鲍鱼tv

Pine trees enclose their seeds in cones for protection. When the cones are green, the seeds within are quite beyond the reach of most birds but the crossbill has special equipment. It is the only finch that can twist its upper and lower bill in opposite directions, enabling it to lever open the pine cone and reach the seed within. After a meal of pine seeds, some American crossbills will regularly fly off to a bank of exposed clay which they eat to aid digestion. Green pine cones are very resinous and may cause stomach upsets. Clay in the stomach may absorb the resin and prevent any trouble.