Hello Tim---thanks for responding to musings.   Sadly, nobody in Ohio did.  I have a Zoology degree and ~ 25 years birding experience, so I like to think alot about numerous questions related to birds and nature in general.   Oh yes, I agree with you that gulls instinctively recognize jaegers as threats.  But why do all the gulls behave as one?  Of the 3 jaeger species, only pomarines would actually attack gulls the size of RBGU.  According to published literature, a RBGU should not even worry about a dainty little LTJA, and parasitics "go for the food, not the bird itself".  Only poms are a serious threat as a predator.  I would think gulls could ID the jaeger species much better than humans can.  But in a surprise attack, better safe than sorry in that first instant.  Actually, my first thought when the dark POJA came winging over the breakwall at Conneaut this Nov. was "peregrine?!".  Perhaps that's what the gulls thought, too.  Now there's a serious predator to fear.
 I'm sure you have seen gulls react to bald eagles.  I suppose other raptors like snowy owl, gyrfalcon,etc. would scare gulls also.  And skuas, which of course are closer to jaegers on the family tree.  But I still wonder why a gull as large as herring or great black-backed would waste precious energy and risk injury by collision when it could just stand there and ignore  a passing PAJA.  Obviously, there is adaptive value to the behavor.  And I still wonder how many jaegers pass through the Great Lakes each year.  Again, thanks for responding.  I wish more of our local birders would do more thinking and less listing.    Later, Craig      P.S. I'm still not great at navigating the web, so I add this thought here instead of at the beginning of the message.  I hope it's not improper to send this out to Ohio-birds; it seems to be a topic of interest to birders anywhere in the Midwest.  And I don't mean to tick off anyone, just want to stimulate some brains out there.

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