Yellowhammers: Hero to Invasive Villain in 15 Years

This is a map of New Zealand identifying the locations of the principal Regional Acclimatisation Societies.
Image Credit: Pavel Pipek

Introducing foreign species into new regions has long been fraught with problems but researchers have found a way to track some of the long-term consequences of the establishment of a new species.

A study published recently in Neobiota uses 19^th century newspapers and documents to track the introduction of the yellowhammer (Emberiza citrinella) from regions around Brighton, England to New Zealand.

As part of the study, researchers found that the bird was initially brought in in the mid-19^th century to try to bring pest insects under control after many of the native New Zealand birds were eliminated with the clearing of forests. However, public perception turned against the yellowhammers over a course of 15 years as people realized the birds fed predominantly on valuable seeds rather than insects like caterpillars and black field crickets.

This image shows the number of imports and liberations of yellowhammers in the Auckland region in 1871 (likely scenario).
Image Credit: Pavel Pipek

The researchers dug through data that included nearly precise information about the number of birds released through shipments and where exactly they were released during the 1860s and 1870s. But the last shipment of yellowhammers that arrived in 1880 was never released as public pressure forced the so-called Acclimatisation Society that was created for the purpose of introducing new animals and plant species to the islands of New Zealand to get rid of the birds.

The yellowhammer was subsequently the target of hunting, egg-collection and poisoning, but none of it was successful in removing the established bird from New Zealand and they remain part of the fauna today.

Authors of the study said that this kind of detective work can show us some of the ways that some species are successful in establishing populations in new regions and could points possible ways to stop new harmful invaders from spreading.