In the United States,
a not-so-silent spring marks the arrival of several billion
birds migrating northward from Central and South America.
But curiously enough, the exact
timing of this journey varies each year.
So why is that?
The key to this mystery may not lie in looking at the traditional flyways,
but instead in radar, climate models, and a little bit of math.
At the Global Modeling and Assimilation Office,
we routinely produce a comprehensive
climate data set by combining observations and models,
and these are freely available to the public.
This data can be used to explain the characteristics
of ecosystems, like bird migration patterns.
In fact, by using a network of 143
NOAA radar stations across the continental United States,
the team analyzed 23 years of data to see if they could group stations
that had similar year-to-year variability in migration observations.
And this is different from the concept of flyways.
This is specifically looking at which radar stations across the United States,
in what regions have a similar
variability in bird migration timing.
What they found is that the U.S.
can be divided into two regions - east and west, each with its own
specific pattern of variability of migratory bird arrival times.
So now that we have divided the continental United States
into two regions, we can look at each region specifically
and understand the climatic drivers of this region.
The team found that the behavior of Rossby Waves,
huge waves of high-latitude westerly winds, was a major influence
for bird migrations in the East. As Rossby Waves
are triggered, particularly those in the tropical Pacific,
they influence climate patterns and bring warm temperatures to the eastern
United States, which in turn correlates with earlier arrivals of migratory birds
in that region.
Cold temperatures have the opposite effect.
Variations in the West, however, seem to be linked to more regional
climate conditions, such as sea surface temperatures of adjacent waters.
In this study, we tried to highlight the fact that we can use our data
for applications that would bridge climate science with other disciplines.
The team hopes that future research will build upon this study
to help us better understand how changes in the climate impacts specific
migratory bird species.