Migratory birds including the willow warbler, the garden warbler and the nightingale may eventually stop flying south for the winter as they spend longer in their European breeding grounds.
Analysis of more than 50 years of bird records from the Gambia and Gibraltar has found that some migratory species that cross the Sahara are spending between 50 and 60 fewer days on average in Africa each winter.
The study, published in the journal Global Change Biology, examined changes in arrival and departure dates in the Gambia and Gibraltar alongside changes in climate and vegetation.
While it was previously thought that birds timed their seasonal migration based on daylight hours, the analysis suggests that birds are making more nuanced decisions based on available vegetation and climatic changes.
Records from 1964 to 2019 analysed by scientists at Durham University found that species were arriving at their winter destinations later in the autumn than in the past and also departing these locations earlier in the spring, reducing the amount of time spent in their winter homes.
Over a 27-year period, migratory birds including reed warblers, northern wheatears and common whitethroats were found to increase their time in Europe by 16 days on average.
Lead author Kieran Lawrence at Durham said: “If the trends we have seen in this study continue, we may see that, in time, some birds will spend no time at all in sub-Saharan Africa, and instead spend the full year within Europe.”
Many of these small migratory birds are suffering significant declines in their British populations, with nightingales in danger of extinction and England’s breeding willow warblers down by 45% in the past 24 years. But populations of chiffchaff, a short-distance migrant that mostly overwinters in Europe or north Africa, have increased by 114% over the same period.
While a reduction in migration could help some species survive, Lawrence said there were wider potential implications in both Europe and Africa. “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,” he said.
“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.”
Global heating has already changed some patterns of short-distant migration to Britain, with many more blackcaps now spending winter in the country rather than moving to continental Europe. In Europe, the white stork has reduced its migration to Africa, with many birds wintering on the Iberian peninsula rather than moving farther south.
Co-author Clive Barlow, a bird expert from the Gambia, said: “It is very satisfying to see the constructive way the Gambian migrant bird records, collected by dedicated ornithologists over many decades, are now being used to highlight the changing migratory patterns of these species. Until the current research, no one had realised the extent to which migrant birds are spending less of the year in sub-Saharan Africa.”
