There has been a lot of talk on the PABirds listserv regarding a possible decline of Blue-headed Vireos based on the scarcity of individual sightings this fall. I decided to look into some eBird graphs to see if our collective eBirding can shed some light on the discussion. The graphs do have to be taken with a grain of salt because they are showing what is basically raw data, but I believe that they can give us a broad idea of what is going on.
The graphs below are for Pennsylvania with a line for each of the years 2007-2011. eBird currently only allows for 5 years to be shown on the graph at once. From these graphs it is clear that we are not having a great year for Blue-headed Vireos, but it is also not a bad year. On most of the charts, the dark blue-gray line for 2011 seems to be right in the middle of the five years, except for the week of 10/8. I think I remember that as a particularly rainy, miserable week.
So the conclusion from these charts is that, at this point, there is probably nothing to worry about. Maybe locally low numbers were offset by high numbers of Blue-headed Vireos elsewhere in the state. However, with individuals indicating that they saw noticeably less Blue-headed Vireos this year, it is worth keeping a close watch come next spring and summer.