing the most brightly-colored males as mates (in this group, as with many bird species, the males are usually vividly decked out and the females are drab-colored). If over time, the showiest males are the most likely to get lucky, then you get sexual dimorphism -- the evolution of different outward appearances between males and females.  (This isn't always so, by the way.  Most species of sparrows, for example, have little sexual dimorphism, and even experienced birders can't tell a male from a female sparrow by looking.)  More puzzling still is the general trend that tropical birds are more brilliantly-colored than bird species in higher latitudes -- a trend that is yet to be convincingly explained.

The reason this comes up today is two papers that came out last week.  The first, that appeared in Science Advances, looks at one of the most amazing things about their evolutionary history -- they were the only branch of the dinosaur clade that survived the cataclysmic mass extinction at the end of the Cretaceous Period.  What allowed birds to make it through the bottleneck that killed all of their near relatives -- and not only survive, but thrive and rediversify?

The evidence is that the extinction event selected for two things; small body size, and a shift toward young being altricial -- born relatively helpless and undeveloped, and therefore requiring more parental care.  Some lineages of birds would eventually increase in body size again, but they never again would reach the colossal proportions that their cousins did during the Jurassic and Cretaceous Periods.

"We have typically not looked at the change in DNA composition and model across the tree of life as a change that something interesting has happened at a particular point of time and place," said Stephen Smith, of the University of Michigan, who co-authored the study.  "This study illustrates that we have probably been missing something...  We found that adult body size and patterns of pre-hatching development are two important features of bird biology we can link to the genetic changes we’re detecting.  One of the most significant challenges in evolutionary biology and ornithology is teasing out the relationships between major bird groups — it’s difficult to determine the structure of the tree of life for living birds."

The study not only elucidated relationships between extant groups of birds, it allowed the researchers to pinpoint when groups diverged from each other, and therefore what innovations were likely to be connected with events occurring on the Earth at the time.

The second study, which appeared in Nature Ecology & Evolution, looked at the question I began with -- the impossibly bright colors that are characteristic of so many bird species.  Colors in birds arise two ways -- pigments (chemicals which absorb some frequencies of light and reflect others) and structural color (due to feathers creating a combination of refraction and interference; this is also known as iridescence).  Most pigmented color in birds is relatively drab -- blacks, grays, and various shades of brown -- the flashing blues, greens, and purples you see in groups like tanagers, hummingbirds, and sunbirds are almost entirely due to iridescence.

The researchers went through images of as many of the 9,409 species of birds currently in existence, along with the current best iteration of the family tree of birds, to try and figure out where along the way iridescence evolved, and how it spread so widely among this class of animals.  

And what they found was that 415 distantly-related branches of the tree have iridescent feathers, and the common ancestor of all modern birds -- something like eighty million years ago -- was very likely iridescent.

"I was very excited to learn that the ancestral state of all birds is iridescence," said Chad Eliason, of the Field Museum in Chicago, who was the paper's lead author.  "We've found fossil evidence of iridescent birds and other feathered dinosaurs before, by examining fossil feathers and the preserved pigment-producing structures in those feathers.  So we know that iridescent feathers existed back in the Cretaceous -- those fossils help support the idea from our model that the ancestor of all modern birds was iridescent too."

There are still a lot of questions left unanswered, however.  "We still don't know why iridescence evolved in the first place," Eliason said.  "Iridescent feathers can be used by birds to attract mates, but iridescence is related to other aspects of birds' lives too.  For instance, tree swallows change color when the humidity changes, so iridescence could be related to the environment, or it might be related to another physical property of feathers, like water resistance.  But knowing more about how there came to be so many iridescent birds in the tropics might help us understand why iridescence evolved."

Which is extremely cool.  Something to think about next time you see one of those brilliant little flying jewels flit by.  The stunning colors we appreciate every day on our bird feeders and in the wild have a very long history -- going back to a trait that evolved something like eighty million years ago.

