Thursday, August 27, 2015

House Wren Mystery Unsolved

When common house wrens moved into my new $165 artisan bluebird house this summer,  I had to conjure up a benevolent attitude toward them at first. The wrens worked tirelessly to fit their sticks through the narrow entry hole. Nevermind that the house was constructed to discourage little brown birds and was priced accordingly. After many failures, dropped sticks, and continued tries, they learned to tilt their heads to give the sticks just enough of a vertical angle to fit through the oblong hole. Sometimes the sticks were too long at any angle. Those, they learned to poke end-first through the hole. To watch them was to be awed by their effort.  How could I begrudge them their desire for a nice home for their coming family?

Besides, while I love the self-effacing murmur of the eastern bluebird, nothing draws me to the backyard swing better than the tantalizing song of a male house wren in full mating mode. Constantly repeated and remarkably loud for such a tiny bird, his bubbly warble goes on for long seconds, impossible to imitate or describe or resist. Once you have intimate knowledge of the house wren's meandering aria, it becomes an instantly recognized favorite in the repertoire of the backyard opera.

So, bluebird issue aside, I resigned myself to enjoying the house wrens, and embarked on Nestwatch 2015, meaning one hour of meditation and outdoor observation per day on the backyard swing until the house wrens fledged. Things went as expected until a mystery developed that I still don't know the answer to and may never know. The wrens were nearing the end of their rightful nesting sequence. She had accepted his offer, laid her eggs, and tended them well. He flaunted his accomplishments near or atop the house. Whether boasting or protecting, I couldn't say, but he sang his heart out all day every day in the weeks from first attraction to the approaching day of fledge. By that time the nestlings' squawks, at first barely audible from inside their elegant house, were getting louder and more demanding every day. Both parents worked full-time from sunup to sundown bringing morsels of food to the doorway and carrying little white fecal sacs from the nest.

Then one morning, thinking the time of fledge was near, and not wanting to miss the exhilarating moment, I took up my watch on the swing before the sun was above the horizon. The sky had lightened, but the dawn chorus had not yet begun. I love being out early enough to hear the waking murmurs of the backyard birds during nesting season—low and soft at first, until suddenly one bird sings out, then all hell breaks loose, making it difficult to identify who is singing what from which corner of the yard.

On this particular morning, the quiet was first broken by the identifiable Mr. House Wren, who flew to his roof from somewhere in the woods and began his Pavarotti impression. Within a few seconds, Mrs. House Wren emerged from the house on a rapid-fire mission of fury. She pushed him off the roof with an angry sounding chit chit chit chit chit! She might as well have said, "You woke the babies, you bastard! What were you thinking? I've told you a thousand times not to start up that racket this early." She chased him across the clear space in the yard where they disappeared into the low bushes and continued their wild kerfuffle. After the noise died away, she flew back to the house, and he disappeared, never to return. Ever.

In the days that followed, she alone brought food to her little squawkers, but she couldn't seem to keep up with their demand. Was it my imagination that she looked thin and exhausted, that she came less and less often, that the tiny squawks got dimmer? Then one evening, about a week after the father had gone missing, the squawks became so weak I had to put my ear to the entry hole to hear them at all. The next morning the nest box was silent and entirely without activity. That's how it is after a fledge—instant stillness—but it doesn't usually happen so early in the morning. You can often spy the new fledglings hopping in the bushes and trees near the nest box for a few days afterward. Some years I've stuck around long enough to observe one of the adults return to clean out the nest box on the day of the fledge. But on this day, there was none of that. The quiet felt deadly and complete.

Fearing the worst, I was too squeamish to peek inside the house. I chose, instead, to go with the theory that I had simply missed the fledge. Yet the real mystery of why the father disappeared that day remains unsolvable. Why did the mother chase him off?  Did he stay away because of the chase, or did he come to some unknown harm, like cat or hawk?  The mystery seems all the more curious, because in the years I've been conducting my nestwatches, I've never known a father of a successful nesting venture to abandon ship before fledge time. dkm