Spring Bird Migration Happening Earlier for Some Birds

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With changes in temperature due to climate change, researchers looking at  24 years of radar data from the National Oceanic and Atmospheric Administration (NOAA) have found that migrating birds were more likely to arrive at certain stops earlier than they would have twenty years ago.  The research looked at the nocturnal migration patterns for hundreds of bird species.  By looking at the migratory patterns of billions of birds, researchers were able to study changes in spring migration at the continental scale.

Bird migration evolved in response to changes in temperature and precipitation as birds move through the spring season to regions that are more suitable for breeding.  As climate change influences regional warming, researchers have found that birds are responding by altering the timing of their migration.  Not surprisingly, researchers have found that areas, such as the high latitudes that are experiencing the most rapid warming, are also experiencing the greatest shifts in migration timing. Senior author Andrew Farnsworth of the Cornell Lab of Ornithology explained that this groundbreaking research is the first to look at climate-change driven migration at the continental scale. “Bird migration evolved largely as a response to changing climate. 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.”


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Fall migration did not show the same significant shift in migratory timing.  Lead researcher Kyle Horton at Colorado State University (CSU) explains one reasoning for this, “In the spring, we see bursts of migrants, moving at a fairly rapid pace, ultimately to reach the breeding grounds. 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.”

An analysis of 24 years of radar data shows a shift to earlier spring migrations, particularly for birds at higher latitudes where regions are warming more quickly. Figure: Horton et al., 2020.
An analysis of 24 years of radar data shows a shift to earlier spring migrations (a, b), particularly for birds at higher latitudes where regions are warming more quickly. Fall migration did not show the same significant shift in timing (c, d) Figure: Horton et al., 2020.

To analyze the massive amounts of radar data to differentiate between rain and bird migrations, an artificial intelligence (AI) system called ‘MistNet’ was developed to analyze 24 years of remotely sensed data.  Using a convoluted neural network trained on radar imagery, MistNet was able to identify 95.9% of all biomass on radar images with a false discovery rate of 1.3%.  The developed of this made analyzing the massive amount of data produced by US WSR‐88D, a networks of weather radars for the continental United States, possible.

The study

Horton, K. G., La Sorte, F. A., Sheldon, D., Lin, T. Y., Winner, K., Bernstein, G., … & Farnsworth, A. (2019). Phenology of nocturnal avian migration has shifted at the continental scale. Nature Climate Change, 1-6. doi:10.1038/s41558-019-0648-9

Birds’ Seasonal Migrations Shift Earlier as Climate Changes, New Research Shows.  University of Massachusetts Amherst.  December 16, 2019.

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