He then crossed the river and parked in the middle of a colony of nesting gulls, which numbered about 10,000 according to the Department of Conservation.
Police who received a complaint from a passerby observed Townhill's vehicle parked in the colony and a large number of distressed birds flying around it.
When attempts to signal Townhill to come to them failed, a police officer was forced to cross the channel on foot to speak to him.
Townhill denied knowing the birds were protected, and said the vehicle belonged to a mate who was fishing further down the river.
He eventually moved the vehicle, causing further destruction as he did so.
The officers were unable to estimate the number of nests and eggs destroyed, but noted the vehicle had been driven straight into the centre of the colony and back out again.
Townhill's lawyer Paul Bradford said his client had been staying with friends and had decided the give them some space and spend the night in his vehicle.
He claimed not to have seen warning signs and denied knowing the gulls were protected. He said he drove toward the birds without seeing the nests.
However, Judge Joanna Maze said it would have been obvious the birds were distressed.
She said the offence occurred at a time when there was still sufficient light to observe the birds circling his vehicle and calling in distress.