Are the spikes so poorly attached that they fall off their mounts and the birds take them as they fall, or do the birds use special spike removal tools?
I looked up pictures of this, and it seems that one kind the birds are using is very thin long nail-shaped spikes pushed through a strip of sticky paper shaped like a series of diamonds. The nests were formed with the sticky paper diamonds and spikes, so it seems like the birds figured out how to lift the entire thing up off the glue-y surface.
Truly amazing!