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Drama at the Nortel wetland

Yesterday in the Nortel woods, I was walking along where some stones traverse a wet spot on the path, and heard a Sedge Wren singing. Sedge Wren is a small, shy and secretive bird, rare in Ottawa. It would be a lifer for me, so I spent some time trying to spot it, without success.

At some point, I saw one bird chase another out of the area. The chaser was a Common Yellowthroat. I couldn't tell who the chasee was, but after this occurrence, I didn't hear the wren sing again.

Today I went back armed with my IPod, and attempted to call the wren out (if it was still around) by playing its song. It never responded. I did get a response though--a big one! Common Yellowthroats in the area became agitated. They're normally skulkers (though not as secretive as Sedge Wrens) in thick vegetation, but as soon as I started playing that song, I had multiple yellowthroats popping up into the trees in plain view, looking around, scolding, and then singing at the top of their voices. I got some of the same reaction from nearby Swamp Sparrows.

One thing some people don't realize is that, while birdsong sounds cheerful to us, it's actually somewhat aggressive. It's an expression of self-assertion and fitness: "this is my territory and I've got what it takes to defend it." (Think of how much energy it takes to sing all day, as some birds do. Or how much guts it takes to do something that draws attention to yourself when you're a small bird surrounded by potential predators.) So the beautiful golden-throated bird popping into a tree and singing a bright, happy-sounding "witchety witchety witchety!" was the avian equivalent of a man flexing his biceps and saying, "oh yeah? Well check this out." (I even noticed an increase in general skirmishes, none of them involving wrens: birds chasing each other around, and such. It had the feel of a bar brawl. "Who, me? I didn't say it!") In fact studies have shown that birds' testosterone levels skyrocket when they hear the song of another of their species in their territory.

But this was a case of cross-species aggression, and, together with yesterday's event, suggested that Yellowthroats consider Sedge Wrens to be direct competitors. It made me wonder: could it be one of the reasons Sedge Wren is so secretive, uncommon and local (breeding in certain places one year and then gone the next) is because it can't stand up to other birds who share its habitat (sedge marshes and wet meadows)? It's 4 and a half inches long, which is smaller than most. Just an off-the-cuff theory.

The Wikipedia page gives me an idea of why a Sedge Wren might not be such a popular neighbor. It says, "he may puncture the eggs of other birds nesting nearby"!

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Mustang Sallie
May 18th, 2012 at 10:27 pm
You must have been a bird in a past life!

May 19th, 2012 at 11:20 am
That does sound rather unneighborly... why would it puncture their eggs? To try to maintain access to food in the area by making other birds abandon their nests?

May 24th, 2012 at 7:03 pm
I totally understand and believe that bird song is aggressive, in a similar vein to lions growling, dogs barking, and cats hissing. They are not singing to make pretty music for us to enjoy and appreciate.