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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Big voices

One of the funniest scenes in the Monty Python movie Life of Brian is when a man is condemned to be stoned for saying "Jehovah," and the High Priest (played by John Cleese) is facing a crowd which is already armed with stones, ready to carry out the sentence.  The crowd, unbeknownst to the High Priest, is made up of women (who by law are forbidden from being there), and it's even funnier because that means the crowd was men playing women who were pretending they were men.

Well, at one point in the proceedings, the High Priest says the word "Jehovah" and gets clunked in the head by a rock.  He then demands to know who threw the rock.

A chorus of high-pitched, pseudo-feminine voices shouts, "She did!  She did!  She did!... um...."  (continuing in deeper, masculine voices)  "He did!  He did!  He did!"

This was the first thing my rather loopy brain thought of when I read a paper yesterday in Biology Letters.  In "Acoustic Allometry and Vocal Learning in Mammals," by Maxime Garcia (of the University of Zurich) and Andrea Ravignani (of the Max Planck Institute for Psycholinguistics), we find out that "dishonest signaling" -- using a voice that makes you sound bigger or more threatening than you actually are -- has been found in dozens of mammalian species.

The authors write:

Vocal production learning (VPL) can be defined as the experience-driven ability, rare among mammals, to modify existing vocalizations, to produce novel sounds or to imitate sounds that do not belong to an individual's vocal repertoire...  VPL inherently involves modulation of acoustic features related to the source, filter or both.  Yet, different species have varying degrees of control over the anatomical components involved in phonation.  For instance, despite a generally assumed lack of vocal control some non-human primates might have limited sound production plasticity, including for non-voiced sounds.  While the presence of VPL in non-human primates is debated, strong evidence for VPL has been found to date in humans and four other mammalian clades: non-otariid Pinnipedia, Elephantidae, Chiroptera and Cetacea.

"If you saw a Chihuahua barking as deep as a Rottweiler, you would definitely be surprised," said study co-author Andrea Ravignani, in an interview with Science Daily.  "Nature is full of animals like squeaky-Rottweilers and tenor-Chihuahuas...  Some animals fake their size by developing larger vocal organs that lower their sound, which makes them sound larger than you would expect.  Other animals are good at controlling the sounds they produce.  Such strategies -- 'dishonest signaling' -- could be driven by sexual selection, as males with larger body size or superior singing skills (hitting very high or low notes) attract more females (or vice versa)."

I know one good example of little animal/big voice from my own back yard -- the Carolina Wren (Thryothorus ludovicianus).  It's a tiny thing, what birders call an "LBJ" (Little Brown Job), but its outsized shriek of "TEAKETTLE TEAKETTLE TEAKETTLE" frequently wakes me up at four in the morning during the spring and early summer, especially given that there's one of 'em who likes to sing from the branches of the box elder tree right outside my bedroom window.  But this is volume, not pitch.  For misleading pitch, there's none that can compete -- at least in the bird world -- with the Great Potoo (Nyctibius grandis) of the rainforests of South America.  Take a listen to this:

Since this bird is nocturnal, and (as you can see) is very cryptically colored, a lot of the natives didn't realize that sound was a bird for a long time.  Their explanation -- that there was a horrible monster out there in the forest roaming around at night -- is completely understandable, given what its vocalizations sound like.

So the capacity to create misleading sounds isn't the sole provenance of the Monty Python crew's fake falsettos.  There are lots of animal species that do the same thing, either to frighten off potential predators or to sound sexier for potential mates.

Or, perhaps, to give a misleading answer to questions like, "Are there any women here today?... good, very well then."

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This week's Skeptophilia book recommendation of the week is for anyone who likes quick, incisive takes on scientific topics: When Einstein Walked with Gödel: Excursions to the Edge of Thought by the talented science writer Jim Holt.

When Einstein Walked with Gödel is a series of essays that explores some of the deepest and most perplexing topics humanity has ever investigated -- the nature of time, the implications of relativity, string theory, and quantum mechanics, the perception of beauty in mathematics, and the ultimate fate of the universe.  Holt's lucid style brings these difficult ideas to the layperson without blunting their scientific rigor, and you'll come away with a perspective on the bizarre and mind-boggling farthest reaches of science.  Along the way you'll meet some of the key players in this ongoing effort -- the brilliant, eccentric, and fascinating scientists themselves.

It's a wonderful read, and anyone who is an aficionado of the sciences shouldn't miss it.

[Note: if you purchase this book using the image/link below, part of the proceeds goes to support Skeptophilia!]