Downturn
It's rolling: The current sixth major extinction wave in Earth's history is taking its toll on the planet's animals and plants at a rapid pace. And their extent might even be underestimated - at least in the bird world. But there are also signs of hope.
For Anwarrudin Choudhury, it was certainly the biggest day of his ornithological life so far: June 6, 2006, when he made a sensational discovery. For the first time in more than seventy years without any credible evidence, Choudhury observed a Manipur bush quail (Perdicula manipurensis) during a field trip to Manas National Park in northeastern India.
This small gallinaceous bird lived in small groups in the vast high grasslands and swamps of Assam and was first scientifically described in 1905. After 1932, however, there were no more confirmed sightings of the bushquail-their habitat was largely drained and converted to cattle pasture or paddy fields to feed the state's rapidly growing population. As a result, experts questioned the continued survival of the species and began to consider adding the Manipur bush quail to the list of extinct species.
This would have placed the species in the sad series that has officially included 129 bird species since the beginning of modern times in 1500: from the famous Dodo of Mauritius at the end of the 17th century to the Po'o-uli (Melamprosops phaeosoma) from Hawaii, whose probably last representative died in captivity in November 2004.
Possibly the number 129 is also a drastic underestimation and in truth at least four times as many bird species have disappeared from the planet over the last 400 years as previously assumed. And if mankind does not take countermeasures soon, this trend could intensify again by the end of the century, researchers led by Stuart Pimm from Duke University in Durham warn in a new study [1].
So the majority of those feathered Pacific Islanders who fell victim to the expansionist efforts of the Polynesians after 1500, but long before the arrival of the Europeans, are missing from the official records: finds of historical, so-called subfossil bones from the last centuries indicate assume that up to a thousand different species of rail, pigeon or parrot could have fallen victim to the hunger of the new human arrivals, their animal companions such as pigs and rats or to clearing. During this time, Hawaii alone lost up to 60 percent of its almost 140 endemic bird species and New Zealand half - according to the researchers, the same applies to the islands of other oceans.
In addition, there are many species that are known to science not only through their skeleton, but at least through their skin or even research work, but have long been classified as missing. These include the hooded mermaid (Sporophila melanops) from Brazil - lost since 1823 - or the Oloma'o thrush (Myadestes lanaiensis) from the Hawaiian Islands, which was last seen in 1980. For various reasons, ornithologists declare them as extremely endangered, but not yet officially extinct, because intact habitats still exist in the original range or because the birds are difficult to observe because of their ste althy way of life.
Now Stuart Butchart of the conservation organization Birdlife International and his colleagues have taken the trouble to comb through this list of shaky candidates for species that may actually have disappeared forever [2]. According to her research, another 14 bird species have died out, while the Spix's Macaw (Cyanopsitta spixii) survives today only in human captivity. Pimm's team also included these animals in their calculations.
The bone finds like these more recent losses could still only be the tip of the iceberg, the researchers fear based on statistical calculations. This is because most skeletal relics come from the group of non-songbirds, which are larger and heavier, making their remains more enduring than those of small passerine birds. However, their number of species is twice as large, so high losses in the group of songbirds must also be feared.
In addition, the extinction naturally affects rather rare species with small distribution areas, such as are often found in tropical forests and mountains. Some areas such as the Mata Atlantica - the coastal rainforest of Brazil -, the Andes or West Africa have already lost huge areas of their natural vegetation in historical times, so that it is very likely for biologists that many bird species were lost before they were scientifically recorded.
All in all, Pimm and Butchart and her colleagues calculate that at least one bird species has been going extinct every year since 1500, which is 100 times faster than the natural rate of extinction. And with about a quarter of the 10,000 known species currently endangered, that rate could increase tenfold by the end of the century-unless the current adverse conditions change.
The reasons for biodiversity decline are well known: First is the rapid conversion of natural to cultivated landscapes, followed by excessive hunting and introduced exotic animals. Climate change is also likely to gain in importance in the future, as it shifts vegetation zones and thus endangers entire ecosystems.
A study by Niclas Jonzén from the Swedish University in Lund offers a glimmer of hope, at least for European migratory birds [3]: The long-distance migrants are probably reacting more flexibly to global warming than previously forecast, as they now leave their African winter vacation earlier return to the breeding areas and thus be able to provide their chicks with the insect stocks, which also start earlier.
And Pimm's team also offers good news at the end: Over the past three decades, the global extinction rate has fallen again slightly, because intensive conservation measures have saved at least 25 species from an otherwise certain species extinction. Conservation can really pay off.
