To ensure that Western Shield is working effectively, how native animal populations are responding to the reduction of predator numbers needs to be measured.
The department monitors animal populations at selected sites within baited areas in various ways, usually by trapping (and releasing) the animals that need to be monitored.
Western Shield's monitoring shows that the baiting of foxes and feral cats is having a positive effect on the State's native animals.
The success of Western Shield and previous programs has resulted in the removal of the 
woylie, tammar wallaby and quenda from Western Australia's threatened species list.
Unfortunately, monitoring since 2001 showed an unexpected and rapid decline in the population of woylies across the south west of Western Australia.
The woylie is now re-listed as threatened, and the department is conducting research to see why numbers are falling and to aid in the recovery of the species.
Monitoring and evaluation also means that Western Shield can be regularly reviewed to make it even more effective by: