Aggressive territorial behavior of wren in winter

At about 11.00 GMT on 27th December 1981, a cold, frosty morning with snow, near Littlebourne, the author saw three or four wrens Troglodytes troglodytes feeding beside one another near stones, concrete blocks and cut watercress where there was running water and consequent likely food. One wren was uttering loud and continued song. A few minutes later, during a snow shower, the authors watched two wrens, one a singing male, from about 12m. The singing one approached another, which was feeding, and tried to chase it off, while continuing to sing loudly; the latter merely flew and hopped under some blocks and timber, and proceeded to seek food. Following the fourth or fifth attempt to drive this second wren off, the singing male pounced upon it, wedged its body against a stone, holding it down with one foot, and started controlled, powerful pecking, with a rhythmic hammering action.