Ice ages explain decline in avian biodiversity

By studying bird species, scientists have discovered that major decline in biodiversity coincides with ice ages rather than human activities. Researchers at Uppsala University’s Evolutionary Biology Centre used mathematical calculations and found that a major fall in bird species occurred during ice age periods 2.5 million years to 11,500 years ago.

Hans Ellegren, Professor in Evolutionary Biology, said: “The majority of all species exhibit cyclical swings in numbers and these swings often coincide with the periods of ice ages”.

In the study, published in Current Biology, the team analysed whole genomes and the genetic variation of DNA molecules of 38 bird species from 1–10 million years ago up until about 10 thousand years ago. By calculating how many individuals of each species have existed during different time periods, the scientists estimated today’s genetic variation.

The results showed that species variation is dependent on climate change where population sizes varied by at least three orders of magnitude among bird species during the Quaternary period (2.5 million years to 11,500 years ago). The team also found that decline in species distribution occurred during the Pleistocene Epoch – 11,500 years ago – when inland ice spread across Earth.

“The last Ice Age (110,000-12,000 years ago) had a particularly heavy impact on birds. Many species suffered their most dramatic falls in numbers then,” said Professor Ellegren.

The researchers also studied threatened species such as the crested ibis and the crowned crane and discovered that these species began to decline before anthropogenic activities affected them.

“We’ve analysed several species classified as “endangered” in the IUCN Red List of Threatened Species. Several, such as the crested ibis, crowned crane, brown mesite and kea, were already at a low level even before human activities affected their ranges,” added Professor Ellegren.