Many migrating birds are spending more time in their European summer breeding grounds, leading experts to consider whether long-distance migrations could become a thing of the past.
Researchers from Durham University’s Department of Biosciences led the study, which analysed over 50 years’ worth of bird-sighting data from The Gambia and Gibraltar.
The study, published in Global Change Biology, found that some species of trans-Saharan migratory birds, including nightingales and willow warblers, are spending over 60 days fewer in their winter non-breeding grounds compared to previous years. This suggests that birds are able to survive for longer in Europe than ever before.
Roughly half of the world’s species of birds are known to migrate annually between their summer breeding grounds and their warmer winter habitats. The availability of food is thought to be the biggest driver for migration, with other factors including escaping inclement weather.
Martin Wikelski, director of the Max Planck Institute for Ornithology, has said that “because migration is such an integral part of the avian lifestyle, it was likely almost as prevalent thousands of years ago as it is today”. These comments make the new findings even starker, highlighting that climate change is disrupting centuries worth of established behaviours.
Changes in environmental conditions, such as the length of days, air temperature, and weather conditions, may trigger migrations by stimulating hormones in birds. The study found that compared to 1964, birds are spending on average 63 days less in their winter habitats each year.
Such a significant reduction in time spent in Africa could be aided by the more temperate winters Europe has been having recently. The winter before last was the hottest on record for Europe, with temperatures 3.4°C above the winter average from 1981-2010.
Extended periods spent in Europe will only benefit birds if plant and insect populations mirror the trend, however, leaf bud-bursts and insect emergences are also reported to be happening earlier than in previous years.
The researchers related the observed changes to changes in the climate and vegetation in the two locations. Lead author Kieran Lawrence, a PhD student at Durham University, said “in Europe, the longer presence of traditionally migratory birds could lead to increased competition for autumn/winter food and resources for resident bird species that do not migrate”.
“Meanwhile, in the traditional migration destinations of sub-Saharan Africa, a reduction in the time migratory birds spend there could have implications for ecosystem services such as insect consumption, seed dispersal and pollination.”
The research team predicts that migrating patterns will change further in the future. Durham University’s Professor Stephen Willis, the project lead, added that they are developing a new model “to simulate these complex migrations, and which we can then apply to future scenarios to understand how the patterns we have identified in trans-Saharan birds over recent decades may continue or change.”
Image: Stephen Willis