How Yellowhammers Went from Heroes to Zeros

Scientists trying to reconstruct the history of yellowhammers in New Zealand show how these small, colorful and seemingly innocent birds went from heroes to zeros in just a matter of 15 years.

Yellowhammers, hailing from Europe, were first brought over to New Zealand during the 19^th century as a way to help fight insect crop pests, then not knowing that these birds would become pests themselves.

In a new study published in the open access journal NeoBiota, researchers used newspaper articles from 19th century as well as original documents kept by Acclimatization Societies - organizations founded specifically to introduce new animals and plants to New Zealand - to follow the trail of the yellowhammer from Europe to New Zealand.

What they found was that while New Zealanders - also called Kiwis - were settling down and populations were fast growing, so were insect crop pests like caterpillars and black field crickets. Normally insectivorous birds would be used to control these nuisances, but because the settlers had cleared away forests and all the native birds that lived in them, there were no birds around to fill this role.

That's when the yellowhammer came to the rescue. Acclimatization Societies at the time thought the yellowhammer was up to the task, and so chose to ship these heavy-billed birds over to New Zealand to take care of the pesky pests. But these heroes, so to speak, soon became public enemy number one, because as it turned out, their diet mainly consisted of seeds and the very cereal crops they were brought in to protect, and not the crop pests.

Despite all efforts to rid the country of yellowhammers, via target shooting, egg-collection and poisoning, it was too late, and until this day yellowhammers remain widespread across New Zealand.

The detective work by the scientists not only identified where the yellowhammers came from, but also the specific places where they ended up, showing that looking into the past can reveal a lot about a species.

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