By all accounts, the ranchera duo Las Jilguerillas are among Mexico's greatest and most enduring musical treasures. Sisters Imelda and Amparo Higuera, who hail from Michoacan, began singing together as children and were discovered by another famous Mexican duo, Dueto America, comprising Carolina and David Gonzalez. In fact, Las Jilguerillas are considered their successors. For more than 40 years, their music has adhered to strictly rural styles, primarily ranchera, but also banda, son, and corridos, always in rural style. Imelda has been the lead voice accompanied in harmony a...