Moonwatching is like birdwatching with a pair of blinkers.
Just how restricted is the view?
Earth and moon are about 397,000km apart and the diameter of the moon is 3500 km. What this effectively means is that at a point that is 240 metres away, your window of opportunity is merely 2m x 2m. In the best case scenario (good visibility and big birds) at a distance of 3000m, the window of opportunity widens to 26m x 26m. Given that most birds are unlikely to fly at that maximum altitude, when the moon is vertically above, that window of opportunity reduces itself to 17m x 17m.
The following is a chart of sightings for the night of 14th September 2013 (you will see this day being quoted across a couple of other posts) at one of the stations. We had 72 sightings recorded in just 1.5 hours.
Calculating the effective area being scanned is difficult as the different sightings would have come across at different planes. Assuming an average window of 17m x 17m and assuming even distribution (we do not have the readings from the other site on this day, but we have seen good correlation in general) that leads to the next question : if we have recorded 72 sightings in an area of just 17m x 17m what was the flow of migration across a whole kilometer? Or what was the flow of migration across the whole West to East axis of 27km of Malta?
And if all logic holds, that equates to an interesting migration front that would have otherwise been simply missed.