sentences:  Birds such as the aforementioned piculet are specialized for gleaning the bark of trees, as are nuthatches, woodcreepers, and treecreepers.Most bark-gleaners work their way up tree trunks or along branches, though nuthatches are well known as the birds that can go the opposite direction, facing down and working their way down the trunk, as well.This requires strong legs and feet on the part of the nuthatch and piculet, while birds that face upwards tend to have stiff tail feathers to prop them up.