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Song of the Rifleman

As an avid birdwatcher, I've learned many of the vocalizations of our local species.  Some, especially the migratory species we only hear from May to September, I have to relearn every year, but a few of them are so distinct that my ears perk up whenever I hear them.  One of my favorites is the whirling, ethereal song of the Veery (Catharus fuscescens):

Another lovely one, often heard in the same sorts of deep-woods habitats as the Veery, is the Wood Thrush (Hylocichla mustelina):

By far the strangest bird songs I've ever heard, though, we came across when we visited the lowlands of eastern Ecuador about twenty years ago.  There were two we heard but never saw -- first, the aptly-named Screaming Piha (Lipaugus vociferans), which can be heard for miles:

And second, the Great Potoo (Nyctibius grandis), which is cryptically-colored and nocturnal, so they're almost never seen.  But when they sing at night... holy crap.  Imagine being out in the jungle, alone, at night, and hearing this:

It's no wonder the locals thought there were monsters out there.

Bird songs serve two main purposes.  They're territorial defense signals and mate attractants.  (Which led a former student of mine to say, in some astonishment, "So birds only sing when they're mad or horny?")  Songs are usually only done by males, and mostly during the breeding season.  Calls, on the other hand, are done by both males and females, at any time of the year, and can mean a variety of things from "there's food over here" to "watch out for the cat" to "hey, howsyamommaandem?"  (The latter mostly from birds in the southeastern United States.)  Those of you in the eastern half of North America certainly already have heard the difference; our local Black-capped Chickadee (Poecile atricapillus) has a call, the familiar "chicka-dee-dee-dee-dee" that gives the species its name, and a song -- a two-note whistle with the second note a whole step below the first.  Listening to them, you'd never guess it was the same bird.

There's an interesting distinction in how animals vocalize.  Some vocalizations seem to be innate and hard-wired; the barking of dogs, for example, doesn't need to be learned.  A great many bird species, however, including songbirds and parrots, learn vocalizations, and deprived of examples to learn from, never sing.  (This includes the amazing mimicry of birds like the Australian Superb Lyrebird (Menura novaehollandiae), which can learn to imitate not only birdsongs but a huge variety of other sounds as well):

The topic comes up because of a study that came out this week in the journal Communications Biology about the Rifleman (Acanthisitta chloris), a tiny species from New Zealand that is one of only two surviving species in the family Acanthisittidae, the New Zealand wrens, which are only distantly related to the more familiar and widespread true wrens.  (If you're curious, its odd common name comes from the cheerful colors of the plumage, which someone decided looked like a military uniform:

[Image licensed under the Creative Commons digitaltrails, Lake Sylvan - Rifleman (5626163357) (cropped), CC BY-SA 2.0]

The Rifleman is not a songbird, and (if the preceding distinction holds) should be unable to learn vocalizations; any sounds it makes should be instinctive and fixed, like the clucking of a chicken.  But the study found that there were variations in the vocalizations of different individuals, and those variations were independent of how closely related they were; what mattered was how nearby they lived to each other, implying that the alterations in sound were learned, not innate. 

"The vocal behavior that we were unravelling in this study is very similar to what is known as vocal accommodation in human linguistics," said Ines Moran, of the University of Auckland, who led the research.  "It's similar to our ability to adjust our ways of speaking in different social, dialectal, or hierarchical settings -- modulating our voices to better fit in certain social groups."

So bird vocalizations may not be as simple as we'd thought.  Like most things, I suppose.  It brings up the silly distinction that I heard over and over again from students, that there's a split between "human" and "animal."  We're clearly animals; and, conversely, what we call "animals" share a great deal more with us than we often realize.  We have a lot to learn from the other species we whom we cohabit the planet.  It's nice that we're beginning to pay more attention.

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Flocking together

One of the most mesmerizing sights in nature is the collective motion of large groups of animals.

I remember watching films by Jacques Cousteau as a kid, and being fascinated by his underwater footage of schools of fish swimming along and then turning as one, the light flickering from their silvery sides as if they were each reflective scales on a giant single organism.  Murmurations of starlings barely even look real; the flocks swirl and flow like some kind of weird, airborne fluid.  But the most astonishing example of collective motion I've ever seen was when Carol and I visited Bosque del Apache Wildlife Refuge, in central New Mexico, a few years ago, during the migration of snow geese through the region.

"Get there early," we were told.  "At least a half-hour before sunrise.  You'll be glad you did."

We arrived just as the light was growing in the eastern sky.  The wetland was full of tens of thousands of snow geese, all moving around in a relaxed sort of fashion, calling softly to each other.  The brightness in the sky grew, and then -- without any warning at all...

... BOOM.

