Pest control gone awry

The yellowhammer (Emberiza citrinella) was introduced to New Zealand in the late 1800s to combat insect pests of settlers’ crops. Spotted the major flaw in this plan? Yellowhammers are primarily seed eaters, not insect eaters, although this was not well known at the time the yellowhammer was selected for acclimatisation. They liked New Zealand’s cereal crops, a fact that so alarmed farmers that the final shipment of yellowhammers was stopped from disembarking and instead sent on to Australia. Despite subsequent poisoning, egg stealing and shooting efforts, yellowhammers have spread throughout New Zealand.