Tau has been on leave from his role as runanga chairman since last October. He had also resigned as chairman of Tuhoronuku, the Ngapuhi group with a controversial mandate to negotiate a Treaty settlement with the Crown.
After yesterday's hearing Tau apologised for killing the birds and said his goal now was to contribute back to the community.
Pita Tipene, co-chairman of Te Kotahitanga, had previously called for Mr Tau to stand down from the chairman position.
Te Kotahitanga have long opposed the Tuhoronuku mandate, saying it lacks support from most Ngapuhi and ignored many concerns that needed to be heard before settlement can proceed.
Mr Tipene said Ngapuhi had moved on from the time when Mr Tau headed Tuhoronuku.
"Sonny Tau began the settlement process but it's time for new leadership," Mr Tipene said. "I think he was already gone and we didn't need a conviction to see that."
Tau had pleaded not guilty to the perversion of justice charge but after a sentencing indication hearing before Judge Mark Callaghan in the Invercargill District Court yesterday, he changed his plea to guilty. Tau had already admitted hunting and possessing the kereru.
Judge Callaghan indicated Tau would be fined $12,000 on all charges, ordered to pay $12,500 in costs to DOC, sentenced to three months' community detention and ordered to undertake 100 hours of community work. Community detention allows an offender to work but restricts them to their home address during specified curfew periods.
Tau was convicted on the charge and remanded to appear for final sentencing on all three charges on June 16. Sentencing will be via audio visual link from Auckland District Court.
Judge Callaghan said Tau changed his story not long after he was initially interviewed and charged. He told DOC Sadlier had shot the birds near Otautau but he (Tau) had accepted responsibility to protect his daughter, Sadlier and their children. In November, Sadlier was convicted of obstructing the course of justice by agreeing to make a false statement and was ordered to pay a $1000 emotional harm payment to DOC.