More frequently heard than seen, the Mexican Whip-poor-will is an elusive and poorly known nightjar that occupies humid to semiarid 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.