The works, featuring swallows, were made by Shrewsbury artist Matt Sewell for the town's Belle Vue Arts Festival. They have gone from Greyfriar's Bridge.
A festival spokeswoman said: "Our much-loved swallow art pieces, created by local artist Matt Sewell, are missing. They were in place on the railings by Greyfriar's Bridge as part of the festival on Saturday, July 24, but seem to have flown the nest by Sunday morning.
"If you have any information that would be helpful in locating them, then please don't hesitate to get in touch. You can email us on email@example.com"
The festival has been a popular annual event in Belle Vue, and was extended this year to give more people the chance to enjoy it while obeying Covid-19 regulations.
Children's drawings, colourful bunting and artistic scarecrows have been put up, and a range of creative activities have taken place.