I'm slowly but surely trying to answer my own owl questions. It appears that Short eared owls are more active at dusk, rather than dawn which makes logical sense. At dawn they have been sitting all day thinking about a juicy vole so when the sun sets they are up and about. At dusk they are thinking about a fluffy grass patch and they're ready to call it a night.
Here is an interesting article on Long eared owls (LEOs) and their dependence on voles. This helps to explain the movement of LEOs and the massive disparity in sightings from year to year. Based on this article I would assume that prey availability has either kept the owls that were roosting in Bucks county last year in another spot or maybe the prey availability is down in the Bucks park. I'm hoping to go back one more time in winter to both Bucks and Mercer county to see there are anymore owls around. I would imagine that there is quite a bit of movement even during the winter months based on prey availability.
LEOs are becoming more and more fascinating to me based on their communal roosting as well as the fac that they hunt predominantly using sound. Research indicates that LEOs have the best hearing of all owls and they can hunt in 100% total darkness - WOW! I guess sneaking up on them during my owl prowls is a joke..... I probably sound like a herd of elephants to these guys.
BTW, did you see the LEO pic on the link - WOW. I'd love to get a pic like this, although I suspect that this particularly LEO was flushed from its roosting spot.