This is kind of old news but needs to be revisited as it’s totally bonkers. Back in 2008 several creditable news sources – such as the telegraph – reported that Iran had arrested two pigeons suspected of spying on their underground uranium enrichment plant.
An Iranian newspaper is quoted saying that one of the pigeons was caught wearing “a blue-coated metal ring, with invisible string”. I’m not entirely sure what the invisible string is about, probably something that spies use though.
After a quick Google search I came across an equally crazy story about Indian police holding a Pakistani pigeon on suspicion of spying, Read more over at GTAP.