Birdcage Walk runs along the south side of St James's Park. The name comes from an aviary built there by James I.
St James's Park is the oldest of London's Royal Parks; it started life as the deer park for St James's Palace. In the 17th century, Charles II had it converted into a landscaped garden. George IV had it further landscaped in the 19th century. The lake in the middle of the park is a wildlife sanctuary with swans, ducks, geese, and even pelicans.