[mou] need id help

[linda]

Thanks to Bruce Baers' post I headed to Old Cedar/Bass Ponds this 
afternoon. Some of the water fowl on the large open pond took off as I 
approached from the west on the middle dike, but I did see the coot, the 
ring-neck, and the redhead (great looks on those) among the mallards.

However, as I was perusing the flotilla of mallards, about half-way down 
the dike, along from the east came a striking raptor, not quite like any 
I've seen.

Flying parallel to the dike at just above head height, it appeared to 
study the waterfowl. It skimmed past with a few strong beats, then 
crossed the pond toward the river at about where the recently 
constructed outlet is. It continued cruising along the shoreline a bit, 
before dropping toward the water, out of sight. When I rounded the east 
end of the pond, it suddenly reappeared behind me, as though it had 
circled back around, and glided low over my head, then above the trees, 
toward the river again. I got a good look at its undersides in my 
binoculars.

It was almost pure white underneath, but the tips were "dipped in 
black," and there was a thin charcoal gray border on both leading and 
trailing edge. There was only the faintest hint of pale gray streaks on 
the chest. Its upper plumage appeared to be a solid pale to medium gray, 
with a notable lighter spot on the rump, but this uniformity of color 
may stem from the nearly horizontal angle of view. The tail was 
rectangular. The wings resembled those of a falcon in silhouette, but 
this was bigger than a peregrine.

I'd appreciate some help with id.
Linda Whyte