The questions that have always intrigued me about the clip:
Who made the hole and how long did it take (assumption is "woodpeckers
made it" but I have no idea how long it took to make the hole).)
Most likely the woodpeckers, maybe helped by natural deterioration of
the radome material or a defect in manufacture or installation or both.
HOW did they make it--seems like it would have been like making a hole
in a bass drum with a finger (lot of bounce, not much cut)?
They pecked it. They can go pretty deeply into trees, and at the edge of
the cover there wouldn't be much bounce.
How long did it take to put that many in, and how many worked on the
project?
Unknown, but probably a long time, that's a lot of acorns!
Why didn't some alarm or path measurement disclose the deterioration
before the cavity was packed so full?
I'm sure it did, over a period of months or years the signal strength
would gradually go down as the dish filled up. No immediately obvious
cause, this would be a real puzzler. There's typically a pretty good
fade margin built in to such links, so it would be a very slowly
decreasing RSSI coupled with likely a hockey-stick graph increase in BER
as the dish got fuller. Depending on the RF frequency, could get worse
with rain as the fade margin decreased. It may have been discovered
accidentally if a tech happened to observe a bird while troubleshooting.
Filling half the dish would be only a 3dB decrease, but once the acorns
started to cover the feedhorn it probably got worse in a relative hurry.
I have no idea of the dielectric properties of an acorn, it would
probably vary depending on the moisture content and the RF wavelength
relative to the size of the acorn. 
Were the acorns cooked?
Probably not. RF output likely a watt or two, spread out over a large
area and several tens of thousands of acorns.