Strange wing angle in flight

[Rotarran]

Today at Oshawa 2nd Marsh I saw a relatively small bird (approximately Killdeer size) fly away from me and from behind I saw its wings bent basically down like an upside down V or I guess an A shape.  It would flap its wings very rapidly but never spreading the wings out completely ...always in that upside down V shape even while flapping...then it would coast a bit (same shape) and then a few more fast flaps and then coast a bit.  Due to the silhouette effect, I did not notice any other features.

It was the oddest flight I have ever seen and didn't think any bird could even keep itself in the air flying like that, but there it was.

Any idea what that could have been?  Maybe some sort of rail or shorebird species?

[Tobias Timm]

Could it have been a kestral hovering?

https://www.youtube.com/watch?v=s0RNjrYIs0E

[Rotarran]

No I'm quite used to seeing Kestrels and I would have recognized their hovering.  This bird's wings was 90 degrees max during flight and coasting.  

My best guess at this point would be a Tree Swallow...although a bit smaller than what I thought I saw, it is probably capable of pulling off this type of flight, seeing how talented aerial acrobats they are.  Still weird why it would choose to fly like that...maybe just for fun, to show off.  Also there were plenty of Swallows there today.