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Category: Song learning

George the Sparrow

George the Sparrow

Ian Cruickshank of Victoria, BC sent me a remarkable recording of a very confused Song Sparrow, which seems to be incorporating the complete song of a Northern Waterthrush into its own singing.  Here’s the recording on Xeno-Canto:

When I first heard the recording, I thought the bird could be a juvenile using some imitations in its subsong — a decent possibility, given the late September date  — but the comments Ian sent me about the recording seem to rule that out:

I first heard this Song Sparrow giving this song phrase in April of this year; I didn’t manage to record it at the time and it was a stroke of luck that I came across it again, engaged in a territorial match with another male Song Sparrow, belting out this song in the exact same location, in September this year. Obviously it’s a resident bird.

Let’s compare spectrograms.  Here are a couple of excellent recordings of Northern Waterthrush songs.  Note that waterthrushes, like Song Sparrows, have numerous song dialects across their range:

Here’s a spectrogram of one strophe of Ian’s weird Song Sparrow.  Because the other birds on the recording make the spectrograms difficult to read, I’ve highlighted the Song Sparrow song in the background by coloring it red (a la The Sound Approach):

The last four (red) notes on the spectrogram are pure Song Sparrow, but boy, the rest of it sure looks like Northern Waterthrush, with the classic pattern of three contiguous series, including the rapidly downslurred whistles at the end. I think it’s highly likely that this Song Sparrow, during the “critical period” in which it was listening to the songs around it and piecing together its repertoire, mistook a Northern Waterthrush for a legitimate Song Sparrow tutor.  This phenomenon is rare in Song Sparrows, but not unprecedented.  Here’s what the Birds of North America account has to say about it:

Species displays innate preference for learning con-specific song and, like other Emberizidae, rarely mimics other species. Song Sparrows exposed to natural Song and Swamp Sparrow song in lab preferred strongly to learn conspecific song, but sometimes sang syllables of Swamp Sparrows (Marler and Peters 1987, 1988). Song Sparrows fostered by canaries (Carduelinae) did not mimic foster parents in one study (Mulligan 1966) but copied some elements in another (Kroodsma 1977). In contrast, Eberhardt and Baptista (1977) suggested Song Sparrows imitated Wrentit (Chamaea fasciata) syllables in wild, and Baptista (1988) recorded a Song Sparrow in San Francisco, CA, that produced White-crowned Sparrow song; another bird at Tioga Pass countersang White-crowned Sparrow song with neighbors of that species (M. Morton pers. comm. in Baptista and Catchpole 1989).

Song acquisition has been pretty well studied in Song Sparrows, and we know a lot about how they put together their repertoires.  When they are raised in the laboratory with adult tutors of their own species, they usually tend to copy whole songs verbatim. They also prefer to copy the songs that are shared by multiple tutors — in other words, they seem predisposed to learn the most popular local tunes.  However, some Song Sparrows act differently; one bird invented all its own songs, and several others tended to recombine elements from multiple tutor songs in creating their repertoire.  Ian’s sparrow most likely did the latter: it was trying to invent a new Song Sparrow song using elements of other Song Sparrow songs it had heard, but it misidentified one of its tutors and ended up with a weird, chimeric melody.

Now that it is an adult bird, it’s likely to sing this hybrid songtype for the rest of its life.  It’s hard to say whether that will disadvantage it.  Various studies have measured Song Sparrows’ responses to abnormal songs (including, among others, artificially constructed songs that arranged Swamp Sparrow syllables according to Song Sparrow syntax, and vice versa), and the findings tend to agree that imitations or corruptions of Song Sparrow songs elicit weaker responses than typical songs, but they still elicit responses.  Thus, this abnormal song likely won’t be as effective in driving away a rival male or attracting a female mate, but it may get the job done.  If, like most Song Sparrows, this individual has between 5 and 13 different songtypes in its repertoire, then the weird waterthrush-song might only be deployed between 8% and 20% of the time.  Assuming it’s the only abnormal songtype in the repertoire, it might not prove a huge disadvantage to the singer.

