I visited the nest this morning before dawn, I arrived about 6:30am and neither adult was on the nest. My intention was to apply a technique for locating Coopers nests by listening for pre-dawn vocalizations by the adults (don't really need to locate the nest per se since it's already been found, but I wanted to apply it anyway). Right on cue at exactly 6:45 I started hearing vocalizations from the male - it took me a bit of walking through the woods to figure out where he was, but he was perched in a tree somewhat east (taking Glen Erin to be essentially north-south) of the nest tree. Shortly thereafter the female started replying - she was in a large tree further south and close to the path that goes towards the old nest, right around where the Maplewood Park sign is.
The kept vocalizing to each other on and off (the male was making the short 'chip' or 'kik' call which is a common "I'm here" call for the male, and the female was making the standard kek-kek-kek call in reply), and would occasionally both fly to different spots. At one point the female flew to the woods immediately south east of the old nest, and the male was perched immediately across from it. Eventually the male made his way up to the nest and perched in there for a with the female a few trees away.
I have never applied this technique before, but the pattern of pre-dawn vocalizations with the adults should cease once eggs are laid - they go entirely quiet once incubation starts. So this, combined with the fact that they definitely weren't on the nest overnight while it was snowing and raining, certainly suggests to me that no eggs have been laid yet. If someone wants to get out there over the next days at the same time, hearing them go quiet might be the surest indication that an egg has indeed been laid (the nest is about a 15 min drive from me so I make no guarantees about being able to get up early enough to get out there on a regular basis
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