Silvereye Sopranos

Today’s song (© Department of Conservation) comes straight from the beak of the Silvereye (Zorsterops lateralis). And the gorgeous art work above is © Lauren Delora Sears.

Every year, in the wee hours of a Sunday morning, we observe the small ritual of putting our clocks back an hour. It signals the end of warm summer evenings and mentally prepares us for the crisp autumn bite. This year, my partner and I were noisily woken up to attend another ritual – a fire drill. We stumbled about, bleary-eyed, searching for suitable garments to wear so we could head for the exit, half-decent. We gathered with the other 80-odd residents of our college, in the drizzle, at the designated area in the carpark. The fire brigade turned up soon after and checked out the building while we huddled together for roll call. Formalities complete, we were ushered inside and all of us trooped back to bed.

It was about 5.15am by the time we returned and we had been up just long enough to make it hard to get back to sleep. So I let my mind wander. I thought of the intensely glorious colours that autumn brings in this part of the country precisely because of the cold. In the hills, the ground crunches underfoot and frosty tussock twinkles in the early morning light. Across the paddocks, near where I used to live, the roar of the stags would carry easily in the still night air. But, even better, is the arrival of the flocks of silvereyes (Zosterops lateralis) to the garden each April.

These little birds are unbelievably cute. In New Zealand they are also known as waxeyes and are named for the small ring of white feathers encircling each eye. Silvereyes are members of the Passeriformes – perching birds with specific toe and leg arrangements to help them perch on flat surfaces. Passeriformes also have the most developed songs and are informally known as the songbirds. They are the ones happily singing away as part of the dawn chorus.

Birds have been heard to increase the pitch of their songs and calls in noisy urban environments compared with their rural counterparts. There seem to be two main theories to explain this. The first, is that the birds sing higher because the lower pitch vocalisations can be masked by low frequency noise from human activities. The second, is that the pitch is raised as a result of singing louder. This is also known as the Lombard effect and it occurs in humans as well.

Recently, scientists from Australia have carried out experiments to try to find out which of these is more likely. And those adorable silvereyes, who are known to increase their pitch in urban environments, were centre stage! They exposed rural and urban birds to both low and high frequency background noise and noted the responses. If the birds were trying to sing above the noise by singing louder, and that happened to raise the pitch, they would do so no matter what the frequency of the background noise. However, if they were trying to adjust their frequency to stop interference, they would raise it in the face of low frequency noise but lower it during bouts of high frequency noise. The result? It seems the silvereyes are pretty adaptable and can adjust up or down as they need to.

Regardless of the pitch of their songs, I’m looking forward to seeing them later in April when they come into my garden to raid the urban larder. Who can resist those faces?




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