Migrating birds adapt to changing seasons

Birds that fly long distances across continents in spring are more flexible in adapting their migrations to a changing climate than they’ve been given credit for, according to new research.

The study, published in the journal Proceedings of the National Academy of Sciences, suggests the birds’ rapid population declines are more likely a result of human land use and habitat destruction.

When spring arrives, flowers bud, insects come to life, animals leave hibernation and birds follow rich new bounties so they can feed and mate.

This complex mosaic of interrelated events, or spring phenology, is being disrupted by climate change. But there are inexplicable differences in the timing of life cycle patterns within and between species, including bird migration.

Populations that travel long distances are waning much more quickly than those that stay home or migrate short distances – an alarming phenomenon that has been popularly attributed to climate change.

But how and why is unclear, write Birgen Haest, from the Institute of Avian Research in Germany, and co-authors, and this has been difficult to assess because of uncertainties about their movements between stops.

To shed light on the matter, the team turned to six species of intrepid trans-Saharan migrators: the European pied flycatcher (Ficedula hypoleuca), common redstart (Phoenicurus phoenicurus), willow warbler (Phylloscopus trochilus), common whitethroat (Sylvia communis), garden warbler (S. borin) and spotted flycatcher (Muscicapa striata).

They investigated the impact of weather variables on the birds’ spring migration patterns, which pass the German island of Helgoland, between 1960 and 2014.

The search covered an expanse from northern Scandinavia to Cameroon, and Iceland and the Canary Islands to Poland, Greece, Libya and Chad.

Results showed that, as for short-distance migrants, weather conditions at wintering grounds and spring stopovers accounted for around 80% of variations in long-distance migration patterns.

Intriguingly, more favourable wind patterns helped them arrive at their spring hangouts earlier, which drove advanced migration more than rising temperatures over the 55 years.

The scientists say their findings suggest discrepancies between variables used until now “has led to a consistent underestimation of the flexibility of long-distance migrant birds in spring migration onset from the wintering areas”, leading to “false assumptions”.

It has important implications for future evaluation of climatic impacts on bird survival, they conclude.

“A better understanding of climate change influences on the timing of biological phenomena is vital to understanding and ultimately battling the consequences of climate change on population demographics.”