They all exploded into the air, seemingly simultaneously.  We have wondered many times since what the signal was; there was nothing we could discern, no handful of birds that launched first, no change in the vocalizations that a human would interpret as, "Now!"  One moment everything was calm; the next, the air was a hurricane of flapping wings.  They whirled around, circling higher and higher, and within ten minutes they were all gone, coursing through the sky toward their next destination.

[Image licensed under the Creative Commons CrunchySkies, Snow goose migration at Squaw Creek National Wildlife Refuge, Feb 2013, 25, CC BY-SA 3.0]

How animals manage such feats, moving as a unit without colliding or leaving members behind -- and seemingly without any central coordination -- has long fascinated zoologists.  Way back in 1987, computer simulation expert Craig Reynolds showed (using software called "Boids") that with only a handful of simple rules -- stay within so many wing-lengths of your nearest neighbors but not close enough to touch, match the speed of your neighbors within ten percent either way, steer toward the average heading of your nearest neighbors, give other members a chance to be in any given position in the group -- he was able to create simulated flocking behavior that looked absolutely convincing.  

Last week, a paper out of the Max Planck Gesellschaft showed there's another factor that's important in modeling collective motion, and this has to do with the fact that flying or swimming animals have a rhythm.  Look, for example, at a single fish swimming in an aquarium; its motion forward isn't like a car moving at a steady speed down a highway, but an oscillating swim-glide-swim-glide, giving it a pattern a little like a Slinky moving down a staircase.

Biologist Guy Amichay, who led the research, found that this gives schools of fish a pulse; he compares it to the way we alternate moving our legs while walking.  "Fish are coordinating the timing of their movements with that of their neighbor, and vice versa," Amichay said.  "This two-way rhythmic coupling is an important, but overlooked, force that binds animals in motion.  There's more rhythm to animal movement than you might expect.  In the real world most fish don't swim at fixed speeds, they oscillate."

The key in simulating this behavior is that unlike the factors that Reynolds identified, getting the oscillating movement right depends on neighboring fish doing the opposite of what their nearest neighbors are doing.  The swim-glide pattern in one fish triggers a glide-swim pattern in its friends; put another way, each swim pulse creates a delay in the swim pulse of the school members around it.  

"It's fascinating to see that reciprocity is driving this turn-taking behavior in swimming fish, because it's not always the case in biological oscillators," said study co-author Máté Nagy.  "Fireflies, for example, will synchronize even in one-way interactions.  But for humans, reciprocity comes into play in almost anything we do in pairs, be it dance, or sport, or conversation,"

"We used to think that in a busy group, a fish could be influenced by any other member that it can see," said co-author Iain Couzin. "Now, we see that the most salient bonds could be between partners that choose to rhythmically synchronize."

So zoologists have taken another step toward comprehending one of the most fascinating phenomena in nature; the ability of animals to move together.  Something to think about next time you see a school of fish or a flock of birds in flight.  Getting it right requires rapid and sophisticated coordination we are only now beginning to understand.

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Dream songs

Last night I dreamed that our local mall had been converted into a giant used book store.  (Something I would entirely approve of.)  We were going to to go shopping ("we" being my wife, me, and our younger son, who lives in Houston but was apparently up for a visit) but we realized that a bunch of other family members were unexpectedly going to descend upon us, and for some reason we knew they were going to walk into our house without knocking, which our dogs would not appreciate, so we had to get home fast.  But while trying to get out of the mall we were hindered by a bunch of science-fiction cosplayers wearing silver body paint.

After that, it got kind of weird.

Dreams are a very peculiar thing, but they (and the REM sleep stage during which they occur) are ubiquitous in the brainier species of animals.  In fact, as I'm writing this, my puppy Jethro is curled up in his bed by my desk dreaming about something, because his paws are twitching and every once in a while he makes a very cute little "oof" noise.  But what would a puppy dream about?  Presumably the things that make up his waking life -- playing, chasing squirrels, swimming in our pond, eating his dinner.

You have to wonder if sometimes dogs, like humans, have weird dreams, and what they might make of them.

