Sorry for the delay in posting this - I had to rush off to work from our early morning birding.
Zeke Cornell and I had the MacGillivray's Warbler this morning at about 7:00 am in the same place where Steve Mirick reported it yesterday:
along the bike trail just north of the fresh water pond, in an area of dead sumac and goldenrod. It was chipping loudly and we saw it only briefly before it moved back out of sight. The view I got was excellent, if brief, and I could see the bright, white eye arcs above and below the eye as well as the yellow breast, gray hood and green back. We could not entice it out again.
We did not find the Yellow-breasted Chat but we did have some nice warbler activity on the Boy Scout Trail.
The Clay-colored Sparrow was seen by others this morning in the vicinity of the bunker by the Seacoast Science Center. The flock of Chipping Sparrows appears to move around the bunker so check all sides, including near Edalhab and the parking lot behind the Science Center.