Yellow Warbler

Yellow boat taken out of Puerto Rico’s Cabo Rojo. This migratory bird breeds in North America and winters in Central / South America and the Caribbean. Image by Luis O. Nieves

Four hundred million birds are expected to be on flight tonight across the United States. That’s right: 400 million!

The annual migrations of birds represent some of the most spectacular animal movements on our planet, with an enormous number of individuals hundreds, thousands, and tens of thousands of miles each year. There are billions of birds migrating annually between the temperate or non-Arctic latitudinal breeding sites of North America and the neotropical winter lands of the Caribbean, South, and Central America. This Nearctic-Neotropic system, as it is known, evolved over the last 65 million years as the climate of North America changed, at a time when the belt of the entire continent, consisting of relatively mild and humid conditions, was separated by a patch of tundra, forest. pastures, and deserts with extreme temperature and precipitation regimes. Birds began to migrate in search of milder climates, seeking better resource availability and less competition or prey.

Bird habitats, migratory corridors, and resting and refueling stops can affect the weather. Although migratory birds have an impressive set of weather-sensing skills — including changes in wind, visibility, and air humidity, and barometric pressure assessments — they may not always be able to avoid bad, harsh weather, especially when traveling on water.

migratory routes of birds and traces of hurricanes
A map of the typical routes of tropical Atlantic hurricanes (red, from the National Hurricane Center), superimposed on broadly defined migration routes. Birds can encounter storms along the Atlantic (green), Central (orange) and Pacific (blue) migration routes of the Americas.

The Gulf of Mexico is one of the most populous migratory corridors for birds in the Western Hemisphere. More than half of the North American species that spend the winter in the tropics have to negotiate in the Gulf of Mexico by flying twice a year or so. Analysis of weather radar images has revealed that approximately 4 billion migratory birds pass through it every year. Of all the bird biomass migrated to the Neotropics in the fall, approximately 76% returned to net loss due to mortality during the spring, migration period, and winter.

It has been known that hurricanes move or kill birds, as a result is often called a “disaster” by a bird. The most common routes of Atlantic hurricanes traverse all or some of the non-Arctic-Neotropical migratory birds. In the 2020 book Furious Sky: Five Hundred Years of History of American Hurricanes, Eric Jay Dolin reports on the history of birds displaced by hurricanes.

Southern Cuba in October 1780, by the British Royal Army HMS Phoenix After Jamaica equalized, he was faced with a rapidly closing storm. First Lieutenant Benjamin Archer said the birds “came out of the sky and plunged back, many of them unconscious.” He also hit Long Island and New England in the Great Gale in September 1815, as lexicographer Noah Webster noted how the Massachusetts sea escape was carried inland along with seagulls, “some of which exploded as far as Worcester, about 45 miles from the ocean.” Hurricane Wilma 2005, thousands of chimneys they died or moved thousands of miles, which was marked by a marked decline in the breeding population.

Radar and ground observations showed that in 2011 Hurricane Irene sent tropical birds north to New York. Now, the rapidly changing climate is overloading this important threat of migratory birds: those with high and extreme intensities of tropical storms and globally classified as cyclones in categories 3, 4 and 5 are on an upward trend.

Fisherman Martin
Every year, Belted Kingfishers migrate in the fall from Canada to Puerto Rico while traveling to Mexico and Central America. Image by Luis O. Nieves

It is particularly important to know that near-Arctic-Neotropical migratory birds are currently killing or displacing hurricanes in the Atlantic Basin. Last week, federal wildlife officials counted 23 species as extinct, including 11 birds, including the well-known ivory woodpecker. North America’s avifauna has shrunk by almost 30% in the last half century – a huge loss of nearly 3 billion birds. The small increase in winter bird deaths from the United States to the south can also lead to significant population declines.

Few studies have shown that tropical cyclones in the Atlantic can harm populations of some migratory bird species, but the impact of tropical cyclone activity on changes in regions or large-scale migratory intensity has not been measured so far. Earlier this year, I learned from the tips and recommendations from tutors Andrew Farnsworth and Benjamin Van Doren at the Cornell Lab of Ornithology, and through Phil Klotzbach, at Colorado State University’s Tropical Meteorology Project, I looked at the impact of tropical cyclone activity on the Neartic. -Neotropic migratory birds in Johns Hopkins University thesis.

seen from above from the eye of the hurricane
Hurricane Irma, the strongest storm ever recorded in the Atlantic Ocean, is heading for the eastern Caribbean in this September 5, 2017 satellite photo. Image from the public domain by NOAA.

