The migration each year of nearly 5 billion birds from breeding grounds in North America to wintering grounds in Central and South America and the Caribbean (the “Neotropics”) is both one of the wonders of nature and what marks the season for birders. Some of those birds even stay and overwinter here in Los Angeles and other southern reaches of North America. A Western Tanager stopped under our oak tree as this column was going to press but it will be another month before the Yellow-rumped Warblers arrive for the winter.