New Zealand's Beech Forests Are Missing Their Giant Birds

This Cortinarius porphyroideus is one of many New Zealand mushrooms that evolved to resemble fruit to attract the attention of birds that are now extinct, or very nearly so. PNAS 

 

It's been six centuries since New Zealand's giant moas were wiped out by a double punch of humans and imported rats. However, a study of coprolites, or fossilized dung, suggests the effects have yet to fully ripple through the ecosystem, and the absence of avian spore dispersers could spell danger for the islands' beech forests.

Dr Jamie Wood of New Zealand's Landcare Research went hunting for coprolites left behind by moas, some of the largest birds that ever lived, and kakapos, the near-extinct world's largest parrot. “Coprolites were actually more common than we’d thought, once we started looking for them,” Wood said in a statement. “And it turns out they contain a huge range of important information about past ecosystems.”

The ancient dung confirms both birds ate a lot of leaves, ferns, and mosses, but also more fungi than people had realized, Wood reports in Proceedings of the National Academy of Sciences. The discovery explains New Zealand's array of brightly colored mushrooms. Whereas in some parts of the world toadstools develop their colors to warn against eating them, in New Zealand it seems the colors were advertising to moas and kakapos in the hope they would become dispersal agents for their spores.

A moa coprolite in the sediment that buried and preserved it. Dart River Valley, New Zealand. PNAS

Unfortunately for the mushrooms, when humans brought rats and possums, the mammalian intestines proved much harsher on the spores. Without bird assistance, mushrooms can maintain their presence where they are established, but can't reach new territories.

Co-author Professor Alan Cooper of the University of Adelaide explained to IFLScience this has wider implications, as the beech forests that represent half of New Zealand's tree canopy depend on a symbiotic relationship with the local mushrooms. Cooper added the moa's role explains the presence of “beech gaps, where people have been puzzled why forests have not recovered.”

The problem is likely to grow as the world warms. Increasingly, forests need to move to higher altitudes to hold onto familiar climates, but Cooper said the mushrooms now find it particularly difficult to send seeds uphill, something moas could have taken in their gigantic strides.

New Zealand still has a rich bird life, but Cooper said most non-carnivores are too small to chew through the mushroom caps. Cooper doesn't think the return of kakapos to the mainland will be realistic soon. However, he said the discovery that mushrooms were once so important in their diet may help with the longstanding problem of getting them to breed (with each other, rather than passing biologists). 

The coprolite analysis also reveals the moas had many intestinal parasites. Some of these were shared with waterfowl, but others died out when the moas did. Cooper acknowledged the difficulty in making people regret the loss of biodiversity these parasite extinctions represent.

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