More frequently heard than seen, the Mexican Whip-poor-will is an elusive and poorly known nightjar that occupies humid to semi-arid forest from the southwestern United States south to Honduras. Until recently, this species was treated as conspecific with the Eastern Whip-poor-will (A. vociferus) (Chesser et al. 2010), despite long-known differences in voice and, to a lesser extent, morphology. The northern subspecies (A. a. arizonae), is migratory and withdraws from breeding areas in the southwestern U.S. and northern Mexico; the four other subspecies in Mexico and Central America are thought to be resident, although altitudinal migration may occur (Howell and Webb 1995).
The Mexican Whip-poor-will is nearly identical in appearance to the Eastern Whip-poor-will, although the two species probably overlap only during the overwintering period, in eastern Mexico and Central America. Male Mexican Whip-poor-wills have less white in the outer 3 rectrices and differ in their call, a rolling, trilled “g-prrip prrEE” that is lower-pitched, rougher and with a different rhythm than the loud, clear whistled "WHIP puwiw WEEW" or "Whip poor Will" of the Eastern Whip-poor-will (Sibley 2014).
Like many nightjars, Mexican Whip-poor-wills forage most actively at dawn and dusk. A ground-nesting species, it lays its eggs directly on leaf litter of the forest floor. However, the biology of the Mexican Whip-poor-will is essentially unstudied, largely due to its nocturnal activity and cryptic behavior—indeed, it it among the least-studied breeding species in North America. Their populations in the southwestern United States have been estimated to number 35,000 (Rosenberg et al. 2016); populations in Mexico and Central America are certainly much larger, but data are lacking. Studies on population demographics and the conservation status of this species are much needed.