This article first appeared on iCatCare here and more about their work with unowned cats can be found here.
Feral and street cats cannot simply be picked up and taken to a veterinarian for neutering and they cannot be kept for long recovery periods in veterinary cages. They need to be treated to an extent as wild animals because they do not tolerate handling (and thus can be dangerous) and can find proximity to people highly distressing.
For feral and street cats the solution to population management is called Trap Neuter and Return (TNR). It is a widely implemented method of humane cat population management and is internationally recognised for managing non-pet cat populations by controlling their reproduction.
> Trap, Neuter, Return (TNR)
Useful resource:Humane Cat Population Management Guidance from the International Companion Animal Management Coalition