The increase in agricultural development in Sinaloa and Sonora in recent decades has caused important changes in habitats where the primary vegetation was originally lowland forest. The hydro-agricultural infrastructure, such as wells, dikes, and drains has supported the emergence of new niches that bird species are taking advantage of in both states. Despite numerous studies by ornithologists, the Mexican Duck (Anas diazi) has not been recorded on the Sonoran or Sinaloan coast. The species is listed under NOM-Ecol-059-2001 as threatened with extinction. Because the species has never officially been registered on the coast of these states, it is not considered of hunting interest under NOM-059. According to hunters and hunting clubs, however, approximately 300 or more individuals are hunted in the region every season. This project will (1) determine the distribution and abundance of the Mexican Duck in Sinaloa and Sonora during the breeding season; (2) document the different breeding habitats of the Mexican Duck in Sonora and Sinaloa: (3) determine the reproductive chronology and characterize the breeding habitat of the Mexican Duck in a site to be determined (Bahía de Santa María, Angostura Sinaloa, in Ejido Bachobobampo, Ahome Sinaloa or in Ejido La Trinidad, Guasave, Sinaloa); (4) begin a marking program for the Mexican Duck (both ducklings and breeding adults); and (5) determine if there are plumage differences between Mexican Duck populations in northwest Mexico and the rest of the country.