Malcolm Stewart wrote:
I'd like to try recording birdsong using a microphone at the focus of
parabolic reflector.
Currently, I'm having difficulty thinking of domestic items which I could
cannibalise for their parabolic shape. Any ideas would be welcome. Best
I've thought of so far is an old radiant heater with the cylindrical heating
element at the centre of a spun reflector.

Old (solid) satellite dish.

For 7Khz song, you need surface accuracy of 1/4 * 340m/s /7000Hz = 1.25cm.
One way of cheating is to take a strip of plywood.
Now, form it into a curve.
Yes, it's flat, but as long as it's only a small strip, it can fairly well
approximate a strip of a parabola.