Stone the crows: the nuns who called in a hit squad

ANOTHER LIFE:THE MELLIFLUOUS TWITTERING of songbirds that attends my seed-sowing sessions in the polytunnel was rudely drowned out the other morning by a clamour of harshly disputatious noises from one of the trees that give the tunnel its shelter.

Our first nesting rooks were reminding me that they can make very noisy neighbours. Would we really welcome any more? At the time their tall sycamore was planted, about 30 years ago, a colony of some 50 pairs nested each year in the old sycamores around the farmhouse down the hill.

I could peer into the rookery as if into a Neolithic village, a circle of spiky nests wreathed in turf smoke from the chimney. The birds’ grand, wheeling processions against the afterglow of the ocean sunset were special of their kind.

Yet it was no great surprise when the rookery, erupting into raucous discourse as early as 4am, was eventually persuaded to vacate the farmstead, or for me to find that young men from such houses tend to build a new one of their own without wanting a tree in sight.

The many rookless years at least spared us the birds’ dawn raids on our potato ridges – a complaint, I note, shared by the Tipperary nuns who, in the War of Independence more than 90 years ago, beseeched the British army to come and shoot the birds. (Their letter will be auctioned in Dublin this coming Wednesday.)

The role of rooks on farmland – damaging, beneficial or both – has inspired a lot of research. Against their keen appetite for leatherjackets (the big, root-chewing grubs of the crane fly) and other insect pests, one must count the birds’ banqueting on fresh-sown grain or cereals in cornfields lodged by bad weather.

Irish farmers now complain that rooks tear holes in the shiny black plastic stretched over their bales of silage; some even paint big white noughts or crosses on the bales as a charm or communal deterrent.

A Teagasc survey found birds – mostly rooks – guilty of damaging bales on 63 per cent of Irish farms, leaving their droppings and footprints on the plastic and, by letting in the air, making the silage go mouldy. It made no conjecture on the birds’ motivation.

Nor did it offer any relationship between the incidence of bird damage and the presence or absence of rookeries – small rookeries are abundant throughout the well-hedged farming countryside, and virtually all baled silage is within reach.

The definitive study of Irish rooks is still one carried out 20 years ago by a young Scottish ornithologist, Ron Macdonald, for his PhD. A mark of his industry was a count of about 5,000 nests in 66 rookeries in 100sq km of Co Kildare.

Bringing technology to bear with something called (gloriously) an automatic adiabatic bomb calorimeter, he was able to show that, for a rook, one acorn packs as much energy as about 30 small earthworms (which is why they hide them as a takeaway reserve).

A typical rookery in Ireland might contain only a couple of hundred rooks, whereas some of those on the Continent have populations of thousands. They all, I suppose, have to start with one pair building an isolated nest, though single nests such as we have seem to be rare.

What, then, was the row about when I was in the tunnel? A subsequent rúisc of cawing soon after sunrise drew my binoculars to the treetop, where two rooks were whirling in a flurry of wings and a third – the female – was slipping back into the nest to sit on her eggs. The intruder retreated (perhaps for the umpteenth time), and the resident male resumed his perch as sentinel.

A UK study of rook breeding behaviour suggests a tabloid scenario. The posture of an incubating female can, it seems, be misinterpreted as solicitation by an unengaged and randy male.

Attempts at copulation occur most frequently, indeed, between birds that are not paired to each other and most often with an incubating female. They are usually countered by the rightful spouse – but imagine this carry-on in a colony of 50 nests.

Ireland’s rooks seem safe enough in numbers. Those in the North, indeed, actually doubled in the late 1990s, and Co Derry has the highest density of nesting rooks in these islands.

The conservation of other farmland birds – skylarks, yellowhammers and more – is of major concern and one of the topics at next month’s Bird Habitats Symposium, to be hosted on May 18th by the Royal Dublin Society, in Ballsbridge. Changes in climate and land management have implications for a great range of Ireland’s habitats, from rivers and reed swamps to upland heath and bogs.

Details of the Bird Habitats Symposium are at birdhabitats.wordpress.com

Eye on nature

Recently I dropped some worms out of the top of our composter on to the grass. A blackbird came, collected a beakful and flew off.

Alan Jones, Greystones, Co Wicklow

You have a problem with your composter if the worms moved to the top. The contents are either too acid or too wet. Keep citrus peel out of it.

On March 25th and 27th I saw ladybirds (yellow with black spots). I have never noticed them so early.

John Cosgrove, Crossmolina, Co Mayo

I was out with my daughter, looking for our six-month-old kitten, when we found a very lively hedgehog near the church. Do they normally stir out at night?

Noel Graham, Clondalkin, Dublin 22

Hedgehogs are nocturnal but can be seen at dawn and dusk out foraging for insects and earthworms.

I have seen bluebottles on flowers. I thought they were only attracted to carrion.

David Nolan, Santry, Dublin 9

Bluebottles feed on flower nectar, plant sap and other sugary materials, which they taste through hairs on their feet. When they find the substance acceptable they extend their proboscis and feed. Females lay their eggs in carcases and rotting meat so that the larvae can feed.

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie. Please include a postal address