Possible Clues:

• Birds as a class of vertebrates
• Birds' biological class
• Lex and Park, e.g., in N.Y.C.
• Old greetings
• Welcomes
• Fifth and Sixth, in N.Y.C.
• Mad. and Lex.
• Birds, in Latin
• Park and Lexington, e.g., in N.Y.C.
• Madison and Park, e.g. (Abbr.)