Naturespeak A naturalist's view of the world

May 27, 2009

The Gray Matter of a Blackbird

Filed under: Uncategorized — wykes @ 9:20 pm

I was speaking to a group of gardeners last week about spring things like walnut flowers, woodcock dances, and the miraculous generation of baby possums.  One of the things I mentioned was the curious case of a red-winged blackbird with half a voice. “It was a handicapped bird with a head wound,” I said, “and it could only produce half a call.”  The group uttered a spontaneous and compassionate “awww…” upon hearing this. The intensity of the reaction took me by surprise, so I jumped on the sadistic opportunity to state that the creature then died right in front of me, fell from it’s tree-top perch, and landed stone-cold dead on the ground – at which point I kicked it’s lifeless form into the shrubbery and callously walked away.  This, of course, was not true, but the moment of shocked silence was a wonderful thing to behold. “No,” I quickly reassured them, “Handicapped does not mean helpless and weak. This bird appeared to be doing fine and, as a matter of fact, had a wife!” Shock turned to laughter and relief as they asked for the details.

I came upon that half-song bird on a blustery warm day at Crosswinds Marsh. I was listening to the twitterings of a marsh wren when a loud unidentifiable call accosted my ears from  behind. Though the sound had a familiar ring to it, the manner and deliverance were odd. A lone male red-winged blackbird was perched high atop a stubby maple at the point where the sound came from.  The call was vaguely red-wing like, but not enough to make me say that this bird was the culprit. No other bird was in sight or sound, however, so I focused on him.

True to his sex, the creature started to issue the standard “check” call – which is a sort of warning call. Unlike the usual robust call produced by this species ( listen to the full warning call of another bird on the same day), his call was thin and tinny ( listen to his warning call).  The sound was, at times, lost among the hefty gusts of wind that circled about us. The thin-voiced male was persistent and, oddly enough, hung around in spite of my presence. No matter how close I got, he stayed put. The usual red-wing ploy is to chat away and then fly off to a distant perch, but this guy was acting somewhat docile.

I was able to take a few shots of the bird as it called and rode the swaying branch (see above). It was then that I noticed that it had a distinct notch in his head feathering. After it finally switched positions and landed on a nearby cat-tail, I took one more shot and could plainly see that exposed patch on the bird’s head. It seemed to have a head wound of some sort (see below).  When the bird finally belted out that odd grouping of syllables that I’d heard initially, I knew this was the bird in question.

About the only way I can describe that particular call is that it sounded like half a call – the duration was full but the quality was halved. Red-winged blackbirds usher the familiar bubbly “Oakalee-a” call as a vocal territorial marker, and they employ a unique blend of duel harmonics to give their calls a rich tonal quality. Try as I might, I was only to capture a brief snippet of this “half call” vocalization (listen to Partial Call here). My audio equipment actually caught a bubbly chortle that I hadn’t noticed before.

Since I never got a chance to examine this bird as a lifeless little corpse, I can only surmise that the quality of this blackbird’s song was somehow related to the head wound. Songbirds have a divided syrinx which, unlike our voicebox, divides into two “instrumental” parts. Sound frequency and amplitude is produced by a controlled air flow. Amazingly, these two halves can be separately controlled in order to produce two parallel harmonic lines. In other words, birds can harmonize with themselves.

Each side is controlled by separate nerves, referred to around the water cooler at the bird biology lab as the ipsilateral tracheosyringeal branch of the XIIth cranial hypoglossal nerve. Interruption of one of these nerves will shut down one element of the song production. Damage to one side or the other will cause missing harmonics, lowered volume and other such aberrations.  In layman’s terms, I suppose you could say that the song is cut in half. Since this nerve control originates in the brain, it would not be that startling to say that the head wound in evidence on this bird was sufficient to damage this connection.

Without any further evidence, I’ll have to leave the case of the half-voice blackbird right here. I am happy to report that this male had a mated female in his territory and it was a normal female to boot. In the harsh judgment of nature, handicaps – even small ones – are not usually tolerated, but apparently the fates do occasionally turn away their glance.

No Comments »

No comments yet.

RSS feed for comments on this post. TrackBack URL

Leave a comment

Powered by WordPress