Study Finds Bird Migration Timing Skewed by Climate Change

Weather Radar Detects Change on a Continental Scale

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The timing of spring bird migration across North America is shifting as a result of climate change according to a new study in Nature Climate Change.

The study is a collective effort by scientists at Colorado State University, the Cornell Lab of Ornithology, and the University of Massachusetts, and is one of the first to examine the subject at a continental scale.

Using 24 years of weather radar data, findings indicate spring migrants are likely to pass certain stops earlier now than they would have 20 years ago.

Dickcissel_Kyle_Horton_web
Dickcissels migrate to their breeding range rather late, with the first arriving only in May, and most birds only arriving in early June. Photo credit: Kyle Horton

Migration Timing

Temperature and migration timing is closely aligned.

Scientists say the most significant changes in migration timing occurring in regions warming most rapidly.

During the fall, shifts in migration timing are less apparent.

“To see changes in timing at continental scales is truly impressive,” says Kyle Horton, an assistant professor at Colorado State University.

“Especially considering the diversity of behaviors and strategies used by the hundreds of species the radars capture.”

Horton says the timing shift doesn’t necessarily mean that the birds are keeping pace with climate change.

And there’s concern about a mismatch between when birds arrive and when the blooming plants and insects they need for food are at their peak.

Peak abundance for seeds, fruits, and insects is known to be occurring earlier than it used to (green line). The question posed by this animation is whether or not birds can shift their migration timing enough to stay in sync with peak food availability. Animation by Kyle Horton.
Peak abundance for seeds, fruits, and insects is known to be occurring earlier than it used to (green line). The question posed by this animation is whether or not birds can shift their migration timing enough to stay in sync with peak food availability. Animation by Kyle Horton.

Bird Migration Tracks Changing Climate

Andrew Farnsworth, a researcher at the Cornell Lab of Ornithology, says the team’s research answers some key questions.

“Bird migration evolved largely as a response to the changing climate,” he says.

Farnsworth says migration is a global phenomenon involving billions of birds annually.

And it’s not a surprise that bird movements track changing climates.

Long-billed_Curlew_Nick-Saunders_web
The Long-Billed Curlew is a short-distance migrant and one of the earliest breeding shorebirds, returning from wintering grounds from California to Mexico in mid-March. Photo credit: Nick Saunders

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He says how bird populations respond in an era of such rapid, and extreme changes in climate have been a black box.

Capturing scales and magnitudes of migration change over time has been impossible until recently.

The study authors find the lack of change in fall migration patterns surprising.

But say migration also tends to be a “little bit messier” during those months when there’s not the same pressure to reach wintering grounds, and migration tends to move at a slower pace.

The researchers plan to expand their data analysis to include Alaska, where climate change is occurring faster and having more serious impacts than in the lower 48 states.

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