River Road Alterna Overview
|FM 170 is easily one of the
most scenic roads in the United States with outstanding
views into Northern Chihuahua, Mexico. A pilgrimage to
this area generally turns into an awakening for alterna enthusiasts
and serves to tie together the alterna experience in a way that can
never happen perusing snakes in deli cups at reptile
expositions. Simply put, for many, the place gets into
the blood like a fever that never quite goes away. Along
this long stretch of highway are several well know
collecting spots but alterna
can appear at just about anywhere along its length if
there is adequate roadside habitat. At Vivid Reptiles we
have narrowed our focus over the years to animals
originating from the "Big Hill" area - an impressive
desert mountain located about 12 miles west of the town
of Lajitas. Because of the scarcity of accessible
collecting spots, the sampling of alterna from all
River Road collecting spots is heavily biased and
undoubtedly many "surprises" lurk in the more
inaccessible areas to the north of the River Road.
To those unfamiliar with the species, alterna from the River Road can appear so radically different from the eastern types that they can be forgiven for making the assumption that they are not one and the same species. Indeed, regarding both pattern and color morphology - quite literally, anything goes. The clean, neatly laid out patterns of the eastern morphs can be rare here and although you can find light blair's phase animals here they are more often than not the exception. In River Road captive collections, blair's phase animals are not well represented because of collector bias rather than such animals being rarities. The River Road animals feature several, readily identifiable pattern types and the locality appears to be the geographic loci for the more flamboyant patterns involving speckling, multi-alternates, pin-banding and so forth. It is with much angst and frustration that we look south across the Rio Grande from the Big Hill and wonder what alterna variations lurk in the vast, unsampled desert expanses of Northern Mexico. Indeed, the true geographic origins for the aforementioned pattern types may well lie to the south of the Rio Grande.
Identifying River Road alterna by pattern/color is somewhat easier than identifying alterna from localities that lie to the immediate east and north. That said, exceptions do occur with enough regularity to keep one cautious. River Road signature features are readily identifiable in these proximal alterna localities and it would appear that the historic direction of gene flow has been from the River Road area outward to Black Gap to the east, the Christmas and Davis Mountains to the north and ultimately to the Guadalupe and Heuco Mountains to the northwest. Most of this gene flow likely occurred during the Pleistocene when migration barriers were much less reduced or altogether absent. One is left to ponder why so much variation and plasticity evolved in this species. Whatever the evolutionary forces were/are driving the evolution of this reptile, we have been presented with a treasure chest bursting with ophidian wonders. This is surely one of the most beautiful and varied colubrids on the planet.
For a compilation of significant features of River Road alterna please use the following button: