Geography asks three questions:... migrate, that is!
According to the tracking site BirdCast, this past Tuesday evening saw record-breaking levels of bird migration across North America.
The map brings two spatial observations to mind. The first is the importance of the 100th meridian (100ºW longitude) -- a line corresponding roughly to the 20-inch isohyet and evident on a surprising variety of North American maps.
The second is the vivid reminder of the importance of the Rio Grande Valley to migratory birds. When we lived there from 1994 to 1997, we became aware that the greatest bird biodiversity in the country is observed in the handful of counties at the southmost tip of Texas. Several hundred species of birds (more than half of the U.S. total) have been observed in just two locations Aransas National Wildlife Refuge and Santa Ana National Wildlife Refuge.
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| This map is taken from my Texas County map page, in turn taken from my friend who created it for the regional Chamber of Commerce back in the day. |
The latter was much closer to our home in Pharr, and we enjoyed a rich diversity of migratory birds there -- a single square mile that was occasional host to about 400 species of birds. Both sites are important because of the overland portion of the flyways converging -- with many birds essentially funneled between the Rocky Mountains and high plains to the west and open water to the east. Birds following the eastermost flyways tend to do island-hopping as they skirt that side of the Gulf of Mexico.
I include a somewhat outdated map of the Lower Rio Grande Valley for several reasons, even though it does not show these refuges. Aransas NWR is a bit to the northeast -- just beyond the northern end of Padre Island, and Santa Ana is just to the south of Alamo (the town, not the San Antonio fort). What the map does show is that this is a largely urban corridor, with important highways and bridges in every direction -- a real challenge for preserving habitat, even for birds -- and even more importantly for large cats. Every acre of land matters, and I was involved with the Rio Grande Sierra Club in several efforts to preserve what remained. We were especially interested in maintaining corridors of connection between available patches of habitat -- this sometimes required rethinking the construction of bridges so that wildlife could transit under the roadway and along the floodplains.
It is also worth noting -- for those not familiar with Texas geography -- that the Rio Grande Valley is not a valley at all. Rather, it is the very large, very flat delta of the Rio Grande / Rio Bravo. The lower 100 miles or so of this 1,896-mile river flows through a very large triangle of very flat land.
Not Just Birds
The migration of birds made living in the Valley even more interesting than it otherwise was; I especially enjoyed certain evenings of my 108-mile commute to the town of Alice during seasons in which scissor-tailed flycatehers or red-tailed hawks would race my car in their hundreds.
This is also an important corridor for monarch butterflies and was the first point of entry for Africanized "killer" bees, which we did observe at Santa Ana NWR. I knew what they were, because I had been mildly swarmed by during my first visit to the Amazon. This is a sound one does not forget!
Finally, of course, migration across this border by humans is immensely important and is lately the subject of much misinformation, abuse, and misguided wall-building.
Lagniappe
I am reminded of what Nixon's (criminal) Attorney General John Mitchell had to say on the subject:
"The conservation movement is a breeding ground of communists and other subversives. We intend to clean them out, even if it means rounding up every bird watcher in the country."
We thought Nixon was the worst -- and at the time he was -- but even he ended up signing many landmark environmental laws, including the Endangered Species Act.
