Will Sikaflex Concrete Fix harm birds if it is used to repair cracks in a concrete bird bath?

No, Sikalfex Concrete Fix will not harm animals after a full cure. Please allow for a 5 to 7 day cure before submitting the sealant to service. The cracks must be a minimum of 1/4” x 1/4". Sikaflex Concrete Fix remains flexible to allow for movement. It cures to a hard rubber.