Migratory birds from South and Central America begin their annual trek northward to breed in the continental United States during the spring. However, the exact day on which they first appear in the spring varies from year to year. This fluctuation has been connected to large-scale climatic patterns that originate thousands of miles away, according to the findings of a research that was headed by NASA and published in the Bulletin of the American Meteorological Society (Bulletin of the American Meteorological Society).
Migratory birds contribute to the health of ecosystems by pollinating plants, controlling insect populations, and providing a food source for other forms of animals. The more land managers know about the migration patterns that these birds follow currently – as well as the migration patterns that are likely to develop in the future as a result of climate change – the better they will be able to direct their efforts to protect the birds and to restore and conserve their habitats. The results of this research put them one step closer to achieving that objective.
The researchers examined 23 years’ worth of data on bird migration that had been gathered by NOAA’s Next Generation Radar system, which is comprised of 143 radar stations spread across the continental United States. Their goal was to determine the degree of variation in the arrival times of the birds each spring. This is where they made their first finding, which was that the United States could be broken up into two separate zones, east and west, and that each of these regions had a unique pattern of variability in the arrival times of birds.
All locations to the east of 102 degrees west longitude are considered to be part of the east region. This is a line that, in the United States, cuts through North Dakota and continues on into Texas. The locations that are west of that line are considered to be part of the west region.
The monitoring of bird migration in the United States takes place within the framework of four “flyways,” also known as principal migratory routes; two of these flyways are located in the eastern United States, while the other two are located in the western United States. The current study investigates the varied impacts that act on either half of the nation and alter the timing of environmental signals, such as temperature and weather patterns, that urge birds to migrate along their flyway. These environmental cues include temperature and weather patterns.
According to Amin Dezfuli, a scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is also the lead author of the study, “Our approach doesn’t replace the ‘flyways,’ but rather introduces a different geographic framework that reflects the interannual variability of bird migration at the continental scale.” This statement was made by Dezfuli. “Using this approach, we are better able to comprehend how broad-scale climatic variations impact the migratory patterns and variability of birds,” the authors write.
The research group examined the data that was generated by meteorological and climatic models for each of these newly defined zones in order to determine what factors were responsible for the variable bird migration that occurred in each of them. The researchers discovered that the fluctuation in the western area was significantly connected to the regional air and sea surface temperature in the nearby (Pacific) Ocean. For example, in 2005 there were above-average temperatures in the area, which led to the birds coming sooner than they normally would have.
However, they discovered that the fluctuation in the eastern area was more closely connected to large-scale atmospheric disturbances known as Rossby waves. Rossby waves are created when the rotation of the Earth combines with the Earth’s topography. They contribute to the movement of warm air from the tropics toward the pole and cold air from the polar regions toward the lower latitudes. They move from east to west and may be thousands of kilometers long. They have an effect on the patterns of weather and climate.
“Using the climatic data, we were able to correlate the bird migratory patterns, particularly in the eastern portion of the United States, to Rossby waves,” said Dezfuli. “This was notably true in the eastern region of the United States.” “Rossby waves may be initiated hundreds of kilometres away in the tropical Pacific, and they can propagate all the way over to the United States, creating the climatic conditions we associate with these bird migratory patterns.”
Because Rossby waves can be as long horizontally as the country itself, a peak in the west can bring warm temperatures to that region, while a low-pressure trough in the east can bring cooler temperatures and storms to the eastern region at the same time. Both of these effects are caused by the fact that Rossby waves can be as long as the country itself. Because of this, eventually, bird migration is affected in both locations.
According to co-author and Colorado State University biologist Kyle Horton, “knowing the time of migration is crucial to our overall knowledge of migration systems.” “Knowing the timing of migration is fundamental to our overall understanding of migration systems.” “This work adds a new and crucial layer to this knowledge, emphasizing how intertwined migratory systems are with atmospheric circulation – both close by and far away.”
Dezfuli is now considering the ways in which these findings could be used in the foreseeable future.
“Now that we have established regionally specific associations between climate variability and bird migration patterns, we could next investigate the potential changes in migratory patterns under future climate scenarios,” said Dezfuli. “Now that we have established regional-specific associations between climate variability and bird migration patterns.”
When scientists and other stakeholders have more information about the consequences that climate change will have on bird migration, they will be better able to plan to safeguard these species and the ecosystems that they depend on.
