As a lifelong birder, and thus someone who is constantly and obsessively monitoring the birds around me, I’ve had my share of rare avian visitors to my various yards. Last week brought the latest such bird, and though it’s a species that breeds right here in Massachusetts, it was by far the rarest “yard bird” I’ve ever had. When you factor in both habitat and time of year, the Bobolink that was hopping around in my front yard last Tuesday was probably one of the rarest birds currently being seen