In Oregon, dogs and cats are considered personal property. It is theft of personal property when you “take, appropriate, obtain or withhold such property from an owner.” (ORS 164-015). So, while it is legal to trap a cat on your property, it may be construed as theft if you knowingly take property from an owner.
When people bring us a roaming animal that freely comes up to them or one they trapped, and provide us with the information we request on where and when the animal was found then that person has met their obligation.
Cats brought to Willamette Humane Society in a live-release trap are scanned for microchips if surrendered to the shelter, but not before spay & neuter surgery in the clinic.