(CNN)Nightingales may be less likely to survive their annual migration because climate change is causing the songbirds to evolve shorter wings, new research has found.
Scientists discovered that over the past two decades, the wingspan of nightingales from central Spain has decreased.
They highlighted natural selection caused by rising average temperatures in the region as the likely cause of the trend.
Nightingales flock to sub-Saharan Africa every year, but the researchers from the Complutense University of Madrid warned that the birds find it harder to return if their wingspans are stunted. Their study was published Wednesday in the journal The Auk: Ornithological Advances.
"There is much evidence that climate change is having an effect on migratory birds, changing their arrival and laying dates and their physical features over the last few decades," lead author Carolina Remacha said in a statement.
"If we are to fully understand how bird populations adapt to new environments in order to help them tackle the challenges of a rapidly changing world, it is important to call attention to the potential problems of maladaptive change," she added.
In Spain, the spring season has shifted later in the year and droughts over the summer have become longer and more intense, meaning nightingales have a shorter window in which they can raise their young, the team said.
That timetable has led to the more successful birds having smaller clutches (or groups of eggs), which affects wingspan and potentially other important survivalist features because of the unique way the songbirds' genes interact.
The "migratory gene package" theory dictates that a number of features which help nightingales survive their migration -- including wingspan, a high resting metabolic rate, shorter lifespans and larger clutches -- all interact with each other, so if one is negatively affected, all the other can be weakened too.
That means having fewer offspring due to a warming climate is likely also responsible for the birds having shorter wingspans, the researchers said.
The impact of climate change on numerous bird species has been well documented.
Research by the National Audubon Society last year found that two-thirds of North American bird species — 389 different species -- are at risk of extinction from climate change.
Another independent study said that said nearly 3 billion birds have disappeared from the United States and Canada in the past half a century.
And further research in 2019 stated that the sizes of birds in the US has changed over the past four decades, likely as a result of the changing climate -- although that study found that the birds' bodies were shrinking but their wingspans were getting wider.