Mating Cuban crocodiles and American crocodiles are creating hybrid offspring that threaten the survival of the Cuban species, which has dwindled to about 4,000 wild animals in two isolated Cuban swamps. The ten-foot-long (three-meter-long) reptile is listed as critically endangered by the International Union for Conservation of Nature (IUCN).

"That means any loss of animals—be it loss in fact or loss through hybridization—is a grave concern," said John G. Robinson, executive vice president for conservation and science at the Wildlife Conservation Society.

American crocodiles, which are found throughout the Caribbean, are not considered threatened by IUCN. The animals have increasingly moved into the Cuban crocodile's remaining freshwater habitat as it becomes more brackish—or salty—due to agricultural activities, said Robinson, who was