The tree trimmer at the center of a federal and state investigation into the destruction of nests and slaughter of baby birds in Oakland said Thursday that he "screwed up" because he allowed his crews to chain-saw trees even as baby birds were falling out. Pulido was the supervisor for a crew of tree trimmers hired Saturday by the U.S. Postal Service's Civic Center Annex in Oakland. The post office ordered trees containing the nests of egrets and black-crowned night herons, species protected by the U.S. Migratory Bird Act, to be cut because the nesting birds were defecating on mail...