The inverse relationship between the number of migratory birds in or near the Gulf of Mexico in the spring and the frequency and intensity of active summers in late summer and autumn suggested a correlation between direct storm mortality and the number of birds. In other words, stronger and more frequent hurricanes are expected to result in more dead birds during migration in the gulf. It makes intuitive sense, but my researchers and I wanted to prove it in the world of science. Our research has applied emerging techniques to processing weather radar signals to compare the number of migratory birds in the autumn with those returning in the spring, examining common migratory corridors in parts of the Gulf of Mexico and the Atlantic coast of the United States since 1995.

The results of my research, which have not yet been reviewed, have shown that very active hurricane seasons are associated with a reduction in the number of neotropic migrants returning next spring. When Atlantic hurricane seasons were very active (i.e. more than 90% of typical hurricane seasons), the number of birds passing over and near the Gulf of Mexico the following spring was about 20% lower than when migrations continued. storm seasons with very little storm activity (in other words, hurricane season activity was weaker than 90% during hurricane season).

Although this finding may suggest that the storm could have directly affected birds or damaged flights, additional research on storms created in the Atlantic subregions confused this premise. The activity of tropical cyclones measured in the open North Atlantic Ocean increased with declining migratory transit, with a weak relationship between storm activity in the Gulf of Mexico and birds migrating across the Gulf, although home. in many important migratory corridors of birds. The same thing happened after watching the migrations of birds across the Gulf of Mexico after the Caribbean storms – little effect was seen. Thus, a direct, simple, individual, and direct causal relationship between storms, mortality, and fluctuations in observed passages occurs. Instead, a combination of factors is likely to cause bird losses, although only one of them has a direct impact on the storm, although this is not entirely clear from the results obtained so far.

Thermal imaging cameras are sometimes used to capture infrared images of birds flying at night.

What is likely to happen here is what researchers refer to as “teleconnection,” which is a causal link between short-term climate patterns in one place and meteorological or environmental conditions that occur far away in other places later. A well-understood example is the teleconnection between El Niños, which is thousands of miles across the North Atlantic Ocean, or La Niñas in the eastern Pacific Ocean.

These short-term climate changes also affect wintering places and wind migrations of neotropical birds; environmental conditions, in turn, may affect the physical condition or survival of migratory birds. Although the decline in Atlantic tropical storm activity in El Niño during the year may be met by a storm of weather in the fall, birds can move to drier places in winter when El Niño occurs. In other words, the short-term climate variability patterns that drive seasonal activity in Atlantic hurricanes also affect winter lands (plus winds along migratory routes), which can damage the overall status or survival of migrants.

Because birds can be affected by one or more of these teleconnection factors (such as drought, wind, and storms), it is difficult to measure the relative impact of each meteorological model on migratory birds — much less the combined net effect when many of them occur simultaneously. Some are for supporters and others for birds. The full spectrum of variables against migratory neotropical birds has not yet been elucidated. Other teleconnections that could affect bird migration could also be played, such as the North Atlantic oscillation.

Despite the underlying mechanisms, the first step is to find that the number of Neotropical migratory birds that return across the Gulf of Mexico in the spring and near the Gulf of Mexico in the spring and fall hurts the number of Neotropical migratory birds. further research. The methods used in my research can be easily replicated, which means that by 2025 it will be possible to have statistically robust data that can capture 30 years of Doppler radar information to make it meaningful for future scientists. So that opens the door for other scientists to do that research.

prediction of bird migration
Using the latest weather monitoring radar, the number of birds in a single night in the autumn migration can predict the number of birds, similar to weather forecasts. Image by BirdCast

Beyond the problems caused by human footprints, birds face increasing challenges as a result of changes in human climate. In the case of long-distance neotropical migratory birds based on greater survival, any increase in mortality may have important long-term implications for populations. Research on the links between weather, climate, and birds can be ongoing to understand bird behavior and the mechanics of ecosystems. conservation strategies would be improved to establish or reverse current downward trends in bird populations.

Rachel Carson once said “[T]here is a beauty as symbolic as it is symbolic of bird migration … something that is constantly healed in the repeated refrains of nature. ”Stronger hurricanes caused by changing climates and other man-made hazards will silence the chorus of this great wonder of the natural world.