==> Start

At 2 + 3 september 2004 European Swifts (Apus apus) popped up in never before seen large numbers (at this time of the year in our region). That was about 45 days after our population left the region. They were feeding on huge amounts of a swarming diptera species, could not find out which one it was...Were these birds on migration(??). Be aware of all those crammed full crops(?) you can see on several pics. Would you expect that at migrating swifts? All pics taken by me at 2. Sept. 2004 between 6-7 pm 

Sorry for the unfocused images, but I neither have the equipment nor the experience to take razor blade sharp shots of Swifts ;-)

Below: Detail from the photo above

Below: Look at the crammed full crop, can this be a bird on migration?!

Today, 3 september 2004 I tried to make a photo of these large and numerous insect swarms wich might be one of the reasons for the mass-like appearance of these swifts. The diptera started to aggregate from 10 meters and there were dozends of them in sight - the amount of flying biomass must have been bombastic. I have no idea to wich species they belong but for shure they are diptera. 

The photos are all made from the 5th floor.

Below: A detail from a insect swarm - the flies have about 8 mm wingspan

More pics from 2. September 2004: