They may look innocent enough, but these sparrows are anything but.

"They're little thieves, but they're interesting little thieves," Clare Browne says.

She's part of a study into these bizarre sugar thefts by behavioural animal researchers at Waikato University.

"We're quite interested in just what the birds do. Are there just some birds which are stealing more than others? Is it just the males? is it males and females? Are the parents perhaps teaching their offspring?" Browne said.

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"It's quite novel foraging behaviour and it shows that these birds are able to adapt to living in a human-modified environment which is quite important to their survival."

Every morning when the cafe opens at 7am Michael Davy is there for his daily bird watching.

He said the sparrows steal almost as soon as the tables are set and the condiments put outside.

"They'll land on the cup, they'll pull one out or maybe they'll pull two out sometimes, then they'll peck the ends until its open, they'll grab it in the middle of the sugar packet and they'll shake their head. Sugar will come out and they'll peck around it," Davy said.

The study has found that if there's too much competition from other birds, the sparrows will take their haul elsewhere. Mike has found hundreds of stolen sugar packets right across campus.

"They distribute the sugar packets within a 1km radius of the café," Davy said.

Over a course of a year, Mike estimates these thieving birds could cost the cafe up to a thousand dollars.

Cafe staff say 2017 has been the worst year for sparrows stealing sugar.

They also seem to have a preference for brown sugar in orange packets.

"They only go for the raw sugar because the grains are much larger and they can actually pick it up," Davy said.

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