Imperator subspecies of Boa constrictor are native all over the mainland in Mexico. However, the had not been known to occur in Cozumel Island along the southeast coast until the 1980ies.
Cozumel Island can be found 18 km east from shores of Yucatan peninsula. It features an area of 650 km², its population is 71.000.
Several mammal, bird and reptiles species are native there, but only few of them are predators. Although Boa constrictors are well-known to occur in the Mexican mainland, they had not been native to Cozumel until the 1980ies.
Their true origin had also been a mystery for a long time. Some sources claimed that those boas had reached to island from the mainland by using tree trunks. Considering the 18 km distance between Cozumel and the mainland it is unlikely that boas from mainland got the the island, even if they are very good swimmers.
According to another theory- which seems to be more likely now -, boas were brought to the island as decoration for filming a movie in 1971. After filming "El jardín de tía Isabel" had been finished, those boas were released.
Anyhow, boas adapted to their new enviroment very well, unfortunately for native rodents and birds. Boas pullulated in a short period of time by lacking their natural predator and competitor species. By the 1980ies they became so common, that several native bird species (Toxostoma guttatum) and rodent species (Reithrodontomys spectabilis, Oryzomys couesi cozumelae, Peromyscus leucopus cozumelae) become endangered due to boas invasive presence. Although, the true origin of Cozumel boas is not known, their ancetors were certainly from Quitana Roo state which is the closest state to Cozumel Island. As such, they represent the same morphological features like boas known as "Cancun boas" in captive collections that originaly came from Quintana Roo, as well.
In the nearest past, some TV channels and few biologist discussed this topic, but no solution have been made for that problem. Maybe this could a rare occasion when animal trade could help to remove invasive Boa constrictors from Cozumel. On the other hand, it is highly unlikely that boas could be totally eradicated from this island.
Christopher Lever: Naturalized reptiles and amphibians of the world
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