In a churchyard at night at the 2015 (best guess) Durham Lumiere (Durham City, Co. Durham) many trees had 'birdboxes' outlined in neon tube up the tree though no actual box, its dark remember. Birdsong came from a speaker hidden by each birdbox, each one different so at night the multitude of birds could be heard as you walked about.
But they weren't birds; all the 'birdsong' had been sung by a choir!