The postcard is from Eric during his travels in Brazil. The postcard is dated 12 April and the stamp on it reads 13.4.12. According to Wikipedia, the dating system in Brazil follows the format, day/month/year. Therefore, Eric wrote this letter on April 13, 2012. Currently, he is in Lencois, and he writes to his “fellow birders” about his search for the Black-Capped Nightingdale. but It hasn’t been seen for decades, but the older generation in Lecois believe it flew to NE. WhoIsStraka, Eric is actually looking for FXC, but he must not reveal his mission so he writes in code. In addition, Eric tells them to destroy the cards that follow.

“Rivalries are fierce in birding circles.”
Eric’s reason for readers to destroy the postcards may be code. Most likely, he means that there are other people searching for FXC and thus, he must remain as secretive as possible in order to find her first. If FXC finds out that Eric is looking for her, she may go to any lengths to preserve her secrecy which may be pose a danger to Eric’s safety.