The operation began cautiously, with small bands of volunteers lurking at either end of a long, flat expanse of parkland beside a lake that the geese frequent at Frampton on Severn. At 5.45pm I joined one gang of eight, under the direction of Stephanie Warren, a student from the Nottingham Trent University who is doing her PhD on these handsome and hefty but destructive birds.
For about a month at this time of year they are flightless, since they have moulted after breeding and are still growing new feathers. The Frampton flock knew that something was up, because earlier in the afternoon Steph and a few helpers had set out a wide-mouthed funnel of wire netting, leading into a small, circular corral.
H-Hour was set for 6pm. At our corner of the park stood a handsome, 18th-century entrance gate, flanked by ornamental stone walls, and as we skulked behind them, the geese waited warily in a solid mass on the bank of the lake some 300 yards away. Our aim, when we moved, would be to slip out along the edge of the water, which lay to our left, cut the birds off from it, and push them out over the open turf.
In whispers we discussed the habits of these geese, which live a life of ease. Not for them the long-haul migrations to and from the far north: this lot move only between Frampton and the Wildfowl and Wetlands Trust at Slimbridge, three miles downriver.
During the summer they graze on the grass in the park; in the autumn they move out on to stubble fields all around, and in winter they gorge on the corn put out at Slimbridge for those true long-distance commuters, the Bewick's swans, which have bred in the Arctic and flown home several thousand miles for the winter.
Since Steph worked at the Wildfowl Trust for four years, and since most of her helpers come from it, none of them cares to admit that Canada geese are really rather a pest; yet to a farmer like Rollo Clifford, who owns the land at Frampton, the birds are an infernal nuisance.
It is small comfort to him to be told by scientists that Canadas graze at only half the rate maintained by the smaller and nippier barnacles. The fact remains that they get through a tremendous amount of grass. If - as is generally reckoned - eight geese eat as much as one sheep, Mr Clifford is in effect entertaining a substantial flock of sheep on his land for most the year, with no return.
The Canada goose is an imported species that has done rather too well. The first birds arrived in 1665, to enhance Charles II's collection of ornamental waterfowl. In time, other landowners began to ape the king and introduce birds of their own, but those early arrivals seem to have stayed where they were released, and there was no great increase in numbers.
During the present century, however, the story has been different. Numbers rose so fast that during the Fifties the Wildfowl Trust caught and shifted at least 700 birds, to take the pressure off crops in hard-hit areas, and the Wildfowlers' Association of Great Britain and Ireland moved at least another thousand. Today the national population is estimated at more than 60,000, but it is rising at 8 per cent a year and threatens to double by the end of the millennium.
The sheer weight of geese, and the mess they create, cause consternation not only to farmers, but also to keepers of urban parks, where droppings are regarded as a public health hazard. It is estimated that wildfowlers shoot at least 15,000 Canadas a year, but this cull is making no impact on the population.
Various other methods of control have been suggested, among them poisoning, contraception, the pricking of eggs to prevent them hatching, or the destruction of safe nesting habitat such as islands; but none of these is either very attractive or efficient, and any attempt at control tends to lead to public outcry.
It seems sad that such splendid birds should arouse so much ill feeling. Ours, by now, were on the alert, heads up. In the far distance we could see the other half of our catching team advancing towards us.
The geese began marching towards the lake with the idea of launching themselves to safety . . . only to find that they had been outflanked by John Leadbeater, head of the local carp-fishing syndicate, who had put out in a powered dinghy with the express purpose of driving swimmers back to land.
Now was our moment: we popped out of hiding, advanced quickly along the bank in single file, then fanned out to make a line. Caught between two advancing armies, the geese stumped obligingly into the funnel and up into the corral. A few barnacles - 'Barnies' to the volunteers - still had the use of their wings and took off ahead of the waddling horde, but the great mass of Canadas was safely trapped.
The survey team moved quickly into action. Nigel, an expert, picked up one goose at a time, checked its sex and age, and passed it to a volunteer, who carried it under one arm down a line of checkers.
At the first station each bird was fitted with a metal ring bearing a serial number on one leg, and on the other leg a brightly coloured plastic ring bearing letters that can be read from a distance.
Next, each had two careful measurements taken: one of the length of the tarsus leg bone, the other of the distance from tip of beak to back of head. Then came a measurement of primary wing feathers, and finally each bird was gently lowered into a sack to be weighed. Tellers sat at tables, recording the figures.
Most of the captives maintained a stoical indifference to all this handling, but one or two big ganders launched assaults on their captors, biting vigorously at any part in reach, usually the backside, and every now and then one scored a moral triumph by shooting a load of slimy green droppings down its holder's trousers. Then, one by one, they were returned to the water, and set off honking for the safety of the deep.
What will such meticulous weighing and marking and measuring achieve? This is the fourth and final year of a study being conducted by the Wildfowl Trust and the data, once analysed, will certainly increase understanding of what makes Canada geese tick.
During the round-up your correspondent, goaded by his hunter-gatherer instincts, could not help thinking that it would be extremely simple to carry out a swift and effective cull by knocking every bird, or at least every other bird, on the head - and, indeed, massacres of flightless geese have been suggested as a drastic means of bringing numbers down.
It was, I suppose, a classic instance of how the interests of shooting men overlap with those of scientists: everybody wants Canadas to survive, but not to become such a menace that more and more people hate them.Reuse content