The Society for the Prevention of Cruelty to Animals was investigating the deaths of 50 peacocks in Rolling Hills Estates since 2012.
Some of the birds have been discovered shot or poisoned.
Peacocks were first brought to the area in the 1920s.
Since then the population has grown considerably and the ASPCA suspects someone became fed up with their presence and took matters into their own hands.
Killing a peacock is a crime in California punishable by prison and or a $20,000 fine.
Investigators were asking anyone with information to come forward.