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Reply to Pamela Wade: Dawn chorus could do with some imported performers

There is a standard joke in the UK that when you visit New Zealand you have to set your watch back 30 years. That would still put you 100 years ahead of Pamela Wade though, judging from the views expressed in her article in Wednesday's Herald. Ms Wade bemoans the poor quality of the native songbirds, which she compares unfavourably to the "heart-lifting glory" of the exotic species introduced by the "pioneers in the 19th century - people who have since been vilified for their insensitivity to biological purity". When gardeners can augment their beds with the best that other countries have to offer, why, she asks, should we not be able similarly to enhance our parks and gardens with pretty and tuneful birds from around the world? Perhaps Ms Wade has taken to heart the conservation message that 'biodiversity is good' and thinks that releasing yet more exotics would enhance New Zealand's backyards - but her views are at best silly and outdated, and at worst downright irresponsible.

If the local dawn chorus is so lacking, we wonder if Ms Wade has asked herself why? One reason could be that so many of the original indigenous songbirds have been driven extinct. What the locals woke up to 250 years ago, before the "pioneers of the 19th century", we will never know. We can gain some clues, however, from the writings of the early explorers. It was said that as Captain Cook sailed up the coast of New Zealand, the noise of bird song from the forests was deafening. Quantity does not imply quality, of course, but clearly the chorus that greets the dawn today is greatly depleted of native singers.

Ms Wade might also consider why so many native bird species have gone extinct. In almost every case the answer is the effect of exotic species - species that have been introduced to New Zealand by the hand of humanity. The worst of these exotic invaders is humanity itself, which has hunted its way through moa, adzebills, rails, and ducks, species that were once found nowhere else in the world, and are now just found nowhere. Humans like to hunt large, meaty animals, but it is the small songbirds that are the main contributors to dawn choruses around the world. These have suffered just as badly since humans reached New Zealand, thanks to the combined efforts of rats, cats, stoats, ferrets, weasels, possums and hedgehogs. No one will now walk their dogs to the sound of piopio or huia, or any of the 8 species of songbird that we know fell extinct before Ms Wade was born. Worldwide, exotic species have been responsible for literally thousands of bird extinctions.

Of course, Ms Wade is not advocating the introduction of mammalian predators, and we must be grateful for small mercies. But species are not just eaten to extinction. Natives can be out-competed by exotics. In autumn, flocks of starlings that strip kahikatea of their fruit deprive native species of an important winter food source. Exotics may bring diseases to which the natives have no immunity. Avian malaria carried to the Hawaiian Islands in the blood of introduced birds means that most native songbirds, which have no natural immunity, are now restricted just to the high altitudes that the mosquito vectors of the disease cannot tolerate. Perhaps the budgies that Ms Wade is so keen to see brightening her garden will bring the disease that finally finishes off the kakapo, or will eat kakariki out of house and home? Maybe not, but what Ms Wade is advocating is effectively to play a game of Russian roulette with her national heritage. Indeed, with global heritage, for while exotic species may raise local diversity, their effects on unique and distinctive biotas such as that of New Zealand decrease the diversity of the world as a whole.

Ms Wade's analogy with garden plants is also poorly chosen. As the Department of Conservation fights battles against gorse, broom and pine, who can say which of the species in her garden will spread to become New Zealand's kudzu or prickly pear? Controlling exotic pests already costs the global economy billions of dollars a year. It is with good reason that the customs service operates such strict controls on what is imported into this country - once the can is open, it is difficult to get the worms back in. Why should birds get special treatment? Local farmers would not be too delighted when flocks of the exotics whose virtues she extols descend on their crops, as starlings, sparrows and finches already do.

Finally, even if we put side logic and common sense, we still see no merit in Ms Wade's arguments. They are based solely on her preference for some sounds over others. As scientists, we love the music that the tui produces, and know researchers who can tell individual males apart by their unique songs. We could likewise contrast the beauty of the bellbird, fantail, and grey warbler with the asthmatic wheeze of the yellowhammer, or the monotonous chip of the house sparrow, but that would be as pointless as to argue for the primacy of Bach over Mozart. The songs of all these species are beautiful, and a failure to find them so is more indicative of a deficiency in the ear of the beholder than in the voice of the singer. Moreover, these singers and the chorus they produce are found in only one place in the world. People come to New Zealand to experience the unique and beautiful environment here, and that includes special creatures like the tui. To find blackbirds and chaffinches in the forests is as appealing as finding a branch of McDonalds tacked on to the Taj Mahal. We suggest that Ms Wade moves on from 19th century attitudes to the introduction of exotics, whose realisation has irreparably blighted these magical islands, and instead celebrates all that is distinctive about New Zealand. That would be better than arguing for the creation of an ecological Frankenstein's monster.

Dr Tim Blackburn and Phill Cassey

Dr Tim Blackburn and Phill Cassey are both scientists studying biological invasions, extinctions and the relationship between the two.