If BBC is actually about the covert 'natural' hijacking of urban street furniture...

...and not really about birds, we might want to consider some other creatures.

Butterfly houses (although there's no evidence that butterflies use them)


Ladybird houses


Bee houses


Bat houses


Maybe one day we can aspire to this sort of scale (with urban integration of course). This is one of the loveliest things I have ever seen

1914. Dr. Charles Campbell and a "municipal bat-roost" in San Antonio, Texas ("for one of man's best friends"), his idea for mosquito control at a time when malaria was a major public health problem in the U.S. Disguised as a favorite bat habitat — a church steeple, complete with cross — the roost was fitted with a trapdoor and stilts to facilitate the harvesting of guano by the wagonload for use as fertilizer. 5x7 glass negative, George Grantham Bain Collection.

From here