I gather from the rangers that getting a job at this particular refuge is welcome, providing you are interested in any kind of biology and don't mind frequent visits from the Border Patrol. The major city in the lower Rio Grande valley is Matamoros, Tamaulipas, which continues on the U.S. side of the river as Brownsville. The two National Wildlife Refuges that I visited are marked on the map in letters befitting their interest, at least in comparison to the cities around. Underlying map copyright 1999 Microsoft Corporation. The refuge landscape consists mostly of something called thorn woodland, interrupted by meadows and oxbow lakes.
Most trees are mesquite, with some oaks, willows, and a few gymnosperms.
Evidently, the lower Rio Grande Valley once all looked like this, but now most everything outside the refuge is either a farm or paved. Prickly pears Opuntia spp. That's the Rio Grande, with Texas plants on this side and remarkably similar Tamaulipas plants on the other. The water moves quickly and is green. I had no fish or frogs to offer the night-heron, so it was less impressed on meeting me than I was on meeting it.