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The methods used by exasperated zoo-keepers included trying to dazzle the bird with a fire brigade searchlight before nabbing him when he was distracted.

"We have searchlights on all night to try to see ice - it can come from nowhere," he explains.

The task is a bit like discerning a field of fireflies around a central, massive searchlight.

They inched along, careful to avoid the beams from the guards' searchlights.

They moved like a desperate parade — carrying lunch bags and borrowed tools — into the glare of searchlights, guard dogs and barricades.