The function of dreaming is unknown, but what's certain is that it's necessary.  Suppress REM and dreaming, and the results are hallucinations and psychosis.  Aficionados of Star Trek: The Next Generation will no doubt remember the chilling scene in the episode "Night Terrors," where something is preventing the crew from experiencing REM sleep, and Dr. Crusher is in the makeshift morgue where the victims of a massacre are being examined -- and when she turns around, all the dead bodies are sitting up, still shrouded in their sheets.  She closes her eyes -- exhibiting far more bravery than I would have -- and says, "This is not real," and when she opens them, they're all lying back down again.

*shudder*

In any case, what brings up this topic today is far cheerier; a fascinating piece of research out of the University of Buenos Aires that looked at dreams in an animal we usually don't associate with them -- birds.  A team led by Gabriel Mindlin looked at a species of bird called the Great Kiskadee (Pitangus sulphuratus), a brightly-colored and vocal flycatcher found in much of Central and South America.  

Mindlin is one of the foremost experts in the physiology of bird song.  Birds have a unique apparatus called the syrinx that allows them to make some of the most complex vocalizations of any group of animals; not only can some (such as many wrens and thrushes) produce two or more tones at the same time, birds like parrots, mynahs, lyrebirds, and starlings are brilliant mimics and can imitate a variety of other sounds, including human speech.  (A lyrebird in a park in Australia learned to convincingly imitate a chainsaw, a car alarm, various cellphone ringtones, and a camera shutter.)

What Mindlin and his team did was to implant electrodes in the obliquus ventralis muscle, the main muscle birds use to control pitch and volume in vocalization, and also outfit some Great Kiskadees with devices to monitor their brain waves.  When the birds went into REM sleep, the researchers found that the OV muscle was contracting in exactly the way it does when the birds vocalize while awake.

The birds were singing silently in their sleep!

Singing in birds generally serves two purposes; mate attraction and territorial defense.  (As one of my AP Biology students put it, "they sing when they're mad or horny.")  It's more complicated than that -- science generally is -- but as a broad-brush explanation, it'll do.  Many species have different songs and calls for different purposes, each associated with a specific pattern of contractions and relaxation of the muscles in the syrinx.  Mindlin and his team used software capable of taking the muscle movements the electrodes detected and decoding them, determining what song the bird would have been producing if it was awake.  What they found was that the song their test subjects were dream-singing was one associated with marking out territories. 

"I felt great empathy imagining that solitary bird recreating a territorial dispute in its dream," Mindlin said.  "We have more in common with other species that we usually recognize."

So birds dream, and the content of their dreams is apparently -- just like Jethro -- taken from their own umwelt, the slice of sensory experience they engage with while they're awake.  (I wrote in more detail about the umwelt a while back, if you're curious.)  

On the other hand, how this accounts for my dream of silver-body-painted cosplayers in a mall filled with old books, I have no idea.

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The honey hunters

One of the things I learned from 32 years of teaching biology is that many non-human animals are way smarter than we give them credit for -- and its corollary, which is that we humans are not as far separated from the rest of the natural world as many of us would like to think.

A charming piece of research in Science this week illustrates this point brilliantly.  It's about a species of African bird, the Greater Honeyguide (its scientific name, which I swear I'm not making up, is Indicator indicator).  It's found in open woodland in most of sub-Saharan Africa, and has a very specialized diet -- it lives on bee eggs, larvae, and wax (it's one of the few known animals that can digest wax).

Illustration of a Greater Honeyguide by Nicolas Huet (1838) [Image is in the Public Domain]

Because of its diet, local residents have developed a mutualistic relationship with honeyguides, a relationship that is what gives the birds their common name.  People living in the region listen for the bird's call and then follow it to find the bees' nests it was attracted to.  The people tear open the nests and take the honey -- and the bird gets the larvae and the wax.  Many cultures that live in the honeyguides' range have developed specific calls to attract the birds when they're ready to go on a honey hunt.

The study, led by ecologist Claire Spottiswoode of the University of Cambridge, looked at the fact that honeyguides seem to learn the specific calls used by the people they live near.  Initially, it was uncertain if the people had figured out what the birds responded to, or if the reverse was true and the birds had learned what noises the people made.  So she and her team decided to test it; they used recordings of individuals from two cultures that are known to use honeyguides, the Hadza of Tanzania and the Yao of Malawi and Mozambique.  The Hadza employ a complex series of whistles to summon their helpers, while the Yao make a "brrr-huh" sound.

