Attrition is the reduction, over time, in the number of community cats that have been TNVR'd (trap-neuter-vaccinate-return) and living in managed colonies. TNVR includes spay/neuter/vaccinate and return to the territory where the community cat was originally humanely trapped.
Since no reproduction occurs after TNVR, the population is stabilized. Attrition then occurs due to the process of aging, predator animals, and in some cases, humane and human intervention. This creates the conditions for the community cats to die off, thereby reducing the numbers in any one managed colony.