Yellow Warbler For years while having a coffee I have been watching Yellow Warblers foraging in the lonely Birch tree in front yard. They seem to prefer the Birch over all the pines. I am so use to seeing them that the piece may have never been expect l I happen upon a Yellow Warbler study skin. Studying the skin opened my eyes to what little gem they were. The Alter tree is a member of the birch family but unlike the birch the male catkins flower before the branch buds. The contrast between the flowering male and bark female catkins is like the changing of the seasons. New growth verse old growth, spring verse winter.