Departure: A short and incomplete history

There has been much speculation out and about in the comments at Sb and elsewhere that a [sigificant, distressing, salient…you name it] number of blogs have departed Scienceblogs this year. Some of the bloggers in question have left signoff messages or commented elsewhere to the effect that they are leaving in a huff, which fuels this speculation.
Being a relative n00b around these parts I was curious about the ebb and flow of blogs on ScienceBlogs over the years since launch. Have we witnessed an unusual flurry of departures in the past couple of months? Let’s review the data*, shall we?