Both signals work just fine, but only in particular regions.  When a recording of the Hadza signal is played in Malawi, or a recording of the Yao signal is played in Tanzania, the birds don't respond.  The birds have evidently learned to recognize the specific calls of their partners in the region where they live -- and don't "speak the language" used elsewhere.

Spottiswoode's team also found there are two places where the symbiotic relationship is falling apart.  In more urban areas, where commercial sugar is widely available, there are fewer people engaged in honey hunting, so the birds have decided they're better off working as free agents.  Even more interesting, in some areas in Mozambique, the Yao discovered that if they destroy the wax and the rest of the hive, the honeyguides will stay hungry and look for other nests.  But... the birds are learning that their human partners are stiffing them, and they're becoming less likely to respond when called, so the human honey hunters are having less overall success.

So even birds can recognize when they're getting a raw deal, and put a stop to it.

The more we find out about the other life forms with which we share the planet, the more commonality we find.  Everything in the natural world exists on a continuum, from our physiology and our genetics to characteristics many thought of as solely human traits, like emotion, empathy, and intelligence.

So be careful when you throw around terms like "bird-brain" -- they're not as far off from us as you might like to believe.

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Birds down under

I've been an avid birdwatcher for many years, and have been fortunate enough to travel to some amazingly cool places in search of avifauna.  Besides exploring my own country, I've been to Canada (several times), Belize (twice), Ecuador (twice), Iceland (twice), England (twice), Scotland, Sweden, Finland, Denmark, Russia, Spain, Portugal, and Malaysia.

One place I've never been, though, is Australia, which is a shame because it's got some incredible animals.  And despite a pretty well-deserved reputation for having far more than their fair share of wildlife that's actively trying to kill you, most tourists come back from trips to Australia alive and with all their limbs still attached in the right places.

The main reason for Australia's unique ecosystems is that it's been isolated for a very long time.  During the breakup of Pangaea, the northern part (Laurasia, made up of what is now Europe, North America, and most of Asia) separated from the southern part (Gondwanaland, made up of what is now Africa, South America, Antarctica, Australia, and India), something on the order of 180 million years ago.  The other pieces gradually pulled apart as rifting occured, but Australia remained attached to Antarctica until around thirty million years ago.  At that point, the whole thing had a fairly temperate climate, but when the Tasman Gateway opened up during the Oligocene Period, it allowed the formation of the Antarctic Circumpolar Current, isolating and cooling Antarctica and resulting in the extinction of nearly all of its native species.  Australia, now separate, began to drift northward, gradually warming as it went, and carrying with it a completely unique suite of animals and plants.

The reason all this comes up is a sharp-eyed Australian loyal reader of Skeptophilia, who sent me a link to a news story about a recent discovery by a dedicated amateur fossil hunter and birdwatcher, Melissa Lowery, who was looking for fossils on the Bass Coast of Victoria and stumbled upon something extraordinary -- some 125 million year old bird footprints.

Lowery's bird footprints [Image by photographer Rob French, Museums Victoria]

At that point, the separation of Australia and Antarctica was some 65 million years in the future, the sauropod dinosaurs were still the dominant animal group, and Victoria itself was somewhere near the South Pole.  Lowery's find led to a full-scale scientific investigation of the area, and uncovered a great many more bird tracks, including some with ten-centimeter-long toes.  Also in the area were the footprints of dozens of kinds of non-avian dinosaurs.

"Most of the bird tracks and body fossils dating back to the Early Cretaceous are from the Northern Hemisphere, particularly from Asia," said Anthony Martin, of Emory University, who led the study.  "Our discovery shows that there were many birds, and a variety of them, near the South Pole about 125 million years ago."

Of course, being a birdwatcher, I'm intensely curious as to what these birds looked like, but there's only so much you can tell from a footprint, or even fossilized bones.  It's simultaneously intriguing and frustrating to think about the fact that these animals -- and all the other animals and plants that lived alongside them -- had every bit of the diversity, all the curious and wonderful and beautiful adaptations and behaviors, that our modern wildlife does.

Imagine what it would be like to transport yourself back to Australia in the early Cretaceous, and witness all of that with your own eyes and ears.  (With, of course, a guarantee of coming back alive and with all your limbs still attached in the right places.  Back then, Australia was a rougher place than it is now.)

