Fall's Journey South
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Millions of Migratory Birds Move Through The Lower Rio Grande Valley/Santa Ana National Wildlife Refuge Complex, Alamo, Texas
November 10, 1997
"It's really awe-inspiring to walk the trails or sit beside the wetlands this
time of year as millions of songbirds migrate through the area," marvels Dave
Blankinship, biologist at Lower Rio Grande Valley/Santa Ana National Wildlife Refuge
Complex. "Thousands of hawks, shorebirds, and waterfowl are also descending
on the refuge and waves of them are still coming."
Over 410 species of birds--from hawks to hummingbirds, shorebirds to waterfowl, and many colorful songbirds such as warblers, tanagers, thrushes, flycatchers, vireos, and many others--either live year around, or migrate through, the Lower Rio Grande Valley/Santa Ana National Wildlife Refuge Complex. There are few places on the North American continent that see so many different species of birds. Why do you think such a large number of bird species come to this area?
Location, Location, Location
If you are thinking about location, location, location of the refuge, you are on
the right track. Similar to Cape May National Wildlife Refuge in New Jersey, and
Cape Charles in Virginia, the Lower Rio Grande Valley/Santa Ana National Wildlife
Refuge Complex is located at the bottom of the tip of a land-funnel in south Texas.
Locate the refuge on the map and you can see that birds from the eastern and mid-western
regions of the continent funnel into this area.
In fact, the Lower Rio Grande Valley/Santa Ana National Wildlife Refuge Complex is located at the convergence of two major flyways, the Mississippi and the Central flyways. The Atlantic, Mississippi, Central, and Pacific flyways are general routes which birds tend to migrate along. Because birds are funneling into the Lower Rio Grande Valley from both the Mississippi and the Central flyways, a great number of different species stop down at the refuge and surrounding areas. Ever since fall migration began in late August, birds have been drifting southward across the continent. They have been moving through the area since mid-September. Fall migration takes place at a more leisurely pace than spring migration when birds race to get to their breeding grounds.
Birds of the Neotropics
Many of birds that migrate through the Lower Rio Grande Valley are known as "Neotropical"
migratory birds, or birds which nest in the United States or Canada, and spend the
winter months in Mexico, Central or South America, or the Caribbean. 346 species
of birds in the Western Hemisphere are Neotropical migrants. A whopping 196 of these
stop down to rest and refuel at the Lower Rio Grande Valley/Santa Ana National Wildlife
Refuge Complex! Tens of thousands of bird watchers come to the refuge complex each
year to spot Neotropical songbirds, hawks, shorebirds, and waterfowl as well as the
resident birds.
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From the Lower Rio Grande Valley/Santa Ana National Wildlife Refuge Complex, the Neotropical migratory birds will move on to Mexico and points south. Depending on the weather in any given year, some species will migrate down the coast of the Gulf of Mexico while others will take off over the Gulf. Because the refuge complex is right on the Mexican border, it is a crossroads of migration and hundreds of thousands of birds continuously fly back and forth between the United States and Mexico. Are migratory birds the only Neotropical migrants? What about humans? Can you think of reasons why citizens of the United States and Canada go south to Mexico, Central and South America, and the Caribbean? Why do you think people of these regions come north to the United States and Canada?
Populations in Danger
Some biologists worry that populations of some Neotropical migratory birds are declining.
The Neotropical migratory songbirds seem to be at greater risk than resident songbirds.
Why do you think this is so?
Because Neotropical migratory songbirds travel over such long distances, they are vulnerable to loss of forest, grassland, wetland, and coastal habitats in their breeding grounds, wintering grounds, and a huge number of stop-over points along the way. When their breeding, and stop-over habitats are lost to development in the United States and Canada, or the tropical and semi-tropical forests are cut for agriculture and cattle ranching in their wintering grounds, populations of some Neotropical migratory songbird species have declined.
Biological Riches
The Lower Rio Grande Valley/Santa Ana National Wildlife Refuge Complex is located
in the river delta at the extreme southern end of the Lower Rio Grande Valley, which
stretches for approximately 800 miles from El Paso, Texas to the Gulf of Mexico.
The Rio Grande River (known as the Rio Bravo in Mexico) runs down the middle of the
Valley and forms the border between Mexico and the United States. It connects the
two countries and is a wellspring of life for people, animals, and plants of Mexico
and the United States. Four major climactic zones occur in the area and average rainfall
ranges from nine inches near El Paso, Texas to 26 inches near the Gulf of Mexico.
This makes for a great diversity habitats, providing many different types of homes
for the large number of bird and other wildlife species that live in the area.
Wildlife Corridors Provide a Land Bridge In recent years, portions of the Valley have experienced rapid population growth and expansion of agriculture and maquiladora industries (factories which are built in Mexico to take advantage of cheap labor but whose products are exported to U.S. markets), in part associated with passage of the North American Free Trade Agreement in 1994. Because the Valley is so important to migrating wildlife, biologists and other conservationists are developing a wildlife corridor called the "Lower Rio Grande Valley Wildlife Corridor." A wildlife corridor is a series of land areas linked together in a kind of habitat land-bridge for birds and other wildlife. The Lower Rio Grande Valley Wildlife Corridor is envisioned as a continuous ribbon of habitat stretching across four counties in south Texas.
Look at a map of your county. How many green spaces can you find? Where are they located? Are there ways that any of these could be linked together by protecting areas that lie between them. How could an "Unpave the Way for Wildlife" project at your school help provide a series of stepping stones or contribute to development of a wildlife corridor in your area?
The Next Journey South Update Will be Posted November 17, 1997.
- How You Can Help Track Fall's Journey South
- How You Can Help Track Spring's Journey North
