''He did not stop due to having his son in the vehicle, who would have been upset at what had occurred.''
She could not say if police intended to take action against the man.
SPCA Otago director of animal welfare Dr Helen Beattie said in any case of ill treatment of an animal, the Animal Welfare Act contained penalties ranging from a fine to up to five years in prison.
A successful prosecution relied on an admission of guilt, or evidence that established beyond a reasonable doubt that animals had been harmed as the result of a ''purposeful, knowing act''.
Dr Beattie said such incidents were ''not common at all'' in the SPCA's experience.
On the contrary, its staff rescued many ducklings at this time of year as a result of calls from the public.
''Mother ducks are not necessarily very smart about where they get their broods to hang out.''
She urged motorists to show patience if they encountered ducks and other birdlife on the road.
''It's going to cost you two minutes of your day to let them walk across the road.
''I would say the same thing about passing a cyclist - just be patient.
''At the end of the day you get one shot at this world. You want to be a nice person - do the right thing.''