Yellowhammer dialects from the introduced population in New Zealand has raised some new questions.
Last year we introduced readers of the BOU Blog to 'Yellowhammer Dialects-, a citizen science project aiming to identify if, when and how the different song dialects of Yellowhammers (see Figure 1) evolve and change after introduction to a new region. This time the focus will switch more to history.
It is often assumed that British birds such as House Sparrow, Blackbird and Yellowhammer were introduced to New Zealand by early European settlers for sentimental reasons to remind the colonisers of home. The principal motives behind many of these introductions however may have been somewhat different.
During the European settlement of New Zealand from 1840 onwards, great swathes of land were cleared of native forests to make areas suitable for grazing animals and arable cultivation. This caused a reduction in the native insectivorous bird populations. The knock-on effect of native bird population declines was a boom in the numbers of various insects, many of which could be crop pests. Because New Zealand had no native mammals that could take the place of the birds as the natural enemies of the insects, early settlers turned to non-native bird species to control the insect problem.
From the early 1860s onwards 'Acclimatisation Societies- were formed with the aim of transporting non-native species from Britain and Europe to New Zealand. Among the birds most desirable for introduction were several small passerine species, including the Yellowhammer. Yellowhammers were first introduced to Nelson in the South Island in 1863 and, despite complaints by farmers, Yellowhammer introductions in other regions continued until the late 1870s. Yellowhammers then spread across the country so rapidly that in less than 20 years their status changed from welcome guests to undesired pests. It wasn't long before the colonisers realised their mistake that the Yellowhammer, along with many of the other introduced bird species, are not in fact wholly insectivorous. Yellowhammers are predominantly seed-eaters who only prey on insects during their breeding season.
Overall, during the 1860s and 1870s more than 600 live Yellowhammers were shipped from London to New Zealand (Figure 2). More than half of the introductions can be traced via historical records to just one family, Richard Bills and his sons, who made a fortune from this business. In 1880 public opinion in the Canterbury region of the South Island changed swiftly against further Yellowhammer introductions. In Canterbury the voice against further Yellowhammer introductions was so strong that a consignment intended for release in the region were landed but instead of being let free, the birds were loaded on to another ship bound for Australia.
From the 1880s onwards the Yellowhammer was considered the farmer's foe in New Zealand and was even considered by some to be on a par with the number one pest, the House Sparrow, another introduced species from Europe. Around this time local bodies, and later the Provincial Government, initiated a large cull of non-native passerines. Although the culling effort was on a large scale, with hundreds of thousands of eggs collected by children and many birds shot, or killed by poisoned grain, each year, it had only a small effect on overall population levels of non-native bird species.
Today, New Zealand is still a paradise for many British bird species, where species such as the Yellowhammer are far more common than in Britain today. From their initial introduction to New Zealand, Yellowhammers have increased from several hundred individuals to probably several million (or more?) and then declined to the levels we see today (approximately two million pairs). Despite the Yellowhammer no longer being an object of hate for New Zealand farmers, the species is still regarded as a crop pest.
In our previous article we argued that because only a subset of the British population of Yellowhammers was introduced to New Zealand at the time, it is reasonable to expect that only a subset of the British song dialects were transported and the rest 'missed the boat-. However, our preliminary results contradict this prediction. Over the past year we have collected over a hundred recordings of Yellowhammer song from locations across New Zealand and 150 from across Britain. We were able to add these New Zealand and British recordings to a library of earlier recordings from across the Czech Republic and compare dialects in New Zealand with those from across a wide area of Europe. Although we had fewer recordings from New Zealand than we did from Britain, we identified more dialects from our New Zealand recordings than the British ones (Figure 3). Intriguingly, we found that the four dialects missing from the British samples were present among European Yellowhammer populations.
These findings raise many new questions. Were these 'missing' dialects present in the British Yellowhammer population in the past and disappeared due to recent rapid population decline? Or are the dialects still there but we have failed to sample widely enough to identify them? Is Britain the sole origin of the Yellowhammers that were introduced to New Zealand up to 1880?
You can help us answer these questions by getting involved in the project at yellowhammers.net. All you need is a digital camera or mobile phone and enthusiasm! We are especially interested in recordings from a broad area around Brighton because we think it's likely that all Yellowhammers liberated in Otago and some of those liberated in Canterbury were caught in this area. Brighton was the base of Richard Bills and his business in animal transportation. We have evidence that on at least one occasion he collected birds around the city and travelled with them to London and then to New Zealand.
Please visit yellowhammers.net for more information on the project and how to get involved.