Hi, Lisa. Sorry to hear about the missing egg. Where are you? What type of snakes do you have? It is unusual for most species of snakes to raid a nest and take only one of five eggs. It is not unusual for a female BB to pass a defective egg out of the nest, however. Without any additional evidence of snake intrusion, at this time, I would guess that things are okay, for now. Also, if your BB pair have bonded to the nest box to the extent they have thus far (nest, five eggs laid, dive-bombing you when you monitor the box, etc.) I don’t think there is much risk of them abandoning the box if you monitor it more frequently. Keep a close eye on things as best you can, until you are able to solve the missing egg mystery, at least. Best of luck, and let us know what else you find out.
Randy
Bedford, New Hampshire