The apple hit one of the ducks, knocking it unconscious.
He then picked the animal up, taking it behind a nearby rubbish bin where he stomped and kicked it until it was dead. He then disposed of the carcass in the bin.
The 26-year-old, who appeared over audio-visual link before Judge Andrew Nicols, is serving a significant prison term of 14 years for previous offending.
He was sentenced in 2016 after he assaulted a prison guard, punching him and knocking him unconscious against his cell bed frame, causing a concussion and cuts to the head.
Judge Nichols said today that the attack on the winged victim was "a dumb thing to do" but that the court's time was precious, and they were spending more time on the case than it was worth.
"This should not have happened Mr Sanders, this was a dumb thing to do."
Defence lawyer Matthew Crooymans asked for his client to be sentenced to a prison term concurrent with his current lengthy sentence.
Crooymans did not offer an explanation for his client's behaviour, who has an extensive history of violent offending.
Judge Nichols agreed and Sanders will continue to serve his 14-year sentence "working on himself".