An innocent flight for the murder of crows?

ANOTHER LIFE: WHY DO blackbirds think I want to murder them? Of all the birds that come to the box of oatmeal on my study windowsill, Turdus merulais the biggest and most aggressive, bullying even the song-thrush, yet its eye must not catch mine across the word-processor or it's off. As for opening the front door, away it whirrs under the hedge, screeching in shock and alarm.

There are, as I shall be told by readers, quite other blackbird experiences –­birds that are called to be fed from the hand, or that bring their young into the house each year to have their picture taken on the kitchen mat (both in Mark Cocker's Birds Britannica). But their generally highly-strung behaviour is undeniable. Even St Kevin, with his arm stuck out the window at Glendalough, must have been waiting for hysterics to erupt from the bird nesting on his palm. ("Are his fingers sleeping?" wondered Seamus Heaney. "Does he still feel his knees?") More to the point ecologically in a rigorous winter, with every scrap of food hard-earned, is the cost in energy of such superfluous alarm.

Needless fright is also common among the little birds that flee our nut-feeders on any human approach. Cats, stoats, foxes –­ all these could mean predatory harm, but big people in fluffed-up coats and woolly hats? It is, after all, some time since anyone put a pie-crust over four-and-twenty blackbirds, even for “Come Dine With Me”.

Blackbirds brought their terror from the forest floor: look how they rummage, scattering fallen leaves –­ or oatmeal –­ in all directions with one beady eye on the shadows. In Britain, as late as the mid 19th century, the blackbird was still a bird of woodland and unknown as a nesting bird near houses. In Ireland it was dispossessed of woods far earlier, adapting to gardens, farmland and hedgerows and even to the virtually treeless islands of the west. That fear of humans had to be acquired was certainly Charles Darwin’s belief. He wrote how, on the virgin Galapagos, “I pushed a hawk off a tree with the muzzle of my gun, and the little birds drank water out of a vessel which I held in my hand.” Many naturalists have noted how, in long-inhabited countries, the most timid of birds adapted quickly to roaring monsters of trains or new motorways but flew from any figure on the skyline.

In changed times, do they never unlearn their fear? An American team recently studied Stress and the city: urbanization and its effects on the stress physiology in European blackbirds. They hand-raised urban and forest-living blackbirds under identical conditions and "tested their corticosterone stress response" every few months. The city birds had a lower stress response than their arboreal cousins. Such adaptation, the team suggested, may be ubiquitous among wildlife in towns.

In Spain, three ecologists produced a recent paper: To run or to fly: low cost versus low risk escape strategies in blackbirds. It was based on "simulated predator attacks" on blackbirds in four wooded parks in Madrid . The researchers – with permits – advanced on the ground-foraging birds at a steady speed of one metre per second (whether they waved their arms isn't stated) and noted the distances at which they ran, or flew, and how far they went.

From 203 such sorties they concluded that blackbird decisions on whether to run or fly depends on when they choose to escape, and that if they fly, which takes more energy, they go further – all of which makes sense. Juvenile blackbirds flew more often, perhaps for fear of making the wrong choice, and adults flew more often in the afternoon, when they are heavier from feeding, choosing more rapid safety at greater cost in energy.

Blackbirds, often solitary, can make up their own minds –­ but how do flocks of birds avoid wasting good feeding time by false alarms from fidgety and watchful individuals? A British team, led from Oxford University, sought “Evidence for a rule governing the avoidance of superfluous escape flights” by lengthy videoing of the behaviour of flocks of redshank as they were attacked by sparrowhawks – or not, as the case may be – at a saltmarsh in Scotland.

In one study of more than 900 alarm flights, more than three-quarters of them were unnecessary –­ the approaching bird was not a predator, or there was no apparent cause for alarm. But still, one rule of thumb became clear. Departure of a single bird might rouse some curiosity (the redshank has no alarm call), but only the simultaneous flight of a number of birds would trigger immediate response from the flock.

Like the blackbird, they clearly spend a lot of time –­ and energy ­– getting things wrong.

EYE ON NATURE

I have seen the corncrake that we rescued last December (Eye, 09/01/10) alive and well in mid-February, and a few hundred yards from where I released it. A good survivor considering the weather and the number of birds that died.

J Carmody, Kilrush, Co Clare

Recently at Swords Estuary, I saw a bar-headed goose. It was quite happy among the swans and mallards.

Patricia Saul, Swords, Co Dublin

A bar-headed goose was seen this time last year also at the Swords Estuary. A native of Central Asia, it is probably an escapee from an aviary or fancier.

On Belfast Lough shore I watched a hooded crow flying up and repeatedly dropping a mussel shell on the car park until it opened. Has this behaviour been noted previously or are Belfast crows smarter than their country cousins?

Michael Flanigan, Belfast

Crows and gulls have been breaking shells in that way since time immemorial. The trick is even recorded in Aesop’s Fables in The Eagle and the Crow.

Around midday on March 7th, a beautiful sunny day, I saw a small tortoiseshell butterfly flying around the garden. I presume it was an early awakened hibernator.

Florence Shields, Clogherhead, Co Louth

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo. E-mail: viney@anu.ie. Please include a postal address.