IIRC the issue with waterfowl conversion was sudden failure of seals, buoyancy and ballast systems.

The seagull program was hit with the extra problems of salt water

Last leak mentioned the advances have made in the house sparrow model, but battery life is still an issue.

Songbirds aren't used due to birdwatchers; as outlined in the paper "Avain surveillance: security, counter surveillance, and camouflage" read the updated 2019 version.