Most of the U.S. migratory species stay or pass through Mexico at some point in their lives.
For example, the Grey whale feeds during summer months near Alaska and reproduces during winter months in the Baja Peninsula in Mexico. If it was only protected while in US waters this species would have disappeared long ago. But this species is protected by the International Whaling Commission moratorium on whaling, by CITES through its Appendix I list that prohibits international trade and by Mexican environmental laws.
Of the nearly 800 species of birds known to occur in the US, around 500 are migratory, most of which migrate to the Caribbean and Latin America. Of these, 225 species migrate in Mexico with 75 of them wintering no farther south. Many of these birds are classified as threatened or endangered and face numerous threats while migrating. Defenders International team makes sure that protections remain in place for birds as well as sea turtles, sharks and many other migratory species by working with lawmakers, environmental leaders and fishery authorities in Mexico.