So thanks to the reader who sent me the link -- it's renewed my desire to visit Australia.  If I can't see the amazing birds they had 125 million years ago, at least I can have a look through my binoculars at some of the ones they have today.

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Pink, pink, gold

When I was in Ecuador in 2019, I was blown away by its natural beauty.  The cloud forests of the mid-altitude Andes are, far and away, the most beautiful place I've ever been, and I've been lucky enough to see a lot of beautiful places.  Combine that with the lovely climate and the friendliness of the people, and it puts the highlands of Ecuador on the very short list of places I'd happily move to permanently.

What brought me there were the birds.  It's a tiny country, but is home to 1,656 species of birds -- about one-sixth of the ten-thousand-odd species found worldwide.  Most strikingly, it has 132 different species of hummingbirds.  Where I live, in upstate New York, we have only one -- the Ruby-throated Hummingbird (Archilochus colubris) -- but there, they have an incredible diversity within that one group.  Because each species is dependent on particular flowers for their food source, some of them have extremely restricted ranges, often narrow bands of terrain at exactly the right climate and altitude to support the growth of that specific plant.  You go a few hundred meters up or downhill, and you've moved out of the range where that species lives -- and into the range of an entirely different one.

The most striking thing about the hummingbirds is their iridescence.  My favorite one, and in the top five coolest birds I've ever seen, is the Violet-tailed Sylph (Aglaiocercus coelestis):

[Image licensed under the Creative Commons Andy Morffew from Itchen Abbas, Hampshire, UK, Violet-tailed Sylph (33882323008), CC BY 2.0]

What's most fascinating about birds like this one is that the feathers' stunning colors aren't only due to pigments.  A pigment is a chemical that appears colored to our eyes because its molecular structure allows it to absorb some frequencies of light and reflect others; the chlorophyll in plants, for example, looks green because it preferentially absorbs light in the red and blue-violet regions of the spectrum, and reflects the green light back to our eyes.  Hummingbirds have some true pigments, but a lot of their most striking colors are produced by interference -- on close analysis, you find that the fibers of the feathers are actually transparent, but when light strikes them they act a bit like a prism, breaking up white light into its constituent colors.  Because of the spacing of the fibers, some of those wavelengths interfere destructively (the wavelengths cancel each other out) and some interfere constructively (they superpose and are reinforced).  The spacing of the fibers determines what color the feathers appear to be.  This is why if you look at the electric blue/purple tail of the Violet-tailed Sylph from the side, it looks jet black -- your eyes are at the wrong angle to see the refracted and reflected light.  Look at it face-on, and suddenly the iridescent colors shine out.

So the overall color of the bird comes from an interplay between whatever true pigments it has in its feathers, and the kind of interference you get from the spacing of the transparent fibers.  This is why when you recombine these features through hybridization, you can get interesting and unexpected results -- as some scientists from Chicago's Field Museum found out recently.

Working in Peru's Cordillera Azul National Park, on the eastern slopes of the Andes, ornithologist John Bates discovered what he'd thought was a new species in the genus Heliodoxa, one with a glittering gold throat.  He was in for a shock, though, when the team found out through genetic analysis that it was a hybrid of two different Heliodoxa species -- H. branickii and H. gularis -- both of which have bright pink throats.

"It's a little like cooking: if you mix salt and water, you kind of know what you're gonna get, but mixing two complex recipes together might give more unpredictable results," said Chad Eliason, who co-authored the study.  "This hybrid is a mix of two complex recipes for a feather from its two parent species...  There's more than one way to make magenta with iridescence.  The parent species each have their own way of making magenta, which is, I think, why you can have this nonlinear or surprising outcome when you mix together those two recipes for producing a feather color."

The gold-throated bird apparently isn't a one-off, as more in-depth study found that it didn't have an even split of genes from H. branickii and H. gularis.  It seems like one of its ancestors was a true half-and-half hybrid, but that hybrid bird then "back-crossed" to H. branickii at least once, leaving it with more H. branickii genes.  All of which once again calls into question our standard model of species being little cubbyholes with impermeable walls.  The textbook definition of species -- "a morphologically-distinct population which can interbreed and produce fertile offspring" -- is unquestionably the most flimsy definition in all of biology, and admits of hundreds of exceptions (either morphologically-identical individuals which cannot interbreed, or morphologically-distinct ones that hybridize easily, like the Heliodoxa hummingbirds just discovered in Peru).

