population. And as visitors to Laguna Atascosa know, 

 southern Texas has become a place to watch aplo- 

 mados in action. 



In the 1970s and 1980s, people had come to think 

 that regions farther west, such as the desert grass- 

 lands of Texas, New Mexico, and Arizona, were de- 

 void of nesting aplomados. But rare sightings of lone 

 falcons suggested the possibility of a population in 

 nearby Mexico. One of us (Montoya) became so cu- 

 rious that, in 1992, he and two other biologists — 

 Robert Tafanelli, then at New Mexico State Uni- 

 versity in Las Cruces, and Manuel Bujanda, now at 

 the University of Chihuahua, Mexico — began ex- 

 ploring the back roads of the Mexican state of Chi- 

 huahua. One day, as they were traveling through an 

 immense grassland with a scattering of tall yuccas, 

 they happened upon a pair of aplomados perched on 

 adjoining fence posts, preening nonchalantly in the 

 sunshine. During the next few years, Montoya, 

 Tafanelli, and Bujunda discovered nearly forty pairs 

 scattered among the cattle ranches of the region. 



Why did aplomados persist in Chihuahua, when 

 they had vanished from the U.S., only a few hun- 

 dred miles away? The answer has largely to do with 

 the history of ranching. In the U.S., by the 1870s, 

 the railroad had connected the grasslands of south- 

 ern New Mexico with the markets of the East, al- 

 tering the economics of cattle production. A sea of 

 fertile grasses, once largely inaccessible to livestock, 

 was opened up as trains carried equipment for 

 drilling wells and building windmills, earthen dams, 

 and watering tanks. The supply of grassland seemed 



limitless, and entrepreneurs showed little interest in 

 long-term sustainability. But the cattle caused mas- 

 sive erosion. Woody plants such as creosote bush and 

 mesquite moved in, smothering the open grasslands. 



Desert savannas in Mexico were affected far less 

 extensively than their counterparts in the U.S., in part 

 because the development of man-made water sources 

 for livestock in Mexico was so long delayed. Groups 

 of hostile Apaches on the Mexican side of the bor- 

 der in the late 1800s also made remote ranching risky 

 and unprofitable. The Mexican Revolution of 1910 

 further retarded the development of the region. 



The persistence of suitable habitat for nesting 

 aplomados in Chihuahua also owes much to 

 the long-established ranching families who man- 

 aged their lands with care through long cycles of 

 wetness and drought. Enrique Baeza, the owner of 

 a 100,000-acre ranch called the Tinaja Verde, in 

 eastern Chihuahua, belongs to such a family, and he 

 knows the aplomado well. To him, nesting aplo- 

 mados show how well he is caring for his ranch: 



My dad wanted to pass this ranch on to his kids, and that's 

 what I want to do for mine. The advice Dad gave me was 

 to graze as if [drought conditions] next year will be worse 

 than this one. That's what we do. We graze year round, 

 but we graze lightly — it's a tradition with us. Aplomados 

 are a thermometer for what we're doing. 



The thirteen pairs of aplomados nesting at Tinaja 

 Verde are indeed good indicators of the health of 

 the grasslands. They occupy a key node in a food 

 web that includes grasses, seeds, insects, and small 



