Avian ritual of 'anting' still a puzzle for scientists

ANOTHER LIFE:THE EARLY-MORNING blackbird on a cobbled patch in the garden was engaged in a strange avian exercise. It was dipping its beak to the ground, then plunging it among its feathers, first of one spread wing, then the other. Its tail was twisted over as it teetered for balance and there was obviously something very tense, even frantic, going on.

The bird was “anting” – plucking ants from between the stones and wiping them through its plumage. More than 200 species of songbirds are said to go in for this, all over the world, but the sight was new to me. And scientists still don’t agree about its purpose.

Thrushes, including blackbirds, are well-known anters, often using the common black ant of Irish gardens, Lasius niger– one of many species that spray formic acid as a defence. This toxic, corrosive chemical kills feather mites, chewing lice and ticks, which might seem a perfectly adequate reason for using angry ants as aerosol fumigants. Some birds, indeed, go in for "passive" anting, snuggling down into an ant's nest and spreading out their wings to be sprayed.

Experiments to prove what’s happening are still, however, quite few, and other hypotheses have ranged from auto-erotic stimulation (this, one presumes, from a young male researcher) to wiping the acid off ants before eating them. But most ideas have to do with general feather maintenance and self-medication – if not to get rid of parasites, then as a supplement for antibacterial preening oil or a control for fungal infections.

Rooks and jackdaws, perhaps for similar purposes, are given to spreading their wings while perched on smoking chimneys – behaviour reported by recent contributors to “Eye on Nature”.

The theories have been complicated by the variety of other materials, besides ants, that some birds wipe through their feathers. For American blue jays to use bombardier beetles, with toxic jets, makes parallel sense. But wiping with discarded cigarette butts suggests remarkable knowledge of nicotine as a pesticide, and a similar use of marigold flowers or the oil-rich peel of oranges or limes is a fascinating chemical refinement.

Strangest of all must be recognition by American grackles and European starlings of the repellent virtues of naphthalene mothballs, picked up and held in the beak with some difficulty but wiped up and down the feathers in just the same way, then dropped again. What all this says about the sense of smell in birds and their inheritance of chemical cues – expressed, perhaps, even in the plants they choose to line their nests – is rich ground for study.

The blackbirds, meanwhile, are taking advantage of the ever-open doors of the polytunnel and – I trust – feeding on its colonies of ants.

These are a dark-red sort, Myrmica ruginodis, one species of a tribe that, rather than spraying acid, has kept its capacity to sting. By edging the raised beds in the tunnel with forestry spruce logs, now slowly rotting, I unwittingly created the perfect habitat for its nests. Given the ants’ disposition to climb everything in sight, with my jugular vein one of their destinations, the tunnel is now something of a war zone. Borax powder from the chemist is my one controlling weapon.

This is the time of year for Irish populations of ants, notably the black ones of urban parks and gardens and the yellow meadow ants, Lasius flavus, of the countryside, to take to the sky in swarming nuptial flights.

For Dubliners, a muggy afternoon in late July or early August can bring a sudden aerial presence – not so much of the ants themselves (though they can sometimes look thick as smoke), but of wheeling flocks of birds that are feeding on them: swifts, swallows, starlings and gulls. Glance around at the ground at this time and you may catch the glitter as ants pour out of their nests, equipped with shiny wings, for the chance of a once-in-a-lifetime copulation in the sky.

The wonder is the extraordinary synchrony of the flights, over wide areas, involving millions of ants from thousands of colonies of the same species, over the same two or three afternoons. They are triggered by an internal body clock, along with particular climatic conditions: low windspeed, high humidity and a matching warmth between the nest and the air just above the ground.

By bringing together young virgin queens and males from miles away, the species avoid inbreeding. The males are dead within hours, but the queens, often mating several times with different partners, spin back to earth and cut off their wings. They have stored enough sperm to keep laying thousands of eggs underground for the next 10 to 20 years.