Billions of US birds are migrating sooner due to climate change, study shows 

Climate change is causing birds to migrate earlier in the spring to find food and reach breeding grounds before they are ‘crowded out’

  • US migratory birds are passing certain stops sooner in spring than 20 years ago
  • Dramatic shifts were found in places where temperatures are rising quickly
  • Changes brought on by climate change as birds reach breeding grounds sooner 
  • Study representing billions of birds found shifts were less apparent in autumn

Hundreds of species of birds are migrating earlier in the year than they did 20 years ago, according to a new study – and it’s all down to climate change.

US researchers used AI and big data to crunch 24 years of radar data on the night-time migratory behaviours of hundreds of bird species – representing billions of birds in total.

They found that birds that have synchronised their migration with the availability of food – which is influenced by climate change – now find their migratory clock out of kilter.  

Temperature and migration are so closely aligned that the greatest changes in migration timing occur in the regions of the US that are warming most rapidly.

The changes were more pronounced during the spring migration than in the autumn, as birds rush to reach breeding grounds and find mates before they are ‘crowded out’ by competitors. 

Researchers used a new big data tool developed to study nighttime migratory behaviours of hundreds of species representing billions of birds, including this Northern Waterthrush

‘In the spring, we see bursts of migrants, moving at a fairly rapid pace, ultimately to reach the breeding grounds,’ said lead author Dr Kyle Horton.


Migration is typically driven by the availability of resources such as food, mates, or the accessibility of nest sites.

Birds tend to migrate northward in the spring to take advantage of an abundance of food sources and nesting locations.

As winter approaches and the availability of insects and other food drops, the birds return south to tropical regions that have replenished in the meantime. 

‘However, during the fall, there’s not as much pressure to reach the wintering grounds, and migration tends to move at a slower, more punctuated pace.’

Access to food can impact when birds travel, including factors such as the timing of blooming vegetation and the emergence of insects.

Due to climate change, these factors may now be out of sync with the passage of migratory birds and even subtle shifts could have negative consequences for their health.

And the observed shifts don’t necessarily mean that migrants are keeping pace with climate change.

‘Bird migration evolved largely as a response to changing climate,’ said senior author Andrew Farnsworth of the Cornell Lab of Ornithology.

‘It’s a global phenomenon involving billions of birds annually. And it’s not a surprise that birds’ movements track changing climates.

‘But how assemblages of bird populations respond in an era of such rapid and extreme changes in climate has been a black box. Capturing scales and magnitudes of migration in space and time has been impossible until recently.’

Birds can travel thousands of miles to navigate to their nesting grounds

Birds can travel thousands of miles to navigate to their nesting grounds

The authors believe it’s one of the first studies to examine climate change impact on the timing of bird migration.

The team used a machine learning tool called ‘MistNet’, developed by Professor Dan Sheldon at the University of Massachusetts Amherst, which helps identify anomalies in images of birds.

While a person previously had to look at each radar image to determine whether it contained rain or birds, the system detects patterns in radar images and removes rain automatically.

Using cloud computing, the team crunched the numbers in about 48 hours

To process all the data without cloud computing would have taken more than a year of continuous computing.

‘To see changes in timing at continental scales is truly impressive, especially considering the diversity of behaviours and strategies used by the many species the radars capture,’ said lead researcher Kyle Horton at Colorado State University.

The average peak migration timing advanced in spring and autumn and these changes were generally more rapid at higher latitudes.

They made maps of where and when migration occurred over the past 24 years. By animating these, they discovered that the most intensive migratory areas were in a corridor near the Mississippi River. 

The team sampled 2,115 spring nights and 2,152 autumn nights with a total of more than 13 million radar scans from 1995 to 2018.

In the future, the team plan to expand their data analysis to include Alaska, where climate change is having more of serious impact that the lower 48 US states.

The study was published in Nature Climate Change.