If this bird maintains a territory over multiple years, there’s a chance that juvenile Song Sparrows moving into nearby territories might even select it as a tutor, adding some or all of the Northern Waterthrush syllables to their own songs second-hand and potentially propelling them into the local Song Sparrow vernacular in the long term.  A similar process might explain why, for example, so many of the “Thick-billed” Fox Sparrows in the Sierra Nevada end their song phrases with what appears to be a straightforward imitation of the “kleer” call of Northern Flicker:

However, I think this unlikely to happen among Vancouver Island Song Sparrows.  Song Sparrows seem much less likely to imitate than Fox Sparrows, which means Songs probably have a stronger (though not ironclad) genetic mechanism to guide young birds to ignore the syllables of other species and incorporate only their own.  My prediction: this wrong-singing sparrow might not be a complete pariah, but in the long run he probably won’t prove a strong competitor for territories and mates either, and his borrowed syllables are unlikely to impress the next generation to follow in his footsteps.  He’s a slightly socially inappropriate, oddball schmo: the George Costanza of Song Sparrows.  We’ll call him George for short.

Humming Their Own Tune

Humming Their Own Tune

In the bird world, there’s usually a pretty big difference between vocalizations that are learned and those that are not learned. By and large, learning birds can produce much fancier songs than their learning-impaired cousins – perhaps because coding music directly into the DNA takes up a lot of genetic “disk space,” introducing limits on the complexity of genetically-determined vocalizations.

Like many members of its family, this Anna's Hummingbird sings an extremely complex, learned song. Photo by Nathan Rupert (Creative Commons 2.0).

If you flip through a North American field guide, you might notice that the birds in the front half of the book (ducks, hawks, owls, gulls, woodpeckers) tend to have pretty simple vocalizations, whereas all the most acclaimed avian singers (wrens, thrushes, finches, mockingbirds and thrashers) are in the second half of the book. This is no coincidence. First, birds in the order Passeriformes (the huge order that encompasses the second half of the field guide) sport a uniquely complex set of muscles to control their syrinx, enabling them to perform much more spectacular feats of vocal gymnastics. Second, with the important exception of the flycatchers, most North American passerines learn their songs.

However, the learning of complex songs isn’t restricted to the so-called “songbirds.”  In fact, some of the best examples of learned, complex songs come from a family that isn’t in the Passeriformes at all: the hummingbirds.

To people in most parts of North America, this may come as quite a surprise.  That’s because our most widespread and familiar hummingbirds — Ruby-throated, Black-chinned, Broad-tailed, and Rufous — actually don’t sing songs at all; their vocalizations are limited to a variety of chip notes and buzzes, and produce their territorial sounds mechanically, with trilling wings or chirping tails in display dives.  But to those who live along the West Coast or in the southwestern deserts, the soft but astonishing song of the Anna’s Hummingbird is a familiar sound:

And Anna’s is no fluke.  Behold the vocal stylings of a Green-throated Mountain-Gem, a Central American relative of the Blue-throated Hummingbird:

Laboratory experiments have demonstrated that at least Anna’s Hummingbirds learn their songs, and as one would expect, the songs vary regionally as a result.  Although not all hummingbird songs are as complex as the examples above, the variation in songs can be tremendous.  Check out Xeno-Canto’s collection of recordings of Reddish Hermit, a lekking hummingbird from South America.  A quick perusal of nearly two dozen spectrograms will show that no two songs are alike.  Now, South America is a huge continent, and a species as wide-ranging and vocally variable as Reddish Hermit might well be split in the future — but take a look at these three recordings, all from the same biogeographic region (the Guianan Shield):

All show a similar repeated downslurred series, but each is spectrographically unique, and those differences are easily detected by the ear.  The differences are evidence of song dialects — local variants that we would expect to see in any population with learned songs.  (Anna’s and other singing hummingbirds have these song dialects too, but the differences between dialects are a little easier to see in a hummingbird with a simpler song.)

Many species of North American hummingbirds sing, including Costa’s, Blue-throated, Magnificent, White-eared, Broad-billed, Violet-crowned, and probably also  Buff-bellied.  In the tropics, the chorus of singing hummingbirds can sometimes be absolutely bewildering.  Next time you’re in singing hummingbird territory, keep your ears peeled for these all-too-often overlooked, underestimated melodies.

Song of Smudgy

Song of Smudgy

"Smudgy," the first documented hybrid Black x Eastern Phoebe, Larimer County, CO, 4/26/2007. Photo by Rachel Hopper; used with permission. Click to enlarge.