In any case, the discovery of this hybrid is fascinating.  You have to wonder how many more of them there are out there.  The fact that its discovery ties together the physics of light, genetics, and evolution is kind of amazing.  Just further emphasizes that if you're interested in science, you will never, ever be bored.

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New jaws in an old bird

One difficulty in building evolutionary trees of life from fossil evidence is the fact that "simpler" doesn't necessarily mean "older."

It's an understandable enough mistake.  Taken as a whole, from life's first appearance some 3.7 billion years ago until today, there has been an overall increase in complexity.  The problem occurs when you try to apply that overarching trend to individual lineages -- and find that over time, some species have actually become less complex.

A good example is Subphylum Tunicata, less formally known as tunicates or sea squirts.  At a glance, tunicates look a little like sponges (to which they are only very distantly related); simple, sessile filter feeders.  It was only when biologists discovered their larvae that they realized the truth.  Tunicates are much more closely related to vertebrates than they are to simple invertebrates like the sponges and corals they superficially resemble.  The larvae look a bit like tadpoles, but as they develop the sequentially lose structures like the notochord (the flexible rod that supports the dorsal nerve cord; in us, it ends up becoming the discs between our vertebral bones), most of the muscle blocks, and in fact, just about all their internal organs except the ones involved in processing food and reproducing.

As evolutionary biologist Richard Dawkins put it, evolution is "the law of whatever works."  It doesn't always lead to becoming bigger, stronger, faster, and smarter.  If being small, weak, slow, and dumb works well enough to allow a species to have more surviving offspring -- well, they'll do just fine.

The reason this topic comes up is because of a paper in Nature about a re-analysis of a bird fossil found in a Belgian quarry two decades ago.  The comprehensive study found that one of the bones had been misidentified as a shoulder bone, but was actually the pterygoid bone -- part of the bony palate.  And that bone showed that the species it came from, a heron-sized toothed bird Janavis finalidens, had been misplaced on the avian family tree.

And that single rearrangement might restructure the entire genealogy of birds.

Artist's reconstruction of Janavis finalidens [Image courtesy of artist Philip Krzeminski]

There are two big groups of modern birds; neognaths, which have jaws with free plates allowing the bills to move independently of the skull, and paleognaths, whose jaw bones are fused to the skull.  The paleognaths -- including emus, cassowaries, tinamous, and kiwis -- were thought to be "primitive" in the sense of "more like the ancestral species."  (If you know some Greek, you might have figured this out from the names; paleognath means "old jaw" and neognath means "new jaw.")

But the new analysis of Janavis, a species dating to 67 million years ago -- right before the Chicxulub Meteorite hit and ended the Cretaceous Period and the reign of the dinosaurs -- shows that it was a neognath, at a time prior to the split between the two groups.

Meaning the neognaths might actually have the older body plan.

If this is true -- if the paleognaths evolved from the neognaths, not the other way around -- the puzzle is why.  The flexible beaks of neognaths seems to be better tools than the fused jaws of the paleognaths.  This, though, brings us back to our original point, which is that evolution doesn't necessarily drive species toward complexity.  It also highlights the fact that if a structure works well enough not to provide an actual survival or reproductive disadvantage, it won't be actively selected against.  A good example, all too familiar to the males in the audience, is the structure of the male reproductive organs -- with the urethra passing through the prostate gland (leading to unfortunate results for many of us as we age), and the testicles outside the abdominal cavity, right at the perfect height to sustain an impact from a knee, the corner of a table, or the head of a large and enthusiastic dog.  (If this latter example seems oddly specific, I can assure you there's a galumphing galoot of a pit bull currently asleep on my couch who is the reason it came to mind.)

Anyhow, it looks like we might have to rethink the whole "paleognath" and "neognath" thing.  Makes you wonder what else on the family tree of life might need some jiggering.  

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Jurassic rainbow

Regular readers of Skeptophilia might recall that about a year ago, paleontologists announced the discovery of a bird fossil from northeastern China that had a long, pennant-like tail -- and that from the extraordinary state of preservation, they were able to determine that the outer tail feathers had been gray, and the inner ones jet black.

