Rare avian species are being decimated by voracious rodents in the pristine Costa Rica island that inspired Jurassic Park. According to a recent news report filed by science journalist Michelle Soto of national newspaper La Nacion, four bird species in Isla del Coco (Cocos Island) are easy prey for rats that arrived on pirate ships nearly 500 years ago.

Ms. Soto’s report is based on a study conducted by biologist Nacy Orias of the University of Costa Rica, whose research revealed that three endemic species are at the greatest risk:

• Coccyzus ferrugineus, known as cuclillo
• Pinaroloxias inornata, known as pinzon
• Essotricus ridgway, known as mosquerito

In addition to the three above-mentioned birds, there’s also the non-endemic Gygis alba (Holy Spirit or charran blanco) being threatened by the encroaching rats. The charran is a pretty white bird that makes Cocos Island its nesting home.

The intrusive predators from the order Rodentia have been identified as Rattus rattus and Rattus norvegicus. Ms. As part of the study, Ms. Orias set up conventional mouse traps across five trails on Cocos Island. The bait used, bits of coconut with vanilla extract, was absolutely irresistible to the rats. A subsequent stomach content analysis revealed feathers of the birds listed above, both juveniles and adults.

Although formal research on just how many rats are scurrying about Cocos Island has not yet been carried out, there are concerns that their feces could be contaminating the fresh water sources of this National Park of Costa Rica. There are visual reports of rats having completely taken over the tiny isle of Manuelita, which they reached by swimming from the main island and across a channel.

The fate of the endemic rodents of Cocos Island is also uncertain; the genetic makeup of the rats coming from the Americas tends to be stronger, and thus the survival of the native gnawers could be compromised as well. For these reasons, boat traffic to Cocos Island is restricted and subject to thorough inspections to check for stowaway rats.