A novel/book from the 90's. Society used genetically modified animals to perform basic tasks. For example, birds were genetically modified to be large enough to carry passengers like our passenger jets. I believe the police used modified falcons or some other bird-of-prey (important to the story) as their transports. Turtles (I think) were modified and used as buses, though smaller things were also used for POVspersonal vehicles. I don't remember how they were used other than for transportation.
The story was a mystery where the main character was a police detective, investigating a recent string of events where some of the animals were suddenly reverting back to their base natures and killing people and hurting other bioengineered animals. The investigation inevitably started with the primary bioengineering lab where these animals were created, but beyond that, I don't recall.
It was an intelligent book of about 400 pages. I had a paperback copy, on which I think the cover showed a police bird-of-prey transport flying over the city.
