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Birds New Zealand national president Bruce McKinlay, of Dunedin, said white-faced herons were the most common heron in New Zealand and made use of a range of habitats.
Mr McKinlay had heard reports of herons investigating their reflection.
"In this case it could be that the birds can see themselves or ‘another heron’ in the windscreen and are checking it out," he said of the heron photo, taken on Sunday.
Otago Harbour provided very good habitats for white-faced heron as the harbour was sheltered and there were many "indented shorelines to forage along".
"As well there are a lot of large trees along the harbour which are good for herons to roost and nest in," Mr McKinlay said.
The birds had strong claws for walking in the mud and for hanging on to trees while roosting and nesting, but he had not heard of any cases of vehicles being damaged by herons.
There was no evidence that the white-faced heron population was rising in the harbour, he said.