In 2007, an odd-looking flycatcher set up a territory above a diversion dam along the Big Thompson River in Loveland, Colorado.  It was clearly a phoebe, but what kind of phoebe, the first few observers couldn’t seem to decide.

Eventually, after puzzling over some internet photos of the smudgy-breasted bird, Nick Komar suggested that it could be a hybrid — one parent a Black Phoebe, the other an Eastern Phoebe.  As soon as Nick’s suggestion landed in my email inbox, I knew I had to get sound recordings.  For one thing, if it was truly a hybrid, then it was well worth documenting, because hybridization had never been reported among phoebes before.  For another thing, I knew that a microphone trained on a hybrid flycatcher would open a unique window directly into the bird’s genetic code.

Why?  Because unlike most other passerines, flycatchers don’t learn their songs.  In a series of classic experiments in the 1980s, Donald Kroodsma raised Willow and Alder Flycatchers and Eastern Phoebes in the laboratory and determined that even if they were raised hearing only the wrong songs, or even if raised in complete silence, the birds all grew up to sing almost exactly like their parents.

This does not happen with most passerine birds.  If you raise a finch or a junco without exposure to finch or junco songs, the bird might learn the wrong song, or it might grow up to sing incoherent babbles, but it definitely won’t sing like “normal” wild members of its species.  Most birds with complex songs need tutoring and time to learn them — but not flycatchers.  Every part of their vocal repertoire is somehow coded in their genes.  Which means that if the genes of two species were to mix, one would expect to hear some sort of hybrid song.

Here’s what a normal Eastern Phoebe sounds like:

Eastern Phoebe song, McCurtain County, OK, 3/22/2008.

And here’s a normal Black Phoebe:

Black Phoebe song, Humboldt County, CA, 3/27/2009.

Birds with innate songs don’t usually show much geographic variation; they don’t have regional “dialects” the way that, for example, White-crowned Sparrows do.  Therefore, in theory, Eastern Phoebes and Black Phoebes from all across their North American range should produce spectrograms that closely match the ones above.

That’s why, when I saw the spectrograms of the bird from Loveland, I knew we were dealing with a hybrid:

Song of hybrid Black x Eastern Phoebe, Larimer County, CO, 5/2/2007.

But “Smudgy,” as some of us called him, didn’t just mix up the pieces of Black and Eastern Phoebe songs.  His song behavior was even stranger than one might expect from a hybrid.

For one thing, while Black and Eastern Phoebes both usually sing by alternating two different songtypes, Smudgy had three to choose from — like a Say’s Phoebe, the only species in the genus that had not given him genes.  In addition, the introductory notes in Smudgy’s song were poorly stereotyped — that is, they weren’t always carbon copies of one another, but instead varied slightly with each delivery.  However, the terminal portions of his songs were stereotyped.  Furthermore, the different parts of Smudgy’s songs seemed to show different levels of influence from the parent species.

Why in the world would a hybrid sing like this?  To know for sure, we’ll need more recordings of hybrid phoebes.

Hybrids appear to be on the increase, particularly in southern Colorado and northern New Mexico, where the northeasterly range expansion of Black Phoebe has started bringing it into sympatry with the westward-surging Eastern — but an apparent Black × Say’s showed up in northern California, and it’s worth noting that “Smudgy” was found at least 150 miles outside the range of either of his parent species.  Since hybridity may well scramble the migration genes as well as the song genes, a hybrid phoebe may be possible almost anywhere on the continent.

In Cañon City, Colorado, smack-dab in the center of the contact zone between Black and Eastern Phoebes, SeEtta Moss has begun finding her own hybrid phoebes.  She recently posted photos [1 2] and  a video clip of a definite hybrid, as well as photos of another possible hybrid (perhaps a backcross).  Here’s the spectrogram of the definite hybrid (using the audio from her video clip):

Song of hybrid Black x Eastern Phoebe, Fremont County, CO, 4/9/2010. Audio from video by SeEtta Moss (click for link).

As you can see, this bird sings differently than Smudgy, which raises even more questions.  As our sample of hybrid recordings grows, we may be able to discover some really fascinating things — not just about how genes control song, but also about how song evolved in these birds.  More on that coming soon.