The song of the Swallow

Whilst in Greece recently, we had families of swallows nesting over the balconies, encouraged by the lovely family who ran the hotel, who put up platforms under each nest.  We were entranced by the song the parent swallows 'sang' to their babies still in the nest.  They flew in, sat on top of the aid-conditioning units, or the platforms of an adjacent nest.  The song was a delight, musical, different 'phrases' - like a caged canary, with a trill and a trrrrrrrrrrrrrrrrizzzzzz at the end. Each pair of swallows had a slightly different note, so you could tell whether it was 'Room 1' swallows, or 'Room 3', who were singing.

It's not something I've ever heard before, only hearing the swallows overhead when they just 'tweet'.  Has anyone else heard this song?