How do wild birds communicate? They don't use snail mail, or email or anything written. Most birds communicate vocally, although some are much more vocal than others. One of the most common forms of bird communication is a call note. In small birds, call notes may sound like chirps. In larger birds, call notes may sound like squawks. They use chirps to convey warnings, attract mates, defend territories, and coordinate group behaviors. Some birds also produce birdsong, vocalizations that are relatively long and melodic and tend to be similar among the members of a species. They are often heard during the spring when they are seeking mates.
This cache has nothing to do with birds other than it is hidden where they might live. It is a letterbox that has a stamp related to birds. The stamp is self-inking so bring your logbook along if you collect letterbox stamps. There are a few trinkets for trading, but please do not take the stamp. That's what makes it a letterbox.