A higher manification lens reduces the plane of focus also called the depth of field (i.e. the area of the picture that is in focus). A higher f stop increases the plane of focus.To get several birds in the tree in focus, try using a higher f stop, like f/11, or f/16 or even higher and use the lowest magnification on your lens that will still work for the photo. You could possibly use a little less maginficaiton and crop the image.
