Fork-tailed Swifts appear over Robertson

These birds suddenly appeared over my house, two mornings ago. I knew straight away that they were Swifts, but I was not quite sure which Swift? The bird formerly called the "Spine-tailed Swift" (now officially the "White-throated Needletail") is the more usual species, south from Sydney. I have not seen many Swifts here, since moving to Robertson. I often look out for them before a summer thunderstorm, but have only seen them on a few occasions, over 6 years.

I should mention that all these images were taken from my back deck (so they qualify as birds from my backyard).

Click to enlarge the image. There are four swifts in the frame.

But, as I said, which Swift was I looking at?

The thing about Swifts is they fly so very, very fast (they get their name for a good reason). These birds were hawking at about twice the height of the local trees, and then circling higher, and swooping back down to just above the tree tops. Their speed and their circling was a real challenge, to try and track them. No autofocus job, this. I tried to monitor a bird as it flew away from me, then watched it come back, adjusting the focus , in an attempt to get a shot, as the bird raced back towards me.

Swift, at about 300 metres range.
(Shoalhaven Valley in distance)
The photographer's challenge is to focus on the distant bird,
then adjust focus as the bird comes zooming back
(they were circling constantly, for about 20 minutes).
Adjusting focus on a high speed bird is a great hit or miss experience.

My best shot.

For photographers, the speed settings was 1/1000th of a second.
Aperture F/5.6, with maximum zoom (300mm focal length).

This shows the elegant flight pattern of this species. Beautiful wings. The design is, of course, the sort of design aeronautical engineers can only dream about. The white rump is diagnostic (to distinguish it from the White-throated Needletail, which has a white throat and white undertail coverts, but the rump is brown).
I wish to acknowledge the assistance of Geoffrey Dabb (of COG) in confirming my ID of these birds as the Fork-tailed Swift (Apus pacificus) (a species I had not seen before).
I like this image - it shows the colour of the upper parts of the bird, and wings, plus the white rump. The wing shape, as it curves around, while diving, is very elegant.
A blurry image, but it does show the long tail, clearly forked.

High speed shot of a passing, zooming Fork-tailed Swift.This one is gliding away from me, at high speed.
This blurred image shows the Fork-tailed Swift with tail in full spread (a deep "V").
Almost certainly this bird is using its wings and tail for full control as it strikes at an insect.

A composite image (5 frames) of Fork-tailed Swifts,
showing the changes in wing shape and profile, as the birds tumble, zoom and soar.
Click to enlarge

Fork-tailed Swift with another species of bird. But which other bird?

This next image had me thinking Tree Martin,*** but on reflection, the bird in the image (relative to the Swift) is larger than a Tree Martin would be, and, as there was a hot north-westerly blowing, on which all these birds had travelled in, it is entirely possible that it is a White-breasted Woodwallow. Woodswallows are known to move about on favourable winds, following swarms of insects. Even the shape of the wings is "right" for a Woodswallow, (and wrong for aTree Martin), now that I think more about it. *** I have since decided that this is sufficiently unlikely to be a White-breasted Woodswallow, that I cannot "claim" that species. It is more likely to be a Tree Martin. The photo is not good enough for a positive ID, one way or the other.