Sing when you're winning: how birds size each other up

ANOTHER LIFE:A SOUTHEAST wind has to squeeze through the mountains, first Connemara's Twelve Bens and then the Sheefrys and Mweelrea on our side of the bay. At gale force, the wind can emerge in bullying, even frightening, gusts, but at other more steady, if still wintry, volumes it just plays games with the clouds.

“Where stable, moist air flows over a mountain or a range of mountains” – this from Wikipedia – “a series of large-scale standing waves may form on the downwind side. If the temperature at the rest of the wave drops to the dew point, moisture in the air may condense to form lenticular clouds . . . Under certain conditions, long strings of lenticular clouds can form near the crest of each successive wave.”

Thus, at dawn the other morning, with the summit of Mweelrea lost in a cloud of its own, a whole line of UFOs – lenticular = lens-shaped, as you knew – trailed away across the sea, each gauzy saucer gilded by the rising sun. Even with Wikipedia’s meteorology on tap, I felt a druidic shiver of delight.

Must science always intrude on magic, begging for explanations? On the UFO morning, a cock blackbird was singing from the summit of a hawthorn bush, its bill the same bright gold as the cloud above the mountain. The full territorial concerto, fluent, supple and elaborate, held me marvelling as I stooped above the rain gauge.

But again, of course, the questions insisted: how much instinct, how much learning and choice? The literature on birdsong began with Aristotle – “In general, the birds produce most voice, and with most variety, when they are concerned with mating” – and has proceeded in modern times, via the sonogram, to ever-more refined acoustic and behavioural deconstruction.

The male blackbird, indeed, now has a literature all his own. Much of it currently reports on the research of Dr Torben Dabelsteen, an evolutionary biologist at the University of Copenhagen who probes the purpose, structure and effect of the cock blackbird’s song and evolution’s selection of its qualities for defending territories, winning mates and so on. With postgraduate teams to help, he uses acoustic gadgetry in blackbird woods and gardens to intervene in the birds’ dawn chorus and see how individuals respond.

“If I were a blackbird, I’d whistle and sing . . .” The whistling that launches the blackbird’s territorial song is a far-carrying “omnidirectional” announcement, meant for other cocks, and the twittering that often ends it is for strictly local consumption, a measure of excitement intended, perhaps, for females listening in the undergrowth. The main melody is meant for other males but is by no means a standard performance. Indeed, the Danes had to analyse more than 200 songs to estimate a male’s repertoire, which averaged 44 different musical phrases, or motifs.

Most of these are learned by young birds from communal song, but while many start-up motifs are shared between the birds, perhaps a dozen in the middle are highly individual and perfected by practice. Entire songs are only occasionally repeated, but these motifs are always sung in the same order.

Theory supported by several studies had predicted that the size of a cock blackbird’s repertoire lets potential rivals judge each other’s fighting ability – “an honest signal of male quality”, as the Danes put it.

Indeed, Dabelsteen had already found a match between body size and size of song. So this might be important for natural selection of the “fittest” birds, not only for male-male competition but also for female choice of a mate.

In 2010, on the German island of Heligoland, there were 80 breeding pairs of blackbirds. In “a territory intrusion playback experiment”, Dabelsteen’s team removed some of the territorial males and installed loudspeakers in their place.

These broadcast recorded songs of different repertoires and sizes and assessed the responses of neighbouring cocks. To Dabelsteen’s surprise, they didn’t seem to tell one from another: size, after all, wasn’t everything.

That won’t, of course, be the end of it. Female canaries, apparently, choose males with “sexy syllables” that take a lot of energy to produce. Perhaps it’s some of these, embedded in the blackbird’s individual phrases, that come to matter most in the nest.

My blackbird, as it happens, was singing all alone, not even bothering to twitter before diving back down from his perch on the hawthorn. Maybe he was just rehearsing ahead of time – perhaps led astray in January by three fine days together and my alexanders, a Mediterranean herb, already in tentative bloom.

Nothing seems all that extraordinary now, not even a sky full of jellyfish, UFOs or gilded, lenticular clouds.

Eye on nature

We used to have a population of between 10 and 16 hares on the farm, but now we are lucky if we see one or two in a week. Could it relate to the increase of the buzzard population in the area? A very large raptor crossed my yard recently.

Patrick C Cooney, Carpenterstown, Co Westmeath

Buzzards might take tiny leverets but not full-grown hares. A white-tailed eagle might, however. The decline in hare numbers has been blamed on changes in farm practices, hunting and coursing.

On Ballisodare Bay, in Co Sligo, my attention was drawn to the shrieking of a distressed red-breasted merganser. It was being propelled by an otter that subsequently dropped it and disappeared up the beach. Is it common for otters to attack seabirds or was it killing a rival?

Trevor Hunter, Knocknahur, Sligo

Yes, otters do prey on waterbirds and seabirds.

In the middle of our lawn for 10 minutes, two rooks faced up to each other six inches apart, wings horizontal, mood totally aggressive. One rook had a feather in its beak. Could this be early male mating competition?

Jim Dixon, Ballincollig, Co Cork

Yes, or quarrelling over territory.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie.

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