It will be interesting to document this phenomenon as the summer goes on. As a guide to focus search efforts in the best habitat, the habitat notes from Mulvihill (1988) are very helpful. Of the 32 sites, 16 were large strip mines with a mix of grass and legumes (clover, Trifolium sp. etc), and 11 were unmown hay fields with a similar composition, although maybe more grasses. 2 fields were listed as weedy or fallow, 2 were pastures and 1 was a clover field.
A feature that all the fields shared was that they all had perches that the Dickcissels were singing from. This included everything from scattered saplings, shrubs and tree rows, to utility poles and barbwire.
Shawn Collins was kind enough to provide some photos of the habitat where he found Dickcissels in Clarion County. Click on them to enlarge and make yourself familiar with the habitat so you can check these areas out when you come across them.
It would be fantastic if any Dickcissel sightings are submitted to eBird. As you can see in the screenshot below, many of the Dickcissels already found have been entered into eBird. These are all sightings from 2012, red pins are within the last 30 days.
For some photos taken by Alex of a group of Dickcissels in Mercer County, click here.
Mulvihill, Robert S. The Occurrence of Dickcissels (Spiza americana) in Western Pennsylvania during the 1988 Nesting Season–Its Possible Bearing on the Species’ Unusual History in Eastern North America. Pennsylvania Birds. V2 No. 3. http://www.pabirds.org/PABIRDS/BackIssues/PBV02N3.pdf