The northern fowl mite, Ornithonyssus sylviarum. Specimens courtesy of Dr. Bobbi Pritt of the Mayo Clinic, Rochester, MN.
Specimens were collected from a bird's nest that was brought in by a concerned person. Host bird uknown. As with many clinical arthopod specimens, precise location and date of collection isn't always available. I will update as I get any additional information.

Also, contrary to BugGuide's policy, these images are not all from the same individual. I had to study several individuals to get detailed shots of diagnostic features.

Diagnostic features are:
-chelicerae shear-like (Image 2)
-dorsal plate broad, not completely covering dorsal surface (Images 3 and 4)
-spiracle present between legs III and IV; notice the trachea extending anteriorly (Image 5)
-genitoventral plate narrowed posteriorly behind the legs (Image 6)
-sternal plate rectangular, with two pairs of setae on the plate and the basal setae (bottom) just off the plate (Image 7).