I though possibly some kind of Euc, but I've never seen long, thin, almost "tassel" like flower clusters on a Euc. There are actually many species of Acacia with "sickle" type leaves, there is even a special name for this shape of leave, starts with "p" but I can't find it again. But then again, the bark I see in the background looks Euc-like to me. If the OP found any seed pods, that would be a good clue, acacias have long, thin, flat pods typical of legumes, Eucs have a small, hard, woody capsule. Really, I'm a public menace when it comes to trying to ID a tree half the world away in a climate nothing like mine -- well, at least my heart is in the right place, trying to be helpful. :-)

I was going to say erromena or royal standard, but I see the purple in the flowers so I am leaning erromena. Not ventricosa, that one has the bell shaped (not trumpet shaped) flowers. Alexa

stay with it and try to catch them when the light is strong enough to see by and you might just be rewarded by what can only be described as a bird vortex...when they finally go to roost they will swirl tighter and tighter around the chimney or other suitable spot and one by one drop out of this formation to make their final approach. Unfortunately, if you are in a more heavily urban area with too much light pollution, the street lights coming on right at dusk might make seeing activity above them tough, but keep trying. Its a marvelous thing to watch. The nightjars are much much larger and have a loud distinctive "BEER!" call, and can be heard cruising above parking lots long into the night. for a recording of chimney swift twittering and other id tips, copy paste this: http://www.mbr-pwrc.usgs.gov/id/framlst/i4230id.html

FWIW, silk can be rough or smooth, so you can't always tell from simply looking @ it. Easiest way to tell is a burn test of a few fibers. Take 1 or 2 short threads from an inconspicuous spot & hold them w/ tweezers or pliers up to an open flame(lighter, candle, match) until they start to burn, then quickly put it out & sniff the smoke. Linen & cotton will smell like burning paper & make a soft ash, silk will smell like burning hair or feathers & makes a sort of crispy ash.