Determining feather, hair, and skin color of prehistoric animals is remarkably tricky; the pigments in those structures break down rapidly when the animal's body decomposes, and the structures themselves are fragile and rarely fossilize.  The result is that when artists do reconstructions of what these animals may have looked like, they base those features on analogies to modern animals.  This is why in old books on dinosaurs, they were always pictured as having greenish or brownish scaly skin, like the lizards they were thought to resemble, even though dinosaurs are way more closely related to modern birds than they are to modern lizards.  (To be fair, even the paleontologists didn't know that until fairly recently, so the artists were doing their best with what was known at the time.)

But it does mean that if we were to get in the TARDIS and go back to the Mesozoic Era, we'd be in for a lot of surprises about what the wildlife looked like back then.  Take, for example, the late Jurassic Period fossil found by a farmer in China that contained the nearly-complete skeleton of a birdlike dinosaur.  Here's the fossil itself:

What's remarkable about this fossil is that the feathers were so well-preserved that paleontologists were able to get a close look at the melanocytes -- the pigment-containing cells -- and from the arrangement and layering of those cells, they determined that the dinosaur's head feathers were arrayed like a rainbow, similar to modern hummingbirds, sunbirds, and trogons.

So here's the current reconstruction of what this species looked like:

[Reconstruction by artist Velizar Simeonovski, of The Field Museum]

Kind of different from the drab-colored overgrown iguanas from Land of the Lost, isn't it?

The species, christened Caihong juji from the Mandarin words meaning "big rainbow crest," adds another ornate member to the late Jurassic and early Cretaceous fauna of what is now northern China.  And keep in mind that we only know about the ones that left behind good fossils -- probably less than one percent of the total species around at the time.  As wonderful as it is, our knowledge of the biodiversity of prehistory is analogous to a future zoologist trying to reconstruct our modern ecosystems from the remains of a sparrow, a cat, a raccoon, a deer, a grass snake, and a handful of leaves from random plants.

I think my comment about being "in for a lot of surprises" if we went back then is a significant understatement.

Even so, this is a pretty amazing achievement.  Astonishing that we can figure out what Caihong juji looked like from some impressions in a rock.  And it gives us a fresh look at a long-lost world -- but one that was undoubtedly as rainbow-hued and iridescent as our own.

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Big bird

If last week's post about the Demon Ducks of Australia wasn't sufficient to scare you into stopping your project to build a working time machine so you can study prehistoric life first-hand, take a look at a different recent fossil discovery -- this one of a bird with a six-meter wingspan...

... and teeth.

Well, pseudoteeth, says the Wikipedia article on pelagornithids, because they don't have the same structure as true teeth and are actually outgrowths of the premaxillary and mandibular bones.  But that would have been little consolation to their prey:

This rather horrifying discovery, which I found out about thanks to a loyal reader of Skeptophilia, lived in Antarctica on the order of fifty million years ago.  The entire order was around for a very long time -- they first evolved shortly after the Cretaceous Extinction 66 million years ago, and only went extinct at the end of the Pliocene Epoch, three million years ago.  So these enormous toothed birds (pardon me, pseudotoothed birds) were swooping around scaring the absolute shit out of everyone for about sixty times longer than humans have even existed.

"In a lifestyle likely similar to living albatrosses, the giant extinct pelagornithids, with their very long-pointed wings, would have flown widely over the ancient open seas, which had yet to be dominated by whales and seals, in search of squid, fish and other seafood to catch with their beaks lined with sharp pseudoteeth," said Thomas Stidham of the Chinese Academy of Sciences, who co-authored the study.  "The big ones are nearly twice the size of albatrosses, and these bony-toothed birds would have been formidable predators that evolved to be at the top of their ecosystem."

It's easy to look around at today's chickadees and warblers and think of birds as being small, feathery, fluttering creatures who are more often prey than predator.  But even today we have, as a reminder that birds are dinosaurs, species like cassowaries:

[Image licensed under the Creative Commons Nevit Dilmen, Darica Cassowary 00974, CC BY-SA 3.0]

Which are as foul-tempered as their expression suggests, and have been known to attack people by kicking them with their heavy, razor-taloned feet.  So it's not just the prehistoric birds that have as their motto, "Do not fuck with me."

Anyhow, that's today's installment from the "Be Glad You Live When And Where You Do" department.  As fascinating as I find prehistoric life and birds in particular, I'd prefer not to meet in person a bird that could carry me away and eat me for breakfast.  

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