More resources on Swifts:
http://www.birdguides.com/species/species.asp?sp=079085
With videos and much more.
http://www.commonswift.org/Webcam.html
Don't miss the Webcam section.
http://www.xeno-canto.org/europe/XCspeciesprofiles.php?species_nr2=1104.80
Singing Swifts.
http://www.seo.org/media/docs/vencejos2.pdf
Full report in Spanish (PDF).
http://www.grefa.org/index.php?module=ContentExpress&func=display&ceid=45&meid=10
GREFA.