CLIMATE CHANGE DISRUPTS SONGBIRD’S TIMING WITHOUT IMPACTING POPULATION SIZE (YET)
Songbird populations can handle far more disrupting climate change than expected. Density-dependent processes are buying them time for their battle. But without (slow) evolutionary rescue it will not save them in the end, says an international team of scientists led by the Netherlands Institute of Ecology (NIOO-KNAW) in Science this week.
Yes, spring started late this year in North-western Europe. But the general trend of the four last decades is still a rapidly advancing spring. The seasonal timing of trees and insects advance too, but songbirds like Parus major, or the great tit, lag behind. Yet without an accompanying decline in population numbers, it seems, as the international research team shows for the great tit population in the Dutch National Park the Hoge Veluwe.
“It’s a real paradox,” explain Dr Tom Reed and Prof Marcel Visser of the Netherlands Institute of Ecology. “Due to the changing climate of the past decades the egg laying dates of Parus major have become increasingly mismatched with the timing of the main food source for its chicks: caterpillars. The seasonal timing of the food peak has advanced over twice as fast as that of the birds and the reproductive output is reduced. Still, the population numbers do not go down.” On the short term, that is, as Reed, Visser and colleagues from Norway, the USA, and France have now calculated using almost 40 years of data from this songbird.
This is the first time that density dependence – a widespread phenomenon in nature – and ecological mismatch are linked, and it is a real eye-opener. Reed: “It all seems so obvious once you’ve calculated this, but people were almost sure that mistiming would lead to a direct population decline.”
The mismatch between egg laying period and caterpillar peak in the woods will keep growing, and so will the impact following the temporary rescue, as long as spring temperatures continue to increase. “The density dependence is only buying the birds time, hopefully for evolutionary adaptation to dig in before population numbers are substantially affected,” according to Visser. The new findings can help to predict the impact of future environmental change on other wild populations and to identify relevant measures to take. Even rubber bands stretch only so far before they break.
With more than 200 staff and students, NIOO is one of the largest research institutes of the Royal Netherlands Academy of Arts and Sciences (KNAW). It specialises in terrestrial and freshwater ecology. As from 2011 it is located in a sustainable research building in Wageningen.
Article: Population growth in a wild bird is buffered against phenological mismatch. Thomas E. Reed, Vidar Grøtan, Stephanie Jenouvrier, Bernt-Erik Sæther & Marcel Visser, Science, 26 April 2013.
More information, including a copy of the paper, via the AAAS Office of Public Programs: +1-202-326-6440, email@example.com
Pictures are available. See a.o. the downloads here below. Source: NIOO-KNAW.
Follow us on Twitter: @niooknaw